Radiator Choices - Cooling System Info

David I'm throwing this in mostly for the new guys reading your thread, but I've made comments regarding radiators that apply to your question. It helps to review why we do the things we do.

Cooling system description

The Pantera's cooling system consists of a short list of components:

• A high flow thermostat and controlled bypass system integral to the 351C engine block.
• A centrifugal coolant pump integral to the 351C engine block and driven by the crankshaft. The crankshaft and water pump pulleys are unique to the Pantera, they are smaller than those employed in other 351C equipped Ford and Mercury vehicles. The pulleys are both 5.5" in diameter; the pulley ratio is therefore 1:1 meaning the coolant pump operates at the same speed as the engine (note: the coolant pumps in Ford and Mercury vehicles without a/c were 4% under-driven and they were 10% over-driven when the vehicles were equipped with a/c).
• A twin pass cross-flow radiator mounted in the front of the car
• Dual electric cooling fans mounted in front of the radiator; one cooling fan was thermostatically controlled and the other manually controlled in the earliest Panteras, and both fans became thermostatically controlled in 1972. The fan controls consist of a pair of relays controlled by a pair of thermostatic switches mounted in the right hand radiator tank.
• Two tanks located in the engine compartment. The first tank, referred to as the system tank (also referred to as a pressure tank or a supply tank) is configured as a functional de-gas tank except it has the cooling system’s pressure cap mounted on top instead of a vent. The second tank is plumbed to function as an expansion tank (a pressurized recovery tank).
• The cooling system plumbing consists of 1-3/8" OD metal tubing which runs below the car to connect the radiator to the rest of the cooling system located in the engine bay behind the passenger compartment.

The 351C controlled bypass high flow cooling system

The 351C was designed to employ a Robertshaw high-flow thermostat as standard equipment and it incorporates a unique high-flow warm-up system Ford called a controlled by-pass system. A high volume of coolant was recirculated within the block (bypassing the radiator) during warm-up. This high flow bypass system prevented the formation of hot spots in the cylinder heads while warming the motor to operating temperature more quickly and more evenly.

Diverting a high volume of coolant away from the radiator would lead to over-heating during normal vehicle operation, so coolant recirculation was controlled (shut-off) once the motor reached operating temperature. This was accomplished via a unique 11/16” OD copper “button” on the bottom of the Robertshaw thermostat which extended downward as the thermostat opened and plugged an orifice in a brass plate mounted inside the block immediately below the thermostat. The addition of the 11/16” OD button to the Robertshaw thermostat makes that particular thermostat unique to the Cleveland engine series. The high flow warm-up and controlled bypass aspects of the cooling system built into the 351C were advanced designs for their day, and cannot be improved upon even today but this unique design makes it imperative to locate and use the proper thermostat. The cooling systems of modern motors have similar functionality, but it is accomplished with a "divorced" thermostat, one that is mounted externally from the engine block. The 351C was unique in accomplishing this functionality internally ... and it was accomplished with only a small modification of the standard Robertshaw thermostat. Unfortunately that small modification has been a major stumbling block.



The Pantera's cooling system woes

The cooling system built into the 351C performs admirably if the proper thermostat is installed. Unfortunately the same cannot be said for the remainder of the Pantera's cooling system. Here's a list of the cooling system's many issues:

• A Veglia coolant temperature gage was used in conjunction with an incompatible Ford temperature sending unit. The gage had a maximum scale reading of 230°F even though the cooling system wouldn't boil over until 250°F. Temperature readings often hovered at full scale causing owners concern! In regards to the high temperature readings Ford's technical service bulletin #8 had the audacity to state that readings of 230°F were not abnormal! The 230°F gage was replaced with a gage having a maximum scale reading of 260°F in July 1973. Ford also recommended operating either gage with a 10 ohm - 1/2 watt resistor in series with the sending unit in order to provide a mid-scale reading under normal operating conditions, even though mid-scale was 160°F on the original gage and 190°F on the replacement gage.
  
  
• The ignition controls were augmented by DeTomaso with an electric ported vacuum switch (aka the PVS valve) to contend with the overheating issues Pantera owners were experiencing. The vacuum switch was designed to retard the ignition thereby reducing the engine’s idle speed by 100 to 400 rpm when a predetermined high temperature limit was reached. Retarding the ignition increases the cooling system's heat load, while reducing idle speed also reduces the speed of the coolant pump. This response to high coolant temperature was opposite to the way in which Ford’s ignition controls were normally designed to react to high coolant temperature. The electric ported vacuum switch did not alleviate the Pantera's propensity to operate hot during stop and go driving.
  
  
• The radiator was located in the front of the Pantera, remotely from the engine which was located behind the passenger compartment. The plumbing between the engine and radiator ran below the vehicle, therefore any air in the cooling system was trapped in the top of the radiator without any means of venting. The effective surface area of the radiator decreased as air collected in the radiator; in fact enough air could collect in the radiator to restrict the circulation of coolant in the cooling system. Ford was aware there was a problem with air collecting in the radiator, they made a few different revisions to the radiator vent system, connecting the top of one tank or the other to various locations in the cooling system, including connection to an air removal "venturi" located downstream of the radiator's outlet, but none of the revisions were successful; therefore the Pantera's cooling system has never had a functional air venting system.
  
  
• For any given engine speed the pumping rate of the coolant pump is lower in the Pantera than it was in a 351C equipped Ford or Mercury; not because of the pulley ratio but because the Pantera's cooling system plumbing between the engine and the radiator was more restrictive. The Pantera's plumbing is smaller in diameter (especially between the radiator outlet and coolant pump inlet), it is greater in length, and it has a greater number of bends (especially 90° bends).
  
  
• The coolant pump inlet was originally connected to the under-car tubing via a 90° metal tubing elbow and a 90° rubber hose elbow. This arrangement interfered with the shift linkage in some cases, and the rubber elbow was known to collapse at low engine speeds which severely restricted coolant flow. This plumbing arrangement was replaced in May 1972 by a "double-bend" metal tube which only used a short-straight rubber hose to connect to the pump inlet. The new arrangement created more clearance for the shift linkage and made it impossible for the rubber hose to collapse.
  
  
• The twin pass radiator was originally designed with a vertical baffle in the right hand tank which divided the radiator into a rear pass and a front pass; it was determined the vertical baffle was responsible for some of the Pantera’s overheating problems because too much coolant flowed around the baffle thereby bypassing the radiator. The design of the Pantera’s radiator was revised beginning April 1973; the new design effectively eliminated excessive coolant flow around the baffle by replacing the vertical baffle with a horizontal baffle which divided the radiator into a lower pass and an upper pass.
  
  
  
  
• The electric power for the cooling fans was supplied to the fans through the ignition switch even though there were relays in the fan circuit; in other words a high current load was routed through the ignition switch contacts unnecessarily. This problem is exacerbated when high output fans are installed having motors which draw more current than the OEM fan motors.
  
  
• Power for the fan circuit and the engine's ignition circuit was supplied to both circuits "downstream" of the ignition switch, configured in such a way that the two circuits remained electrically connected even when the ignition switch was in the "off" position. This allowed the "back emf" generated by the spinning fan motors to supply voltage to the ignition system and keep the motor running even though the ignition switch was turned "off". This problem is exacerbated when high output fans are installed having motors which are larger than the OEM fan motors.
  
  
• The oem fan switches operated in conjunction with a 192°F (89°C) thermostat. Both fan switches were installed on the right hand side of the radiator, one above the outlet nipple and one below the inlet nipple. Both fan switches were originally installed in the same tank (the outlet tank) because the radiator was originally equipped with a vertical baffle. One fan switch was set at 158°F (70°C); the other fan switch was set at 185°F (85°C); these settings seemed appropriate based on the original design of the radiator. The switches became located in different tanks however as a result of replacing the radiator's vertical baffle with a horizontal baffle (April 1973). The upper switch remained in the outlet tank but the lower switch sensed the temperature of the coolant in the inlet tank as a result of the revision. Strangely, Ford did not revise either of the fan switch settings in conjunction with the radiator baffle revision, and the fans ran constantly instead of cycling on and off as they normally do in other cars.

The Pantera is notorious for overheating during stop and go driving. The engine running-on after the key is turned "off" was a secondary problem that annoyed owners. The overheating problem was resolved to a degree by two of the changes mentioned above: (1) revision of the coolant pump inlet plumbing and (2) replacement of the vertical radiator tank baffle with the horizontal baffle. The 1974 L model Panteras could idle all day long without overheating, with the the air conditioning operating, on a summer day ... even with the oem 4 blade radiator fans! Most owners would agree however even the 1974 Pantera's cooling system performance during stop and go driving is perhaps best described as "fragile".

To summarize what ARE the primary causes of overheating:

• Air trapped in the radiator, no functional air removal system.
• Coolant leakage around the OEM radiator’s (pre-April 1973) vertical baffle.
• Insufficient coolant flow rate resulting from length, diameter, and number of bends in the coolant system plumbing
• Lengths of rubber hose in the plumbing between the radiator outlet and coolant pump inlet collapse at idle and low rpm, severely restricting coolant flow.

Subsequent contributors to overheating:

• The electric ported vacuum switch
• Insufficient ignition advance at idle (retarding the ignition made the motor less efficient, therefore the wasted heat raised the exhaust temperature and increased the cooling system’s load)
• Insufficient engine speed at idle (slowing the engine reduces the coolant flow rate!)
• The carburetor was calibrated lean for emissions

Contemporary causes of overheating

• Use of the wrong thermostat (number 1)
• The accumulation of air in the radiator or engine block
• The coolant flow rate remains too low!
• Lengths of rubber hose in the plumbing between the radiator outlet and coolant pump inlet collapse at idle and low rpm, severely restricting coolant flow.
• The radiator with a vertical baffle was never replaced
• The electric ported vacuum switch is still in service
• Installation of the wrong pressure cap (insufficient cooling system pressure)
• A poorly operating thermostat
• The engine is in a poor state of tune (ignition or carburetor)
• One or both head gaskets have been installed with improper orientation
• The brass orifice below the thermostat is missing
• The coolant recirculation passage in a Wieand or Milodon coolant pump has not been drilled open
• The radiator is fouled internally by scale
• The under car coolant pipes are plugged with rust
• The anti-freeze is too old (should be replaced every two years)
• Bad wiring connection to the fans causing one or both to operate at a slower speed
• Reversed wiring polarity causing one or both fans to blow air in the wrong direction

Cooling system specs

• Coolant capacity: 6-3/8 US gallons (24 liters)
• Coolant mixture: 50/50 mix of water and ethylene glycol
• Boiling point: 250°F at 13 psi
• Thermostat rating: 192°F (89°C)
• Pressure cap rating: 13 psi

Cooling system parts circa 1975

Replacement thermostat

• OEM-temp (192°F): Motorcraft RT-139 or Robertshaw 333-192
• Lower-temp (180°F): Motorcraft RT-310 or Robertshaw 333-180

Note: The Robertshaw thermostats have been sold in the past by Stant, Interstate and Prestone using the 333-192 and 333-180 part numbers. The thermostats were also sold by Flow Kooler. The 333-180 thermostat was sold in Australia by Dayco under part number DT66A, and it was sold by Summit Racing under part number BRA-333-180. You should check, but it may not be available from any of those sources any longer. The thermostats have been hoarded by certain businesses specializing in Mustangs, 351C engines, etc. Whenever they become available they are sold out immediately.


Robertshaw 333 series thermostat and the brass plate
that presses into the block below the thermostat

The correct thermostats AND brass plates are available from Marlin Jack.
Marlin is a Pantera owner and a machinist. He manufactured the brass plate
in the picture above. Marlin on eBay
Marlin's email: pantera1974@verizon.net

I do not recommend 160 degree thermostats due to the increase in engine wear. see the chart below.



Replacement pressure cap

The pressure cap "neck" of the OEM system tank is designed for European pressure caps, it is taller than a pressure cap neck designed for US pressure caps. Therefore the spring of a US pressure cap is insufficiently compressed and it will not hold the pressure it is rated for. In some cases it will not even seat tightly against the seat. If you cannot find a pressure cap equivalent to the Motorcraft #RS-40 don't despair. You can have a radiator shop replace the European pressure cap neck with a pressure cap neck designed for US pressure caps; or you can purchase an aftermarket tank equipped with the US pressure cap neck out-of-the-box.

• OEM system tank (metric cap): Motorcraft RS-40
• Aftermarket system tank (US cap): Motorcraft RS-50A (standard)
• Aftermarket system tank (US cap): Motorcraft RL-44 (pressure release lever style)

Note: The modern replacement for a Motorcraft RS-50A radiator cap is Motorcraft part number RS-62 or Stant part number 10229. The modern replacement for a Motorcraft RL-44 radiator cap is Stant part number 10329.

Refurbishing the OEM Cooling System:

If you follow the steps below your Pantera will have a cooling system that is in May 1973 show-room condition, with one helpful change (elimination of the electric ported vacuum switch) and one helpful addition (a drain cock installed in the top of a radiator tank to make it possible to manually vent the radiator). Don't be concerned about disabling the vent line in order to install the drain cock, because the vent system never worked anyway; this is why it is necessary to manually vent the radiator in the first place. If you do nothing else to the cooling system one mechanical problem shall still exist, i.e. the coolant flow rate shall still be too low. The three electrical problems of the radiator fans are also left unresolved: (1) the fan controls supply the fan motors with power routed through the ignition switch, (2) the fan motors can back feed power to the ignition when the key is turned off, and (3) the fans are always "on" instead of cycling "off" and "on".

Make sure your Pantera's cooling system incorporates these factory revisions:

• If the coolant pump inlet connects to the under-car tubing via a combination of a 90° metal tube elbow and a 90° rubber hose elbow replace that arrangement with the upgraded "double-bend" metal tube which only uses a short-straight rubber hose to connect to the pump inlet.
• If the radiator is still equipped with a vertical baffle replace it with a horizontal baffle, or replace the entire radiator

Helpful changes:

• Remove the electric ported vacuum switch if it is still in service, it does more harm than good. The only vacuum control recommended for your ignition is one hose connecting the distributor’s vacuum advance directly to the carburetor’s ported vacuum connection or the intake manifold's vacuum connection.
• Install a drain-cock in the top of one of the radiator's tanks where the fitting for the vent would normally be installed, thus making it possible to periodically vent air from the top of the radiator manually. This also helps purging air from the radiator when filling the system with coolant. Remember to plug the fitting where the other end of the vent hose connects to the cooling system. This drain-cock is not necessary if the tanks are modified to automatically vent air from the cooling system as described further below.
• Any length of hose between the radiator outlet and the coolant pump inlet MUST be internally supported to prevent it from collapsing. The OEMs often accomplish this with a coiled wire. You would have to buy a 1-3/8 diameter suction hose and remove its coiled wire for use in your Pantera. You could also insert a length of 1-3/8 OD stainless tubing inside the hose. OR … you can use hose that is so thick and so stiff that it resists collapsing (Gates).

Refurbish:

• Install a new Robertshaw 333 series thermostat (most Panteras have the wrong thermostat installed)
• Replace the radiator core or replace the entire radiator
• Service the fan motors (new brushes and bearings) or upgrade the fans with fans rated for increased air flow
• Replace the coolant pump if the shaft bearing has play or if the pump is decades old
• Replace the rubber hoses throughout the cooling system (see the warning below)
• Replace the coolant tubes if needed
• Replace the tanks if needed
• Replace the pressure caps

The Hall Pantera Phoenix radiator makes a practical replacement for the oem radiator for 3 reasons: (1) its less finicky about coolant chemistry because its made of copper, (2) it looks and functions like the oem radiator, and (3) it has an "open" core design that offers low restriction to air flow, making it ideal for use with oem style pusher fans.

The Hall Pantera Mirriah fans were practical replacements for the oem fans. They were equipped with 10 blade Flex-a-Lite fan blades, Hall claimed they moved four times more air than the oem fans. Hall also claimed they drew only 7 amps per motor even though they moved more air than the OEM fans, which draw 8.8 amps per motor. That's 14 amps total compared to the OEM fans which draw 17.6 amps total or the Flex-a-lite model 220 fan assembly which was also equipped with 10 blade fans but was rated at 19.5 amps.

Unfortunately the Mirriah fans are no longer available. Similar fans ARE available from Cool Cat Corp however. And Flex-A-Lite fan blades can be drill-out to fit the larger diameter shafts of the Cool Cat fan motors. https://www.coolcatcorp.com/product/CoolCatFan38.html

Warning The plumbing for the heater core is routed through the center console and up under the dash board. That plumbing includes some rubber hoses. If one of those hoses should burst while you are driving your Pantera it will fill the interior with steam and you won't be able to see where you are going. There is one particular little hose adjacent to the accelerator pedal, if that one should burst it will scald your right foot with 180 degree coolant, you won't be able to keep your foot on the accelerator OR use the brake pedal. This happened to me, which is why I am emphasizing do not neglect to replace the heater hoses within the passenger cabin as you refurbish the cooling system.

Parts Choices

RADIATOR:

I'm not going to be too adamant about radiators. Regardless if you choose to recore your OEM radiator or purchase an aftermarket replacement, all Pantera radiators seem to be capable of performing the job they were designed to do. Here's some radiator info I've learned along the way.

The extra cooling capacity of an aftermarket radiator will be most beneficial for high load driving (high speed, uphill) and driving in very hot climates. Unless your Pantera is equipped with an early radiator having a vertical baffle, or unless the radiator core is fouled by scale, or unless you drive your Pantera in a very hot climate the radiator is not the problem when the engine overheats during stop and go driving. That problem is most likely a combination of the wrong thermostat, air in the system, hose collapse between the radiator outlet and pump inlet, and insufficient coolant flow. For instance, an aftermarket radiator full of air is no more effective at cooling than the OEM radiator full of air. This is not to say the extra cooling capacity of an aftermarket radiator combined with the higher air flow of aftermarket fans may not help a cooling system that is marginal during stop and go driving ... it may ... but it does not address the primary source of the problem.

The choice between copper or aluminum for a radiator should not be a point of argument. Race car builders like aluminum mainly because it is lighter, although there are choices in core design available in aluminum that aren't available in copper. Aluminum radiators can withstand a bit more cooling system pressure than copper radiators because the way in which they are assembled is sturdier than the tin-lead solder used to assemble copper radiators. Today's new car manufacturers have turned to aluminum because it is less expensive than copper. Both metals radiate heat well and both are suitable for use in building radiators. Copper radiators are less prone to being damaged by the condition and chemistry of the coolant, but they are heavier than aluminum radiators and usually more expensive.

The extra cooling capacity of an aftermarket radiator having a thicker core than the OEM radiator will make the cooling system more rugged for high heat load applications, such as driving uphill over a mountain pass on a hot summer day. It is also beneficial for racing or continuous high speed driving. The usual choices in aftermarket radiators include the Phoenix radiator sold by Hall Pantera (copper), the Ron Davis radiator sold by Pantera Performance Center (aluminum) or the Fluidyne #FHP35-PAN radiator sold by everyone else (also aluminum). I must emphasize however the extra cooling capacity of these radiators may not improve cooling problems which occur during stop and go driving.



Left Picture: The Hall Pantera Phoenix radiator;
Middle Picture: The Fluidyne radiator (older FHP30-PAN version);
Right Picture: The Ron Davis radiator

According to Evan's Cooling a radiator the size of the Pantera's radiator with about a 3" to 3-1/2" thick core (i.e. the core thickness of the aftermarket radiators) is good for up to 500 BHP under racing conditions; that should be all the cooling capacity a street operated Pantera shall ever need. As a radiator's core becomes thicker the more it impedes the flow of air. Making the radiator core of a Pantera thicker than 3-1/2" "may" actually hurt the cooling system's performance during stop and go driving by reducing air flow. A custom radiator equipped with a thicker core should pose no problem however for a Pantera race car.

Radiators must be mounted loosely in rubber. There must not be any solid attachment to the chassis, they must be independent of the chassis so any twisting or flexing of the chassis is not transferred into the structure of the radiator.

TANKS AND PIPES:


Stainless steel tanks and a stainless steel coolant pipe kit (1-3/8" OD or 35mm tubes).
If your Pantera needs new tanks or pipes, these should be a life time investment.



This is a 35mm x 38mm silicone hose reducing elbow for connecting the 1-3/8"
coolant tubes to the 1-1/2" radiator nipples of the older FHP30-PAN Fluidyne
radiator. The new FHP35-PAN Fluidyne radiator has 1-3/8" nipples.

FANS:

The small 4 blade oem fans move a reasonable amount of air, if you increase the coolant system's coolant flow rate you may find the oem fans are adequate for your application. This is not to say there isn't room for improvement; higher capacity fans will obviously push (or pull) more air through the radiator during stop and go driving and thus improve the performance of the cooling system when its needed most. There are 4 ways to install replacement fans in a Pantera.

• Attached to the original mounts in front of the radiator
• Affixed to the front of the radiator
• Affixed to the back of the radiator without a shroud
• Affixed to the back of the radiator with a shroud

Although fans mounted to the front of the radiator are not as common as fans mounted to the rear, the front mounted fans offer four benefits: (1) oem appearance (2) the radiator can remain up-right (3) no shroud is necessary (4) the fans and the radiator plumbing do not interfere with one another.

Spal is an Italian manufacturer of electric fans that are commonly used and respected throughout the automotive industry (OEM applications, professional racing, motorsports and the aftermarket). Spal fans are available in a wide variety of sizes, configurations and air flow ratings. Flex-a-lite is another reputable manufacturer of electric fans based in the USA.

Always mount the fans in such a way that there is a gap of approximately 1" between the fan blades and the radiator core. Mounting the fans too close to the core will reduce the air moving capacity of the fans. Fans should never be mounted directly to the radiator core. The black plastic ties supplied by fan manufacturers for mounting in that fashion will wear against the tubes in the radiator core and eventually create leaks.


The Hall Pantera Mirriah fans mount in the oem brackets

Mounting one or two high volume fans behind the radiator with a fan shroud will optimize the Pantera's cooling system for street use, the shroud spaces the fans properly away from the radiator core to maximize air flow and it assists the fans in drawing air through the entire surface of the radiator; but a shroud should not be used for a race car or a car driven at sustained high speeds, as it will impede air flow through the radiator at high speeds. The most popular option for mounting fans behind the radiator on a shrowd has been the Flex-a-lite model 220 fan assembly mounted behind the Fluidyne radiator. The Fluidyne radiator has straight nipples (hose connections) instead of angled nipples like the oem radiator making installation of the shrouded fan assembly possible. The two 12 inch fans move air at 2500 cfm (combined) and draw 19.5 amps total. The model 220 fan assembly is no longer available from Flex-a-lite however, it has been replaced by the model 420. As far as I can tell the only difference between the two fan assemblies is the model 420 fans have 8 blades each instead of 10, and current draw has increased to 22 amps total. The air flow rating of the fans is unchanged.

PUMP:

I'm not going to be too adamant about coolant pumps other than to say the pump speed needs to be increased! Here's some coolant pump info I've learned along the way:

A coolant pump that flows more coolant at low engine speed should help alleviate over-heating in stop and go traffic. For the best high-flow at low rpm performance the Flow Kooler pump is the way to go, according to several Pantera owners. Flow Kooler coolant pumps have a unique impeller specifically designed to improve low rpm flow. Their 351C pump is p.n. 1648. Stewart components is another pump manufacturer that is highly recommended. Their stage 1 pump for the 351C, p.n. 16143 is advertised to be "high flow" without any further explanation.

The pump for those seeking the highest flow rate possible is the Stewart Components stage 4 pump. The Stewart Components stage 4 water pump flows 160 GPM! If high flow is what you need, that's the pump. Pantera Parts Connection modifies the Stewart Components 351W pump for Clevelands and sells them ready to bolt on (I believe modification involves removal of the back plate and drilling two holes).

If you're going to use the car in applications where it will be run continuously at high rpm consider the Edelbrock #8844 pump, which is equipped with a cast-curved blade impellar. The forte' of pumps with curved blade impellars is high rpm, they don't cavitate until about 7000 rpm, whereas the pumps with stamped steel impellers are cavitating by 5000 rpm. The pumps with stamped impellers still pump coolant when they cavitate, but they consume about twice as much power. The Edelbrock pump saves about 5 bhp at 6000 rpm. Edelbrock makes no published claims of super high flow rates.

If you're going to use the Weiand #8209 coolant pump, the Milodon #16235 (hi vol) coolant pump, or the Milodon #16335 (std vol) coolant pump I recommend drilling out the recirc passages to at least 5/8"; the passages are plugged as the pumps come out of the box. Drilling out the passages will allow the 351C recirc system to function as designed, it will allow you to use the proper thermostat, and your motor will warm up properly.

The Laws of Physics Governing the Performance and Behavior of Cooling Systems

• The cooling system is a closed loop fluid system. In order for coolant OR air to flow from one place to another within this system it MUST flow to a zone of lower pressure. It is impossible for it to do otherwise.
  
  
• Gases (such as air) are compressible. If the volume of a gas remains constant when it is heated or cooled the gas pressure shall simply increase or decrease.
  
  
• Fluids (such as a 50/50 coolant mixture) are not compressible. As fluids are heated or cooled their volume shall expand and/or contract. A closed loop fluid system must make allowance for the expansion and contraction of the fluid.

Drawing Detailing the Pressure Zones Within the OEM Cooling System



Observations:

• It is contrary to the laws of physics for air to flow from the radiator to the system tank (swirl tank). Observe the picture above; the tanks at the top of the radiator are in lower pressure zones.
  
  
• In order to prevent air from having an impact upon system performance it must be isolated from the system. Air removed from the radiator and inserted back into the system elsewhere (at the system tank, in the downstream plumbing, etc) shall simply circulate through the system and end up back in the radiator again.
  
  
• Fluids are not compressible. With the system bled completely of air as it should be, there is no allowance for the expansion or contraction of the coolant within the closed loop system other than via the pressure relief design of the radiator cap. The coolant MUST flow between the pressurized closed loop system and recovery tank (in and out via the radiator cap) to allow for the expansion and contraction of the coolant.

Modifying the OEM Cooling System (fixing the problems):

The modifications I am about to suggest compliment the factory revisions mentioned in the refurbishing section; make sure your Pantera's cooling system incorporates those factory revisions. These additional modifications are aimed at two things: (1) correcting the mechanical problems I identified as primary problems with the goal of making the Pantera's cooling system rugged and dependable with the least amount of modification to the car, especially visible modification; and (2) correcting the electrical issues of the fan controls.

(1) Increasing the COOLANT FLOW RATE improves the cooling systems performance during stop and go driving. There are four methods I shall share with you.

(1A) A simple bolt-on way to increase coolant flow is to install a smaller diameter coolant pump pulley to “overdrive” the pump by 10% to 25%. A high quality 4.9" pulley which over-drives the pump by 10% is available from SACC Restorations. Over-driving the coolant pump by 10% is not excessive, there is nothing to fear. The coolant pumps of 351C equipped Ford and Mercury vehicles were also over-driven by 10% when the vehicles were equipped with air conditioning. Feedback from owners who have installed the pulley has so far reported 5°F and 7°F reductions in coolant temperature at idle.



(1B) The second method to increase coolant flow is to install a coolant pump designed to pump more coolant. Some Pantera owners speak highly of the pump manufactured by Flow Kooler (p.n. 1648) which is designed to improve coolant flow at low rpm. Another option for consideration is the Stewart Components pump (p.n. 16143).

(1C) The third method to increase coolant flow involves increasing the size of the plumbing from the radiator outlet to the coolant pump inlet. There is no kit you can buy to do this, you'll have to fabricate the parts yourself using 1-3/4" OD metal tubing. The radiator's outlet nipple should also be replaced with a corresponding 1-3/4" OD outlet nipple.

(1D) The fourth and final method for increasing coolant flow is to install an electric booster pump at the radiator outlet. Stewart Components sells two such pumps for this application, model E558A and model E389A. These pumps are compact and lightweight. They are designed in such a way that if they fail they will not block the flow of coolant in the cooling system; this is a very important feature. Both are rated for 10,000+ hours of operation. I know several owners who have installed booster pumps, and all are happy with the results.



(2) If you would like the VENTING SYSYEM in your Pantera to function automatically (so you don't have to vent it manually) convert the expansion tank to a header tank and plumb the system vents to the header tank. Very little modification is required to make the vent system functional, the tanks appear to have been originally intended for this purpose. The revised plumbing mimics the standard vent system installed in racing cars, and in modern passenger cars too. Feedback from owners who have performed this vent system modification has ALL been positive. Here's a diagram displaying what to do:

• Use 1/4" hose for the radiator vent and swirl tank vent
• Use 1/2" hose to connect the "header tank" to the water pump suction
• The Edelbrock and Flow Kooler coolant pumps have two 3/8" NPT ports that can serve as the connection to the header tank
• The header tank, should be clamped in the mounting strap at a height making its mid-point approximately the same height as the highest point in the coolant system. I assume the highest point is the top of the "system tank" aka "swirl tank". Cutting a hole in the cover above the header tank, the same as the OEM hole found in the 1974 models, makes this easier to live with, because the pressure cap on top of the header tank will be accessible through the hole. Cutting the hole in older Panteras is covered in TSB 11, page 3.
• When filling the coolant system, it is best to "top-off" the cooling system when it is hot but with the pressure cap removed (zero pressure on the pump suction), under those conditions the coolant level in the header tank should be no more than half full.

If the tanks are not modified to make the vent system functional, a drain-cock should be installed in the top of one of the radiator's tanks where the fitting for the vent would normally be installed, thus making it possible to periodically vent air from the top of the radiator manually.

Behavior of the Re-Designed System

• The header tank provides a low pressure "dead spot" where air from other pressure zones can be collected and remain trapped (i.e. isolated), preventing the air from making its way back into the cooling system. This keeps the air out of the radiator where it would otherwise naturally tend to collect. This is why the top portion of the header tank should be physically higher than the highest part of the closed loop cooling system. Basically a big air bubble collects in the top of the header tank and has nowhere to go. Air is compressible, fluids are not; therefore the air space in the top of the header tank doesn't change significantly as air collects.
  
  
• Besides providing a place to collect air the header tank serves a second purpose, it allows for the expansion and contraction of the coolant as it heats up and cools down. It replaces the recovery tank. A recovery tank is not necessary because air is compressible, the air space in the header tank allows for the coolant to expand and contract as it heats and cools. The Pantera's converted recovery tank (i.e. the new header tank) does not have a large surface area, but it is very tall, this compensates for the lack of surface area. When used as a header tank the level within the tank shall change a bit as the coolant heats-up and cools-off, but the change in level is not drastic.

(3) A WIRING REVISION for the fans and their controls, should accomplish 3 things:

• Remove the load of the fan motors from the ignition switch
• Eliminate the possibility of motor run-on caused by the fan motors
• Enable the fans to cycle off and on as needed instead of running continuously

It appears the Pantera's radiator fans have always run continuously in the factory installation and in the typical aftermarket installation as well. There is no purpose for this however. If radiator fans run constantly this indicates the coolant never becomes cool enough to reset the fan switches. This could be caused by a cooling system with mechanical issues causing the thermostat to operate wide-open, or this could be caused by fan switches with reset settings which are too low for the thermostat. Assuming the cooling system has no mechanical issues which cause the thermostat to operate wide-open, the fans should turn-off completely when the vehicle cruises non-stop at typical cruising speeds. If the reset settings of the fan switches are too low to allow this then fan switches with higher settings are obviously needed to cycle the fans.

My solution to resolve the issue of the Pantera's constantly running fans is to control both fans with one fan switch so the fans will turn off and on simultaneously; the fan switch shall have a very specific temperature setting allowing it to start and stop the fans in the middle of the operating range of the thermostat. The mid-point of the fan switch operating range should therefore compliment the mid-point of the thermostat's operating range as closely as possible. The fan switch should be located in the radiator's inlet tank (the lower tank) so as to sense the coolant temperature regulated by the thermostat. This solution, as well as solutions for the other two fan circuit problems are reflected in the wiring diagram below.



The mid-point in the operating range of a 192°F (89°C) thermostat is 94°C (fan switches are rated in degrees C). Therefore a fan switch rated at 97°/92° shall best compliment a 192°F thermostat.

The mid-point in the operating range of a 180°F (82°C) thermostat is 87°C. Therefore a fan switch rated at 90°/85° shall best compliment a 180°F thermostat. I have been unable to source a fan switch with M22 threads rated at 90°/85° however, switches with a rating of 92°/87° are the closest I've found.

These considerations are reflected in the switches I've recommended below. Here's the part numbers for name brand fan switches with M22 threads:

Manufacturer...Part Number.........Switch Setting........Thermostat
Intermotor......50190..................100°/95° ..............195°F (91°C)
Intermotor......50104..................97°/92° ................192°F (89°C)
Intermotor......50200..................92°/87° ................180°F (82°C)
Wahler...........823.959.481.F ......92°/87° ................180°F (82°C)

Maintenance:

If you do not perform the vent system modification explained earlier, then you shall need to manually vent air from the top of the radiator as a regular step in maintaining your Pantera. To make this possible a drain-cock should be installed in the top of the raidator's tank where the fitting for the vent would normally be installed.

Fill the cooling system with a 50/50 mix of green Anti-Freeze and water that has had the calcium and magnesium removed. Calcium and magnesium are the minerals that make water "hard" and create mineral deposits and scale. You don't want mineral deposits or scale in your cooling system. If your tap water is naturally low in mineral content you are lucky, go ahead and use your tap water. If not, you'll find several types of water on the market; softened water, carbon filtered water, reverse osmosis water, distilled water, deionized water, double distilled water, high purity water and ultrapure water. Unfortunately the information regarding what type of water to use in a radiator is confusing and contradictory. The ionic state of water is manipulated by any water treatment process; water with an imbalance or depletion of ions can possibly corrode or pit the metal in your cooling system, resulting in pinhole leaks in the radiator core or heater core, so you want to avoid using water with an imbalance or depletion of ions. The chemicals in anti-freeze and coolant treatments are formulated to control some of these problems, but those chemicals are depleted with age and use, so I believe it is wise to fill the system with the best water possible to begin with, the best water being water that will not leave deposits or scale in the cooling system and will not corrode or pit the metal in the cooling system either. Norosion claims softened water is the safest to use, as the calcium and magnesium are removed via an ion exchange process, so the water is not left in an ion depleted condition as it is with other processes. For this reason I place softened water at the top of my list. Reverse osmosis water and distilled water (single distilled) would be the second best choices. Reverse osmosis water and distilled water are normally fed into a deionizing resin bed to produce water labeled deionized, demineralized or high purity. Double distillation is another process used to produce high purity (aka ultrapure) water. Until I learn otherwise I have decided to avoid water labeled deionized, demineralized, double distilled, high purity or ultrapure.

Ron Davis recommends using pre-mixed coolant, i.e. the coolant you buy by the gallon that is already mixed with water. That way which type of water to use (and other chemistry issues) become non-issues.

Other cooling system details include making sure the engine to chassis grounds are clean and tight, and using a coolant treatment like RMI-25, Red Line Water Wetter or Norosion HyperKuhl Super Coolant (blue). The coolant will become corrosive with age and use, this is why the cooling system should be drained and refilled with new coolant every 18 to 24 months unless your coolant treatment specifies otherwise. For instance, Norosion claims if you add their treatment every 12 months you can extend the coolant service interval to 5 years.

The speed of a DC motor is dependent upon the voltage applied to the motor, if full voltage is not applied to the cooling fans they will not run at full speed or move air at their rated capacity. It is imperative to keep the wiring connections to the cooling fans clean and tight to prevent voltage drops across high resistance connections.

Reading: If you want to read more about the design of cooling systems like the Pantera's, refer to Carroll Smith's three books: Prepare to Win (page 122), Engineer to Win (page 170) and Tune to Win (page 97).

-G