Last night I finished putting in a replacement HID bulb and drove my car home which is a half hour drive. I got home left the car running while I went in for a minute. I came back out and got in my car and noticed the temp gauge was almost maxed out. Having this happen once before I popped the hood with the car running and slowly loosened the coolant cap to let the excess air out. It took about 10 mins to get all the air out without overflowing the tank.

After that the temp started to come down a little so i got in and drove it for a short drive. The temp gauge dropped to about halfway between the C and the normal operating temperature. It only comes up when sitting still. Any Ideas?

I am going to replace the thermostat again. Luckily when I put that one in I got a failsafe that locks open if it overheats.

 

Definitely sounds like a Thermostat or temp sensor. Sounds like your thermostat was stuck closed (overheating) and open (running cool). Hopefully that works, easy and cheap fix

 

so another quick question if someone has a quick answer it would be great...car is going in shortly.

yesterday it through a cel. Had it scanned came back with 1296. cooling system malfunction. could a thermostat stuck open for a few days cause this? Also noticed that the coolant in the tank is extremely low until i run it then it comes up to normal.

 

So I finally fixed it...Luckily I had put a failsafe thermostat in it before because it was the fan fuse on the battery that was junk. It was weird because it didn't actually blow. it looks like it got really hot and corroded. replaced and the fans came back online.