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Cooling Systems: Part 2

How this important system works and helps your engine keep its cool.
» Part 1: Heater Core
» Part 2: Overflow & Hoses
» Part 3: The Cooling Fans
» Part 4: Sending Units

The Heater Core:

The heater core is a smaller version of the radiator that is used to keep your toes warm when it's cold outside. You may have heard the advice that if you car is overheating, turn the heater on full blast with the fan on high. This will cool the engine because the heater system is actually a secondary cooling system that behaves in the same way the main cooling systems works.

The heater core is usually mounted under the dash on the passenger side and is usually incorporated with the air conditioning system. Hot coolant is routed through the heater core through the heater hoses. A blower fan is also mounted there to direct air through the heater core and inside the car. The heater core draws its hot coolant directly from the engine and it returns to the water pump. In this way the heater will work whether the thermostat is open or closed.

Pressure (Radiator) Cap:

The radiator cap acts as more than just a "lid" for your radiator; it keeps your engine cool by sealing and pressurizing the coolant inside it. As the coolant in the cooling system heat up, it expands. As it expands it creates pressure in the cooling system. As the pressure increases, the boiling point of the coolant increases. The radiator cap is a pressure relief valve that controls the amount of pressure in the cooling system. What makes this important is that the higher the temperature of the coolant is, the greater the temperature gap between it and the air temperature is. So a cooling system under a predetermined amount of pressure takes heat away from the engine faster, which makes it more efficient.

This pressure increase can raise the boiling point of the coolant by about 50 degrees. The hotter the coolant is, the faster the heat in it moves to the radiator and the air passing by. When the cooling system pressure reaches about 15 psi, the valve in the radiator cap opens allowing the coolant to leave the cooling system. The coolant flows from the radiator to the bottom of the overflow tank through the overflow tube.

When the cooling system cools down, a vacuum is formed inside the system and another valve inside the radiator cap opens allowing coolant to flow in from the overflow tank. This keeps air that can cause corrosion inside the cooling system out and insures the cooling system is always filled to maximum capacity.

» Part 1       »
Part 2       » Part 3       » Part 4

Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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