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.
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).
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.
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.