The Automotive Cooling System
Thermostats are located in the water flow housing (usually in the top hose outlet) and are of wax pellet type. The thermostat is used to restrict coolant flow to the radiator until the engine warms up. As the coolant temperature rises the valve opens and allows coolant to circulate through the radiator.
Opening temperatures vary depending on vehicle manufacturer but most open between 82 – 92 Deg C with the exception of late model Fuel Injected cars 89 – 93Deg C . Two stage thermostats (Ford Falcon) are used to provide a direct flow to the radiator when fully open. It also closes off coolant bypass unlike single stage thermostats.
Never remove a thermostat as this can cause coolant to circulate too rapidly reducing its ability to dissipate heat causing overheating. It can also cause over cooling. Over-cooling can cause excessive fuel usage usually shown by black soot on the rear of the car. As an example the Holden Commodore V6 engine has an air bleed system incorporated into the top radiator hose/ thermostat housing to release air pocket.
As the engine is higher than the radiator it is possible that air bubbles may remain trapped causing the coolant to sit on top of the trapped air giving a false impression that the coolant is full. To overcome this use an empty bottle with the bottom cut out to allow the coolant level to be higher than the engine, thus forcing any trapped air out of the bleed hole.