As smoke billows from your hood, you look down at your gauges to see the needle pegged in the red. Your engine is overheating because something in your cooling system has failed. In the final episode of David Dissects, I take apart and dive into an entire engine cooling system out of a junkyard Jeep Cherokee.

The purpose of your vehicle’s cooling system is to make sure your engine doesn’t damage itself by overheating. All of those combustion reactions in your cylinders are exothermic (i.e. they produce lots of heat), and if the vehicle in unable to transfer that heat away from the block, your engine will begin to warp, and your oil will be unable to provide enough protection to prevent your engine from quickly wearing and eventually seizing.

As far as cooling system parts go, the water pump is arguably the most important. It’s what gives your coolant motion, sending the ethylene glycol-based fluid through the engine, thermostat housing, radiator, heater core, and all other tubes, hoses and passages in the system.

All vehicles’ engines are cooled via some form of convective heat transfer, but almost all modern cars use ethylene glycol-based liquid antifreeze as the operating fluid. This fluid, with its high specific heat, very high boiling and low freezing point, is pumped through your engine via a water pump (which is spun by your engine’s crankshaft-driven accessory belt).

A wax element thermostat. The wax in the copper capsule pushes a little piston against the thermostat casing. This then pushes the capsule back against a spring, which opens the thermostat valve (you can see boiling water through the open valve).

When the engine is cold, the water pump cycles the coolant through the block, head, and heater core (so you can have cabin heat). Once the engine reaches about 200 degrees Fahrenheit, wax in a thermostat expands and opens a valve, allowing coolant out of the engine and into the radiator.

The coolant runs through the tubes of the radiator, and heat is transferred from the coolant to the tubes and then to the fins. The fins, with their high surface area, allow for high convective heat transfer to oncoming airflow (which is aided by cooling fans that suck or push air through the radiator). Thus, by the time coolant reaches the other tank of the radiator, it’s cooled down significantly. That cold fluid then goes back into the water pump, and cools off the engine.

This cross-section of a radiator shows the two rows of tubes through which coolant passes as it transfers heat to the fins.

Watch the video for a closer look at the viscous fan clutch, electric fan, coolant recovery bottle, engine cooling jackets, and all the other exciting cooling system-related components that you spend your nights dreaming about.

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About the author

David Tracy

Writer, Jalopnik. 1979 Jeep Cherokee Golden Eagle, 1985 Jeep J10, 1948 Willys CJ-2A, 1995 Jeep Cherokee, 1992 Jeep Cherokee auto, 1991 Jeep Cherokee 5spd, 1976 Jeep DJ-5D, totaled 2003 Kia Rio