a few weeks ago i noticed my temp guage on a 2002 cadillac deville was fluctuating between reg.(4 out of 8 levels) all the way to 6-7 levels... i have no leaks, no smells of coolant, and ac works just fine. the issue is very spiratic and at a shop i was told it looks like the issue may be caused by a bad thermostat... had the car tested and was told it was the water pump by a mechanic but took to a gm dealer and he's pretty sure it's the thermostat and not the water pump because i have absolutely 0 leaks... is there any further tested that can be done by myself to ensure this is the thermostat and not a costly repair.