My thermostat needle goes to hot, the temperature light comes on, but once I am driving on the freeway the needle goes back down. The car never overheats. Is it just a thermostat needing replaced?
My car has 148000 miles.
My car has an automatic transmission.
This can be caused by a number of things such as low coolant levels, a faulty thermostat, or a failing coolant fan switch. As you may know the coolant fan switch helps to maintain the proper coolant temperature by turning on and off at specific temperature thresholds.
When this switch is not working properly, this can cause the fans to come on intermittently, all the time or sometimes not at all. When this happens you will notice a temperature spike and drop occasionally as the fan comes on and off. This may also explain why the temperature drops once you are on the freeway as the wind helps to cool the engine down.
I would suggest having a certified expert, like one from YourMechanic, come to your home to diagnose your cooling system and help you fix it as necessary.