An internal combustion engine creates a large amount of heat. Much of the heat goes out of the car through the exhaust system, but a great deal is still absorbed by the engine. Your engine runs best when it is warm, but if things get too hot, the pistons can weld themselves to the cylinders and that's the end of the engine. The cooling system is responsible for allowing the car to warm up to the correct working temperature and for maintaining that temperature.

The radiator cap has two functions. First, it is a "lid" for your radiator. Second (and more important), it is designed to hold the coolant inside the cooling system at a pre-determined amount of pressure. Liquids under pressure take a longer time to reach their boiling points. If the radiator cap did not keep the liquid coolant under pressure, all of the coolant would boil away, leaving your cooling system dry and your engine un-protected from the heat.

The radiator is designed to dissipate the heat that the coolant has absorbed from the engine. Radiators are filled with tubes that the coolant passes through. Airflow from outside of the car and the fan carries heat off of the radiator. The coolant enters the receiving tank at the top of the radiator, passes through the tubes inside, losing the heat it has collected, then collects in the dispensing tank at the bottom for the water pump to circulate it back through the cooling system.

The coolant goes into the radiator to dissipate the heat that it collected in the engine. The heat is drawn off by air passing through the radiator. If the car is not moving fast enough to push air through the radiator, the fan will come on and pull the air through. The fan is usually mounted on the water pump shaft and is powered by the same belt that runs the water pump. Running the fan takes power from the engine, so it's only turned on when it is needed. The fan is controlled by a thermostat switch that tells it when the temperature has risen to a point where the fan is needed.

The water pump forces coolant to circulate through the engine block.

Coolant flows from the engine block back to the radiator through the upper radiator hose. This hose is blocked by the thermostat valve unless the temperature is high enough to allow the valve to move and let coolant through. Hoses are made from flexible rubber with either spiral wire embedded in them or fabric reinforcement. Hoses vary in size according to engine specifications. There are three types of hoses used in most vehicles: Straight, pre-bent, and accordion.

The job of the cooling system is to allow the engine to warm up to its optimum working temperature (between 180 and 200 degrees F) and then maintain that temperature. The thermostat regulates the temperature of the engine. It sits between the engine and the radiator and has a temperature sensitive valve that prevents coolant from entering the radiator when the temperature is too low. The valve recycles warm coolant through the engine block until it reaches the right temperature. At that point, the valve opens and the coolant enters the radiator to begin dissipating un-needed heat.

The coolant in a car must be able to hold the heat from the engine then release it in the tubes of the radiator. Water is excellent for holding heat, but it freezes to readily to be an effective winter coolant in most places. The addition of antifreeze to the water significantly lowers the freezing temperature of the coolant. It also raises the boiling point, reducing the risk of boiling the coolant out of the system. The main ingredient in most standard antifreezes is ethylene (EG), most also add ingredients to prevent rust and corrosion in the cooling system.

The heater core is a mini-radiator that keeps your car warm when it's cold outside. The heater core is mounted under the dash of the car. It works on the same principle as the radiator (coolant flows through tubes inside it and releases heat into the air being forced by the tubes) but the heater fan blows the heat into the car instead of out of it. The heater core draws heat off the engine, so if your car is running a little hot, turning the heat on can help reduce heat in the engine until you can get to a mechanic.

The heater fan blows air through the heater core into the cabin of your vehicle. It is activated by the controls on the dash board.

The engine block and cylinder head are manufactured in one piece with precast "Water Jackets", or passages for coolant. The water pump sends the coolant into the water jackets where the coolant absorbs the heat from the engine before returning to the radiator.

The lower hose carries the coolant from the dispensing tank to the water pump. Hoses are made from flexible rubber with either spiral wire embedded in them or a fabric reinforcement. Hoses vary in size according to engine specifications. There are three types of hoses used in most vehicles: Straight, pre-bent, and accordion.