To keep the interior of the vehicle warm a small radiator called the heater core is used. To operate this small radiator inside the vehicle a system of valves and/or baffles is usually incorporated into it.
Remember that if you heat the inside of a vehicle, it will also help to keep the engine cool. It is for this exact reason that you are always advised by a mechanic, that if the engine of your vehicle is overheating, you are to turn on the heating inside the vehicle.
When the coolant goes through the system, it flows through a thermostat, which controls the rate of flow back to the radiator. This is where it is then cooled again by convection with the air. This process will cool the entire engine. A lot, if not most heater cores will bypass the engine’s main thermostat and heat in the passenger compartment will not either a working thermostat or even an engine temperature that sufficient to open the thermostat.
So, by the time the superheated engine coolant has made its way through all of the chambers of the radiator, it should then be cool enough to make it’s a return trip through the engine block. But, if the coolant flow is reduced by a blockage or any loss of fluid, the engine block will not be cooled down and this will then cause the engine coolant to boil over. Therefore, it very important to maintain a full coolant level at all times, especially during the hot weather or when doing long drives.
Some engines have an additional oil cooler, which is a separate small radiator that is used to cool the motor oil (used to for lubrication by various kinds of motors, especially in internal combustion engines).
Turbo charged engines may also contain an intercooler, which is used to improve the volumetric efficiency and increase the amount of charge in the engine, thereby increasing the power.