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I apologize for starting yet another thread on cooling, but a quick search hasn't found anything specifically on this topic.

Stock coolant piping has hot engine coolant entering the bottom of the radiator and exiting from the radiator top hose.

I am installing a double pass Ron Davis radiator into 2511. Supplied by Dennis Q, the inlet tank has two threaded bosses for temperature sensors. There are no threaded bosses in the outlet tank. See photo.

In talks with Jon Haas regarding his EIS engine control box, he told me he strongly believes the fan temperature sensor should be sampling at the outlet instead of the inlet.

To do this would require the addition of a threaded boss on the outlet tank or the use of an in-line temperature sensor housing spliced into the coolant return line. Either approach is fairly easy to create, but I would lean to adding the threaded boss instead of adding two more hose clamp areas on the coolant piping.

Ron Davis offers two sensors, one turns on at 185° and off at 165°. The other turns on at 195° and turns off at 175°. There are aftermarket sensors with different ratings, one I have seen turns on at 200° and turns off at 185°.


Is the inlet or outlet tank the best place for a fan temperature sensor?
Could they both be acceptable if fitted with the "correctly" rated temperature sensor?


What sensor rating should be used if installed in the inlet tank?
Conversely, what sensor rating should be used in the outlet tank?


Engine thermostats are readily available in 160°, 185° and 195°. Is the thermostat temperature rating dependent on the fan sensor rating?

I am leaning to installing:

180° engine thermostat
195° fan temperature sensor in outlet tank

Please share your comments, wisdom and suggestions.



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Mr.Davis is correct. Install the temperature control switch in the inlet of the radiator or the outlet of the engine (practically the same temp). This is the proper place for the feedback to originate, considering you're attempting to regulate the temperature of the coolant exiting the engine block.

This way the fans are working in conjunction with the thermostat, both attempting to regulate the temperature of the coolant exiting the engine block.

I've answered the other questions in sticky #2.


Originally posted by George P:

... 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 ...

... 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)


To understand the engineering behind the selections, you have to understand the operating characteristics of the two devices.

An 82°C thermostat (180°F):
  • Begins opening somewhere between 78°C and 82°C. Thus a portion of the coolant recirculating through the engine begins flowing to the radiator.
  • Is open midway somewhere between 85°C and 89°C (87°C is the mid-point within the range of mid-points). Unique to the 351C in its day, coolant bypassing the radiator and recirculating through the engine is blocked-off at this point.
  • Is fully open somewhere between 92°C and 96°C. At this point the maximum amount of coolant is capable of flowing both through the engine and to the radiator. But the actual flow rate is limited by engine rpm because the coolant pump is crankshaft driven.
  • Has an operating range spanning 14°C on average.

A fan control switch rated 92°/87°:
  • Starts the fan(s) at 92°C, the earliest possible temperature the thermostat may reach full open. For the coolant to have reached this temperature even though the thermostat is almost fully open, it is obvious that the amount of coolant flowing is insufficient to handle the engine's heat load.
  • Stops the fan(s) at 87°C, when the thermostat is once again in the middle of its control range, and coolant temperature is once again capable of being controlled via modulation of the coolant flow rate.
  • Has an operating range spanning 5°C, 36% of the operating range of a thermostat. Thus the fan switch can operate "within" the operating range of the thermostat.

Thus the fans "start" only when the heat load overwhelms the cooling system's ability (via the thermostat) to control the temperature of the coolant without their assistance, and the fans "shut-off" when conditions return to normal, and the thermostat is once again operating in the middle of its range.

Last edited by George P

I had the same question so I called and spoke with one of their techs. Long story short, not too impressed with his understanding of a Pantera cooling system. I knew I was basically not going to get any valid information when he started explaining the need for two 24Amp Spal fans in order to ensure enough airflow to overcome all the heat added by the air conditioning condenser. Eeker

Then he started in on the proper location for sensors needed to feed Data to the car's computer and at that point I basically gave up on the conversation.

I am just trying to determine how best to utilize the items that I have, and the proper temperature ratings for the thermostat and fan sensors.

My Ramblings and Opinions….

The cooling control scheme for all the equipment I worked was to try to set the radiator (heat exchanger) outlet to a design temperature and let the engine outlet indicate how much load was applied.

The original Pantera locations were in the radiator outlet, and fans were set for ~160F and ~180F. thus when the radiator outlet was greater than~160F cut on first fan, and if not enough as indicated by radiator outlet getting greater than ~180F cut on second fan. When the end tank was changed from vertical divide to horizontal is when the switches got put on the wrong (inlet) side.

Thus I would lean towards fans controlled by radiator outlet with the 165F on switch.
1)thermostat controls the engine's coolant outlet
2)fans assist the radator's coolant outlet
3)coolant in to the motor needs to be cooler than thermostat

How hard would it be to swap the under car tubes so that inlet goes to the top? With the radiator outlet out the top has the location where air would accumulate locations the same as the water pumps suction (increases chance of pump cavitation). By having lower radiator supplying the pump provides the most positive suction.

With all that said and the differing recommendations, what is the problem with the fans running all the time? I see them becoming little “wind turbines” and going from using current at low speed to charging the battery at speed.

(sorry for the extreme rambling...just can't get my thoughts together any more)
Last edited by jfb05177
Originally posted by David_Nunn:
Something no one has mentioned: if your radiator fan shroud does not have a baffle in the center, that isolates each fan, you need both fans to turn on at the same time. If only one fan turns on, it will draw most of its air through the large fan opening right beside it, rather than through the radiator.

When fully shrouded fans first came available a few people experienced overheating at sustained high speed due to the fact not enough air could be drawn through the fan opening. This was overcome by cutting out portions of the shroud and replacing with flaps that could self open at speed.

One aspect often overlooked for optimal fan performance is fan blade standoff from the radiator. When I installed a Flex-a-Lite system on my '74 I had to space it off the radiator to obtain the 3/4" recommended.
Larry, I have to agree with Jon on this. The fans are to “assist” the radiator in cooling. There are times where the radiator cools enough on it’s own (highway cruising) and no need to run the fans. When radiator alone doesn’t cool enough, the fans then kick in to assist. With the switches on the inlet, they would run in conjunction with the thermostat and run anytime the thermostat opens up (assuming they are matched at temp). I suppose this would be beneficial if you were on the track running high rpm for extended periods, but for normal driving I don’t want my fans running any more than necessary.
Supplemental to Julian's post, I once built a fan shroud on the backside of a good-condition stock radiator, using two 10" blade flat sucker fans. On a trip to 'Vegas across our lonely desert highway, I ran our car up to 150 mph and held it there for ten (10.0) full minutes. The water temp slowly climbed from it's usual 190-200 degrees F to 230 degrees F, where I quit. After several more minutes at 80-90 mph, the water temp slowly returned to 'normal'.

Several years later after changing to a better aluminum Fluidyne rad and bigger shrouded 12" Flexilite sucker fans, I repeated the test; the high speed temp climb did not happen- at least at a sustained 150 mph. Better rad? Bigger fans with larger holes in the shroud? Both? Not sure.
I use an old aluminum Weiand (8209?) water pump with no warm-up recirculating port, and straight impeller modified for a welded ss backing disc. Pump is 20 yrs old & much modified. The change did NOT lower running water temps with a stock rad. In fact, I have a whole list of things covering the entire cooling system that did NOT change the water temp. during highway cruise. The only thing that DID lower it was the Fluidyne radiator w/Flexilite sucker fans.

And for still-unexplained reasons, I only get about 1-2 yrs out of a thermostat (either Windsor or Cleveland-types, stock or aftermarket) before it begins sticking & needs replacement.

Originally posted by Bosswrench:

... And for still-unexplained reasons, I only get about 1-2 yrs out of a thermostat (either Windsor or Cleveland-types, stock or aftermarket) before it begins sticking & needs replacement ...

Exposure to high temperatures resulting from the lack of coolant circulation during warm-up?

Why not restore the cooling system to original functionality and see if the thermostats last longer?
Exposure to high temperatures resulting from the lack of coolant circulation during warm-up?


What "high temperature" ??

Whether or not the original recirculation passage is functional does not increase the temperature of the water that the thermostat sees. While without recirculation there may very well be hot spots created in the engine block, the thermostat does not sense engine block temperature. In either case, when coolant temp reaches the thermostat rating the water will start to flow to the radiator.

Always open to learning, but I do not see where a thermostat is subjected to any "high temperature" regardless of whether the coolant is or is not recirculated during the warm up period. Thermostat can only get so hot and then it will open.

Lots of good opinions and insights. I agree with John to install sensor after radiator. I only want my fans running if the radiator is no longer up to the task of meeting my target temp.

I install my sensor on an extra threaded inlet on my waterpump. That reads the temp of fluid leaving the radiator before being pumped into the block. Depending on the model waterpump you purchased, it may not have an extra threaded input. One may drill and tap another input if proficient.

An alternative approach would be to reverse the flow on your radiator so the already installed sensor bosses are on the outlet side. I don't believe flow direction materially matters on a cooling system with adequate capacity.

I would tune your thermostat and sensor choice to get your oil temps closer to the 220 degree range. My experience running a cooler engine was that I was not getting the oil temp into the 220 degree range. I recognize on these lists that bragging rights seem to go to the owner with the lowest cruise coolant temp. However, cylinder bore wear is more aggressive at these lower temps and power output is increased with oil temps in the 220 degree range. Although, I started with lower temp fan switches and thermostats, paying attention to oil temps has modified my approach raise these temp settings to get back more heat. If you pay attention to oil temps, as the two coolant and oil temps)are related, you may find it beneficial to raise your coolant fan sensor temp and thermostat temp. I use a 195 degree switch because it was the highest I was aware. My oil temps are still to cool.

Summary, monitor your oil temps and adjust from there.

It's interesting reading about the placement of the fan temperature switch/s. Unfortunately my just purchased L is a mess cooling system wise. Fans run all the time, why, well turns out there is no place for fan switches in the rad!! Bleeder from the rad goes to the rear of the car but is not hooked up to the swirl tank!! Non Cleveland thermostat is fitted. Thankfully I had only driven it 12 miles before I found these issues.

I'm keeping things simple and have used this fan switching system successfully previously. Whether with or without an electric fan just about ALL engines primary temperature control is via a thermostat placed at the outlet of the engine block. This is "real" engine temp. So for the fan switch, it follows that the ideal position is similar. eg. Thermostat housing or radiator inlet. On my Pantera it will be placed in the vacant 3 port vacuum switch position in the water pump, that "Ford" often uses to monitor engine temperature. Remember Ford uses that position to switch vacuum to the distributor vac advance to speed up the engine to increase fan speed on various front engined cars with belt driven fans if the engine starts to overheat. So it works for temp sensing!

I have two other front engined Fords where I switch the electric fans (originally belt driven) from a switch mounted in the thermostat housing treaded port. Our cars do not have that facility, hence the vacuum switch position. (I believe this position still measures similar temp values to the outlet of the thermostat). Quite simply, it works on my other 2 cars. I will probably use a 92 deg C / 87 deg C switch. Thermostat will be a 77 deg C cleveland type, bleed hose will be fitted to the inlet pipe of the water pump. Standard type overflow tank is fitted. Oh and if the fans don't control the temp early enough or or to late, I'll change the fan sensor switch to a different value. I'm 95% confident this will work, as it has in my other cars. The only issue may be the standard fans. The rad is brass and looks real good, but I'll be also adding a water strainer/filter. I will definitely let you know what the result is. (good or bad)

I have never understood why you would want to measure the returning coolant temp to control fan switching/engine temperature. It's simply well and truly after the fact, so to speak!!

Last edited by gt-pilot

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