What are the symptoms of a bad engine thermostat?

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asked Sep 30, 2020 in Repairs/Maintenance by 1232newt (1,010 points)
What are the symptoms of a bad engine thermostat?

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answered Sep 30, 2020 by Larry S (42,350 points)
The symptoms of a bad engine thermostat are engine overheating, engine not heating up properly, temperature gauge jumping from high to low temperatures.

A bad thermostat can either be stuck closed or stuck open and so the symptoms of the bad thermostat can vary.

If the thermostat is stuck closed then the engine will overheat because the coolant will not be able to pass through the engine too the radiator.

If your temperature gauge continues to climb then you could have a bad thermostat or something else could also be going on.

If the top radiator hose does not build pressure but the bottom one does and your engine is overheating then you likely have a stuck thermostat.

If your heater is blowing cool air or lukewarm air then it could also be a bad stuck open thermostat.

Also check for coolant leaks around the thermostat housing as that is also sometimes an indicator of an engine thermostat being bad.

You can drive a car with a bad thermostat as long as the thermostat is only staying open and not stuck closed.

If the bad thermostat in your engine is stuck open and not closing then it's okay to drive your vehicle with the bad thermostat being stuck open.

However the engine will not be able to get warmed up properly and the heater will usually not work with a bad thermostat.

If your engines thermostat is stuck closed then no you cannot drive the car with the stuck closed thermostat because the engine would overheat.

The coolant needs to flow through the thermostat and into the engine and back to cool the engine.

The engines thermostat works by responding to the changes in the temperature of the engine coolant and when the engine and coolant is cold the thermostat is in the closed position.

The thermostat then stays closed until the engine warms up the coolant so you may see your temperature gauge go up when first starting the vehicle which is normal.

If the thermostat is good and opens then the temperature gauge should go back down and if it does not then your thermostat could be stuck closed.

The thermostat opens once the coolant is hot enough to allow the coolant to flow through the radiator.

A new vehicles thermostat is only about $5.00 or $10.00 and they are pretty easy to replace but you need to drain some of the coolant and remove the thermostat housing and replace it with a new gasket.

A shop could replace the thermostat for around $50.00 to $100.00 in parts and labor depending on how hard it is to get to the thermostat.

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