Re: USINGATHERMOSTAT.......OR NOT?

Posted by Bob Bidonde on April 16, 1998 at 08:30:30

In Reply to: USINGATHERMOSTAT.......OR NOT?
posted by Ken Smith on April 15, 1998 at 15:30:24

An "Achilles Heel" of the Model A & Model B engines is that the water pump is in the wrong position in the system - at the top of the water supply and should be at the bottom to assure the impewller is always submerged. Moreover, the larger diameter hose should be at the inlet side of the pump and the smaller diameter hose at the outlet side of the pump - they are backwards in the Ford design. As a result, Model A & B water pumps tend to cavitate and foam the coolant when the coolant level is at or just below the baffle in the upper radiator tank. This is often mistaken as overheating when it oozes out of the radiator cap. If the coolant level is kept high (topped off above the baffle), then the pump produces more coolant flow than the radiator can accommodate and coolant goes out of the overflow pipe and leaks out at the radiator cap. One major benefit of a thermostat in the outlet hose is that it restricts the pump output flow and keeps the pump impeller submersed in enough coolant to prevent cavitation (foaming). This is beneficial as the engine temperature becomes more constant in the process. So a thermostat is definitiely good, and in your case, I suspect the thermostat you removed was preventing pump cavitation (foaming of the coolant).
1928 & '29 Model As run hotter than later models, so I recommend the 160 degree thermostat. 1930 & '31 Model As have larger radiators and can easily handle 180 & 190 degree thermostats. High compression heads tend to make Model As run cooler and in this case, use the 180 or 190 degree thermostat. In my experience with both stock and modified Model A & B engines, the thermostat with the stainless steel tubular sleeve is most durable and will not tumble in the hose.Place the thermostat up at the radiator end of the outlet hose. I am currently running 180 thermostats in my '31 Coupe with a modified Model B engine and in my Victoria with a stock Model A engine. These cars are often driven at 55mph or more and they do not overheat or foam.
I have found that many cooling system additives cause the coolant to faom regardless of pump cavitation. So I do not recommend anything other than a good brand of antifreeze (50/50 or 60/40 antifreeze to water mixture) go into your cooling system. Good antifreeze has all the additives already in it. I use Prestone in both my Model As.
No cooling system discussion is complete without a warning about original 2-blade fans. Don't run one even if you think it looks new or has been restored. They tend to throw a blade from metal fatigue which cannot be measured or inspected. Thus a perfectly good looking and or restored original fan could throw a blade just as easily as a ratty looking one. Typically the blades pierce the hood, puncture the radiator and cutup the fan belt. Figuring $300 for a new radiator, $500 to fix the hood, and $250 for the flat bed truck ride home, it is a lot cheaper and safer to run a brand new fan (zero fatigue life expended). I run Dave Wilson's plastic fan with very goog results, and I recommend the various plastic replacement fans over the metal ones.

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