my temperature gauge was moving up and down today but car wasn't overheating, and the key was really hot when I took it out of the ignition. The ignition was hot too. Where to start to diagnose this?
If it was hot outside your temp. gage will fluctuate as the thermostat opens and closes to allow the cooler coolant into the engine. Long as it is not overheating, I would check your coolant level to see if any needs to be added, when the motor has cooled down for a more accurate fluid level.