Thermostat

The 351-C, 351-M and 400-M engines all require a thermostat that has a copper nose or thimble attached to the base. This attachment protrudes into a matching hole in a brass disc (351-C) or in a casting (M-series) below the thermostat. The hole is a radiator bypass to promote fast warm-up. Using any thermostat without the protrusion will permanently allow up to about 25% of the cooling water to never pass thru the radiator and will result in overheating. The only exception is if you run certain aftermarket aluminum water pumps which do not have a matching passage, so the warm-up feature is disabled. Rear 351-C thermostats come in a limited number of temperature ranges, unfortunately. But testing has shown that in Panteras, the thermostat does not set the engine tempoerature- adding a 160 thermostat will NOT lower your engine temp, for instance.

Yes, there is a special thermo. Without it your engine will run hot because of the by pass. I spent a lot of time and money hunting down my overheat problem. It ended up being the $4.00 thermo.

Thank you Jack! I do in fact have an aftermarket aluminum waterpump that I purchased through Hall and the thermostat I received did not have that nose you have just described. I do however have the bypass plate still within the block. Do you think the water fully circulate to the radiator?

If the pump's installed so you can't see if there's a bypass passage or not (Weiand is the only one I know for sure doesn't), the only way to be sure is to tap a 3/8" freeze plug into the brass washer hole underneath the thermostat. This absolutely plugs the recirculation passage and allows you to run any thermostat at all. My Pantera is done this way & I use one marked 'Ford 289'. To remove the freeze plug later on, drill a 1/8" hole in it, run a long sheet-metal screw in the hole a few threads & pop the plug out with a pair of screwdrivers or pliers.

The Cleveland thermostat looks like this: http://www.geocities.com/provamo72/Cooling_6.html

Bottom of page.

Chuck

Thanks again Jack! I will look into this this weekend!!!

Jack one last question... I can not locate a 3/8" Brass freeze plug? I can however find a Steel one? What are your thought with using Steel vs. Brass?

Steel freeze plugs will rust out in ten years or so.... Its much more serious in the sides of the block than under the thermostat, as you can only access one of the 6 in your block with the engine in place. I'd say it'll be OK up there.