How cool is cool enough?

[Steve Jelf]

Just for a theoretical discussion I'll make up some numbers. Let's say 50/50 antifreeze keeps my Model T's operating temperature down to 190º. Some folks claim that Product X will lower that to 180º. Is that better? Why? A related question: How cool is too cool?

[John Codman]

I honestly don't know Steve, but my '27 runs at 170 at the top tank of the radiator and it's 117 at the bottom. That's on a 90+ degree Florida day. That's with a 50/50 coolant mixture.

[TXGOAT2]

180 to 200 is fine. Running cooler than 180F invites sludging of the crankcase and carbon deposition in the combustion chamber. A well-worn engine may operate a little better running around 180. A tight engine in good tune would probably rather run about 190-200F, and could be expected to stay cleaner and provide better fuel economy at the higher temperature. Anything up to about 220 F is OK with a clean cooling system, but running hotter than that invites boiling and could contribute to fuel system issues. All this is based on coolant temperature at the water outlet running under ordinary conditions. Extremely hot or cold condtions or very high altitude operation might call for adjustments. If you choose to run a water pump, installing a thermostat at the water outlet is a good idea. A 180 F thermostat of the type that was common up through the 1970s should be good for general use and can be easily adapted without modifying any original engine parts. Drilling a couple of 1/8" holes in the thermostat plate is a good idea. Doing so will allow filling and draining the cooling system easily and will permit a limited amount of coolant to bypass the thermostat when it is closed, which helps assure that hot water will reach the thermostat in a timely manner and will also avoid uneven heating of the engine, which could lead to steam pockets. I don't think a thermostat is needed with a stock system with no water pump. The thermosyphon system tends to regulate itself.