Q: What would cause the engine temperature in my 2002 Subaru Impreza to constantly fluctuate.

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Temperature gauge goes from operating temperature (at the first of the two middle lines) up to the second of the two middle lines. It then bounces between the two. I have replaced the thermostat about a year ago, and I replaced the radiator about six months ago. Any ideas about what the problem could be will be helpful. Also, there is no smoke coming from the car, no unusual smells. The only thing that I have found is that occasionally some of the coolant in the reservoir will boil out.

My car has 112000 miles.
My car has a manual transmission.

Hi there. If your temperature continues to do this then you either have a flow issue within the cooling system or you have a small leak in the head gasket. I usually start by doing a block test on the engine to see if there is any signs of compression gases entering the cooling system. If it fails the test then you more than likely need head gaskets. If it passes the test then I would check the flow as the water pump may have an internal failure. If you need some help diagnosing this, consider YourMechanic, as a certified mechanic can come to you to [diagnose why the engine is overheating] https://www.yourmechanic.com/services/car-is-overheating-inspection

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