I have a gt350 coupe and I know when I am parked with the a/c on it will overheat in an hour, so I need to turn a/c off. But this time while driving the temperature gauge started going down, not overheating. The car is driving fine and produces no sounds out of the ordinary. Then last time engine light came on... Do I need to service my car?
Make sure there are no leaks. A pressure tester can help you do this. Or you can keep running it and monitor usage by noticing if the level drops after multiple uses. But with engine temps varying like they are I would do a pressure test and confirm it isn't a head gasket problem or air getting into the system. If it passes a pressure test, the most likely cause is a faulty thermostat. If it fails the pressure test and there is no external leak, then a compression test is needed to find a head gasket leak. But hopefully you won't have to go that far.