Hi, I noticed that my car's thermostat will sometimes slowly creep all the way up, then back to the normal operating temperature while I'm driving for about 20 minutes and it'll keep fluctuating until I turn off the car. There aren't any physical signs of overheating like steam, or weird smells from the engine and when I pop the hood the car doesn't feel any hotter than normal. The reserve tank is also still full. Is this a case of a faulty sensor or should I get something fixed or replaced?
My car has an automatic transmission.
The sensor, gauge and wiring should be repaired if there is a reporting fault. The problem is if you leave it as is, you might not get adequate notice were actual overheating to occur at a future point. Overheating of car engines is very damaging, and thus very costly to repair, hence the advice to get this repaired. To resolve this, you can request a temperature gauge diagnostic/repair and the responding certified mechanic will identify the fault in the circuit and get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.