Marlin Jack - Also machines the correct steering rack spacers in Stainless - I bought both (restrictor and steering rack spacers from him)

Greg

quote:

With the passage closed, coolant circulates poorly through the block and heads and you can get hot spots, maybe even "steam pockets".

Hmmmm?

Someone else feel free to jump in here, but I've always thought blocking off the passage only resulted in a slower warm-up time for the engine.

I mean, when the coolant gets hot, the 'hat' blocks off the passage, right? The same as an owner blocking the passage, right? I doubt Ford designed in that event if it would result in poor circulation, steam pockets or hot spots.

Larry

Thanks for the info. The reason I was asking is that I have been running without a thermostat for about 3000 miles. I will be changing all my hoses, as well as installing a new thermostat.

On the robertshaw t-stat exactly what part of the thermostat is the 'HAT'. Chuck

Now that it is 107F in Nor Cal, this age-old question has come up again. I have never seen an explanation on this forum about exactly "WHY" we need a special thermostat for a Cleveland, so here is my explanation:


Here is how it works; Most cars, Chevy, 351 Windsor etc., the thermostat opens and closes, and that's all. It lets water out to go to the radiator, or holds it in the motor and heater hoses to get warmed up.

On the Cleveland, the thermostat opens to let water out, AND AT THE SAME TIME, the "hat" or "foot" moves down and plugs the bypass hole. If you run a regular (351W) thermostat, the bypass hole is always open, allowing a large portion of water to just recirculate in the block instead of being pushed all the way up to the radiator. This lets the motor overheat, even though the radiator never got hot.

This is why you need a special thermostat.

Jay Morris

...First, I Thank-You George and Curt for the 'Vote of confidence'! Jay M. is Exactly Correct! But forgot to mention that when the Correct Thermostat opens to seal the Bypass Port, it needs to seal against the 'Bypass Restrictor Plate'. If this plate is missing, then the remaining counterbore will be way too large to effect a closure. These Restrictor Plates are available at this very moment on Ebay Motors. At a cost of $35.00 ea. with $5.00 Shipping. If You should miss that oportunity You may contact Me anytime at the email address that Curt has listed above. I Thank-You All!! Marlin.

...To answer You original question; running with-out a thermostat causes the Engine to overheat because the Coolant is NOT allowed to spend Enough time within the Block in order to Absorb enough Heat! The coolant Is pump through the block TOO fast! Trust Me, I have Also, tried it! Normally the Thermostat will 'Hold' closed and keep the (already cooled from the Radiator), coolant 'captive' in the block until it 'picks-up' enough heat and NEEDS to be sent back to the radiator! The 'Baypass' System itself, Insures that the ricurculated coolant through the Block, Travels directly Past the Thermostat 'Pot'! Does this answer Your question? Marlin.

What part of the thermostat is refered to as the 'HAT'? Is it the cup that comes down or the small piece on the bottom of the cup? Marlin what size hole does your restrictor plate have? Iam going to replace my t-stat this weekend and want to know what to look for. Thanks Chuck

...The central hole is held to Between, Min. .725" and .750" Max. Marlin.

...A word about the Aluminum Water Pumps, such as the Weiand 8*09 Don't remember the exact number. These amoung Others Do NOT have the 'Bypass'(passage)cast into them. Probably the One reason why they Claim a '30 Per-cent Increase in flow'! Yes! To the Radiator! But NO recirculation through the block, so this causes UNeven Warm-up (although, this can be remedied by simply turning on the Hot Water Valve for the Heater Core); This will allow a 'recirculation Bypass' from the block through the Heater and Back to the WaterPump, and through the Block, again! What I did, was to Clamp the W. Pump into an Angle Vise on the Mill table at the Exact angle, and Milled the By-Pass Passage with a 5/8" End Mill. The sides were Close! But the Problem was Corrected!..... And the 5/8" size reminds me of the ACTUAL passage even below the so called 'restrictor Plate'; which is between 5/8" and 3/4"!! Indicating to Us that these Brass Plates are NOT so much Important as a Restriction as they ARE Very Important as a SEAT for the Thermosatat to SEAT Against, when the Thermostat Opens, effecting a NEAR complete Closure! Marlin.