The thermostat is responsible for opening the large cooling system. If you discover that the engine temperature is too high, you should check the temperature of the radiator. It the radiator is cold, it means that the thermostat has failed to open the large cooling system. If, however, the engine takes a long time to warm up, it means that the large system opens too fast. In both cases, the cooling system malfunction is caused by a faulty thermostat.
How does the cooling system work?
The cooling system is comprised of two systems referred to as the small and big circuit, respectively. Until the engine reaches its working temperature, the coolant circulates within the small circuit only, i.e. in the engine block and the heater, bypassing the radiator. After the engine reaches its working temperature, the coolant begins to circulate also in the radiator in order to prevent the engine from overheating.
What is the role of the thermostat?
The thermostat controls the flow of the coolant, switching it between the big and the small circuit. If it breaks down, the cooling system stops working properly. If the thermostat gets stuck in the open position, the engine will take a long time to achieve its working temperature and will be underheated. If the thermostat gets stuck in the closed position, the engine will overheat, even if the radiator fan continuous to work. A defective thermostat should be replaced as soon as possible to avoid engine damage. The thermostat is located in a housing attached to the water pump or inside the engine head.
How is the thermostat changed?
Changing the thermostat requires opening the cooling system, so the coolant must be removed beforehand. Then the thermostat housing mounting screws are removed and the damaged thermostat is replaced with a new unit. It is also necessary to fit in a new thermostat housing seal. Next, the housing is fitted back into place and an appropriate amount of the coolant is poured into the expansion tank. The engine is then turned on and heated up to check if the thermostat operates properly.
What to keep in mind
Each repair of the cooling system is an opportunity to check its general condition, ensure that there are no leaks, and check if the coolant concentration is sufficient to ensure resistance to freezing and boiling within a specified temperature range.