That's because the early two-cylinder tractors don't HAVE them! The cooling system is best described as a "thermal siphon" or "gravity" system. Take a look at this cross section of the front end of an early Model D. |
The hot water rises out the top of the engine (Red arrow) and into the top of the radiator. It gets cooled by the fan and sinks to the bottom of the radiator (Green arrow) to flow back into the bottom of the engine to replace the water that is leaving at the top. There's NO water pump in a thermal siphon system. The only "thermostat" is the operator, who controls the temperature by manually opening and closing the shutters in front of the radiator. This system worked quite well for many many years in hundreds of thousands of tractors. |
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