The first 2,447 Model T engines were cooled with water pumps.
Early Model T engines used a mechanically driven water pump to circulate coolant. Ford soon abandoned that component in favor of thermosiphon cooling, a simpler system that relied on natural circulation caused by differences in water temperature and density.
With thermosiphon cooling, hot coolant rises from the engine into the radiator. As it cools, it becomes denser and descends, returning to the engine without requiring a pump. Removing the pump reduced cost, simplified the engine, and eliminated a component that could fail or require maintenance—priorities that fit Ford’s emphasis on durable, inexpensive mass transportation.
The figure 2,447 refers to engine or unit numbers, not a production year or a percentage of all Model Ts. From unit 2,448 onward, thermosiphon cooling was generally used, although a few exceptions existed before roughly unit 2,500. The change also explains why early surviving cars can differ mechanically from later examples, even though all are recognized as Model Ts.
Thermosiphon cooling worked well for ordinary driving, but it could be more vulnerable to overheating under unusually heavy loads or severe operating conditions.