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What are the symptoms of a bad thermostat?
If the thermostat breaks down, the engine might take a very long time to reach the working temperature, or, on the contrary, it will overheat fast. During acceleration, the engine temperature may decrease abruptly, and increase as sharply right after you stop the vehicle. Interior heater becomes less efficient. The temperature of the lower radiator pipe is another indication of a bad thermostat: if it becomes warm right after you start the engine, this means that the valve of the part is stuck open. While if the pipe stays cold after the engine has reached its working temperature, this indicates the valve is stuck closed.
In some cases, a bad thermostat can cause the “Check Engine” light to come up. Diagnostic scanning can reveal the corresponding error code. This doesn’t happen in all cases, though, that is why you still need to consider the symptoms described above.
It happens that the engine won’t start at all if this unit is faulty. For instance, this refers to MINI cars which have thermostats with built-in coolant temperature sensors. If this sensor fails, the engine will start and stall right this instant. Sometimes the ECU blocks the engine start.
How do you fix a stuck thermostat?
If during diagnostic scanning you found an error code indicating a stuck thermostat, replace the component. It is the only way to fix this issue.
Can you drive a car with a broken thermostat?
No, you can’t. The thermostat should be functioning properly, as the operation of the cooling system directly depends on it. If the valve is stuck open, the coolant will be circulating through the large circuit, thus significantly increasing the engine warming-up time. This increases engine wear and load on the lubricating system. If the valve of the thermostat is stuck closed, the coolant does not flow to the radiator and is not cooled, which causes engine overheating.
What problem can occur to an engine if the thermostat is installed upside down?
The component should be installed exactly in the position specified by the vehicle manufacturer. If the part is installed upside down, the valve will operate incorrectly which may lead to coolant boiling, as it will flow inside the smaller circuit only. This may result in engine overheating.
Why is my car overheating with a new thermostat?
It is possible that the new unit wasn’t tested before installation and you got a defective or poor-quality part. The same problem can also be caused by improper installation of the part. If you are sure that the part is in good condition and properly installed, this means the cause of overheating is elsewhere. For instance, you may have a clogged radiator, air locks in the system or a critically low level of coolant. In some cases, the overheating problem occurs even in a properly functioning cooling system. This happens, for example, if the cylinder head gasket is torn, there is a blow-by of exhaust gases or problems with fuel injection, mixture formation or ignition.
Do I have to drain coolant when replacing the thermostat?
Yes, in most cases, you should drain the coolant before installing a new component. If you changed the coolant recently and you want to re-use it, prepare a clean container in advance. Some car owners manage to drain the coolant partially through the thermostat hose. However, in this case, there is a risk of spilling the fluid in the engine bay and damaging the electrical components. That is why it is more convenient and safer to work on a fully emptied cooling system.