Basically, there are two types of cooling systems available on motor cars. First is the Liquid cooled and Air cooled. Air cooled engines are available on a few older cars, the likes of the original Volkswagen Beetle, the Chevrolet Corvair and a few others. However a good number of modern motorcycles still use the air cooling, but for the most part, however, automobiles and trucks use liquid cooled systems and that will form the focus of this post.
The cooling system is summed up of the passages inside the engine block and heads, a water pump to circulate the coolant, a thermostat to regulate the temperature of the coolant, a radiator to cool the coolant, the radiator cap to control the pressure in the system, and some plumbing materials consisting of interconnecting hoses to move the coolant from the engine to radiator and also to the car’s heater system where hot coolant is used to warm up the vehicle’s interior on a cold day.
The cooling system operates by sending a liquid coolant through passages in the engine block and heads. As the coolant goes through these passages, it picks up heat from the engine. The heated fluid then makes its way through a rubber hose to the radiator in the front of the car. As it flows through the thin tubes into the radiator, the hot liquid is cooled by the air stream entering the engine compartment from the grill in front of the car. Once the fluid is cooled, it goes back to the engine to absorb more heat. The water pump has the duty of keeping the fluid moving through this system of plumbing and other hidden passages.
A thermostat is positioned between the engine and the radiator to make sure that the coolant stays above a certain preset temperature. If the coolant temperature is below this temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine. The coolant will keep to circulating like this until it gets to the required temperature, at which point, the thermostat will open a valve and allow the coolant back through the radiator.
To prevent the coolant from boiling, the cooling system is designed to be pressurized. Under pressure, the boiling point of the coolant is considerably raised. However, too much pressure will cause hoses and other rubber parts to burst, so a system is needed to relieve pressure if it goes beyond a certain point. The job of maintaining the pressure in the cooling system is the strictly the duty of the radiator cap. The cap is designed to release pressure if it gets to the specified upper limit that the system was designed to handle. However before the ’70s, the cap would release this extra pressure to the pavement. Since then, a system was created to capture any released fluid and store it temporarily in a reserve tank. This fluid would then return to the cooling system after the engine cooled down. This is called a closed cooling system.