Temperature gauge not working properly?

Hi,

If the heater helps cool it, my first suspect is the coolant thermostat. It may not be fully opening. However, first check the coolant level to make sure it is full. Do this when the engine is cold.

If that isn't a concern, then I would replace the thermostat. Additionally, when it is apart for the thermostat, I would flush both the radiator and engine block.

Here is a link that explains in general how one is replaced:

https://www.2carpros.com/articles/replace-thermostat

Here is a link that explains how to drain and flush the cooling system:

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Let me know if you are comfortable doing these things and if you have other questions.

Take care,

Joe