auto fan / thermostat.
the piston of the engine is never a true cylindrical shape.
the head of the piston / ring area diameter is slightly less then the rest of the piston.
as the piston heats up, the diameter increases, creating proper seal and compression.
this temperature is maintained, by the thermostat valve, and the automatic fan. normally between 80 - 90 degree of coolant temperature.
when engine starts up, the thermostat valve is closed. the coolant circulates within the engine block only. as its small quantity of coolant, it reaches temperature quickly.
when temperature is reached thermostat valve starts opening, and allows coolant from the radiator circuit to flow through the engine, since the external coolant circuit will be cold, it will take some time to reach the operating temperature. until then the thermostat valve will open and close maintaining the temperature.
when the entire cooling circuit reaches operating temperature, and then exceeds it, then the auto fan will start and cool the coolant flowing through the radiator, it will shut off again, when the coolant reaches operating temperature.
the radiator, thermostat valve, thermostat switch (auto fan) all work in combination to ensure engine operates at optimum temperature.
what happens when engine runs cold all the time:
the piston head, never heats up or expands properly. this means that oil from cylinder wall makes it way into combustion chamber. and combustion gases make their way past the piston rings into the oil chamber. the cylinder oil lubrication film is also washed out.
this leads to poor fuel economy, engine oil consumption, faster engine oil degradation, excessive piston ring wear, and cylinder bore wear.
ultimately engine will start smoking first and then consuming oil rapidly over a period of time.
