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The cooling system in your car consists of the radiator, water pump, thermostat, and various hoses to connect everything to the engine. Coolant, antifreeze mixed with water, circulates by means of the water pump, through the radiator to be cooled. It's then regulated by the thermostat to maintain the proper temperature, allowing it to return through the engine as needed to achieve optimum operating temperature. Depending on your vehicles's manual, the coolant should be flushed as part of a regular routine maintenance routine. Keeping the coolant and the coolant system clean is as important is the coolant itself. 

Modern day engines are designed to much closer tolerances then those of 20 years back. Today the average operating temperature is set to over 200 degrees where in the past it was common to have an engine run at 180 degrees. Most engines are computer controlled monitoring much closer how the engine is running and under what load. 

The temperature is being controlled by the thermostat which will trap the coolant in the engine during initial warm up until it raises to proper operating temperature, then it will open allowing hot coolant to be replaced by cooler fluid from the radiator. Circulation is provided by the water pump and as the coolant in the radiator becomes hot the fan, either electric mounted on the radiator or mechanical on the front of the engine, will engage to bring the coolant temperature back down to the specified temperature.

If you have an automatic transmission there will also be a cooler incorporated in the radiator with steel lines running down to the transmission. Hot transmission fluid is cycled through parallel tubes and cooled to the engine operating temperature. As a side issue the transmission can actually make the engine overheat. If your pulling a heavy load, straining the transmission, or if the transmission is slipping the hot oil, around +300 degrees, will pass its heat through the radiator heating the coolant and raising the engine temperature. What you might think is an engine problem could be a transmission problem

In some engines the warm coolant is also used to preheat the fuel, this is common on diesel engines in particular. Just another example of how the cooling system is actually a temperature regulating system

Branching off the engine block are the coolant lines that come into the passenger compartment bringing heat to the heater core. Air is blown over this small radiator like device bringing the interior up to a comfortable temperature.

Through out the cooling system there are numerous controls, temperature indicators, pressure switches and over flow protection. As usual the more time goes on and technology expands the more complex things tend to become. But one common danger still exists. Never remove the radiator cap on a hot engine, a severe scalding can easily be the results.

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