What type of cooling system did the Model T engine use?

The Model T engine used a thermosiphon cooling system.

Thermosiphon cooling circulates water through the engine without relying on a water pump. As the engine warms the coolant, the hotter, less-dense water rises into the radiator. After releasing heat there, the cooler, denser water descends and flows back through the engine, creating a natural circulation loop.

This design matched Ford’s broader emphasis on simplicity, low cost, and easy maintenance. The Model T still used a radiator and a fan to remove heat from the coolant; thermosiphon describes how the water moved through the system, not the entire cooling apparatus. That is why “radiator fan” and “radiator” are related terms but not the canonical answer.

There is an early-production qualification. The first 2,447 Model T engines used gear-driven water pumps. From engine unit 2,448 onward, with a few exceptions around the transition, Ford adopted thermosiphon cooling. Thus thermosiphon is the standard answer for the Model T’s cooling system, even though a small number of the earliest cars differed.