Barir's World

How It Works: Cooling Your Engine

A coolant pump, or water pump, circulates the antifreeze and water mixture between the engine and the radiator. After the coolant circulates through the engine, the pump pushes it out the upper radiator hose into the radiator, a heat exchanger made of metal tubes (aluminum on today's cars) to which fins are attached. The fins draw away heat and dissipate it to the air that is drawn through the radiator by fans and the forward motion of the car. The cooled coolant is drawn from the radiator through the lower radiator hose and back into the engine by the pump, and the cycle starts all over again.

When the engine is cold, coolant circulates only within the engine, so engine heat warms it up faster. At about 195 degrees F, the coolant heats a temperature-sensitive valve (the thermostat) that opens to allow the coolant to flow through the radiator. The thermostat may be located at the engine outlet, in line with the upper radiator hose, or at the inlet to the water pump (the preferred location on today's cars).

The coolant also flows through hoses into and out of the heater, which, like a miniature radiator, gives up its heat to the surrounding air. In this case, however, the heated air is blown into the passenger compartment.

Raising the cooling system's pressure also raises the coolant's boiling point, so the radiator cap (which also could be on the engine or on the separate reservoir) has a pressure valve to raise the pressure in the cooling system by about 15 psi. This increases the boiling point of the coolant by about 40 degrees F. So, the boiling point of a 50/50 mix of antifreeze and water in a properly functioning system is about 265 degrees F or higher.