A cooling system has several functions. It must remove excess heat from the engine，maintain a constant engine operating temperature, increase the temperature of a coldengine quickly, and provide a means for warming the passenger compartment.
Removing engine heat
Burning air-fuel mixture produces a tremendous amount of heat（up to 2，5000C），which is enough to melt metal parts. Some combustion heat is used to produce expansionand pressure for piston movement. Most combustion heat flows out with the exhaust gasor flows into the metal parts of the engine. Without removal of this excess heat，the engine would be seriously damaged in a matter of minutes.
Maintaining operating temperature
Engine operating temperature is the temperature the engine coolant reaches undernormal running conditions. Typically，car engine's operating temperature is between 800C and 1000C．
Reaching operating temperature quickly
An engine must warm up rapidly to prevent poor combustion, part wear, oil contamination, reduced fuel economy, increased emissions and other problems. Forinstance, the aluminum pistons in a cold engine will not be expanded by heat，which causetoo much以earance between the pistons and the cylinder walls. The oil in a cold enginewill also be very thick，which reduces lubrication and increases engine wear. The air-fuelmixture will not vaporize and burn as efficiently as in a cold engine.
Heater operation
A cooling system commonly circulates coolant to the vehicle's heater. Since the engine coolant is warm, its heat can be used to warm the passenger compartment.
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