The engine runs best when the coolant is about 200 deg F. It is at this temperature that:
• The combustion chamber is hot enough to completely vaporize the fuel. It provides better combustion and reduces emissions.
• The oil used to lubricate the engine is thinner, therefore the engine parts will move more freely and the engine will waste less power moving its own component around
• The metal parts will wear less
You will find that vehicles have two kinds of cooling systems:
In a liquid cooled cooling system, the vehicle circulates a fluid through pipes and passageways in the engine. As this liquid passes through the hot engine it will absorb heat, and this then cools the engine. When the fluid leaves the engine, it will pass through a exchanger, or radiator, which will transfer the heat from the fluid to the air blowing through the exchanger.
With an air cooling system, it is not often that you will find many modern vehicles with this system. Instead of circulating fluid through the engine, the engine block is covered in aluminum fins that conduct the heat away from the cylinder. A powerful fan will then force the air over the fins, which then cools the engine by transferring the heat to the air.
There is a lot of plumbing involved in the cooling system. The pump sends fluid into the engine block, where it makes its way through passages in the engine around the cylinders. It will then return through the cylinder head. The thermostat is located where the fluid leaves the engine, and the plumbing around the thermostat will send the fluid back to the pump directly if the thermostat is closed. If however, the thermostat is open, the fluid will go through the radiator first and then back to the pump.
On vehicles with automatic transmissions, there is normally also a separate circuit for cooling the transmission fluid build up into the radiator. The oil from the transmission is pumped by the transmission through a second heat exchanger inside the radiator.