I have a 2003 ford focus with 85,000 miles it. I've had it for two years and it's been serviced regularly.
On Easter Sunday I went to pick up my friend. While I was waiting for her outside I noticed that my thermostat was raising and it rose to about 3/4 before I shut off the A/C and turned on the heat. Once I started driving again the temperature went back down to normal.
I took the car to my friend, who is a mechanic, a week later and he was unable to find anything wrong with it. He thought it was possibly the thermostat but couldn't replicate the problem. He said that everything looks good, nothing is leaking, the fans are working, and to keep an eye on it.
I haven't noticed any problems with it all week until today. I went to pick my roommate up from the airport and I noticed that when I stopped at a red light the temperature rose slightly. When I pulled up to the house I let it idle for a minute and sure enough the temperature rose all the way to 3/4. Then I decided to drive it around the block, and the temperature went back down to 1/2. As soon as a let it idle again it started rising.
It doesn't do this all the time. It probably won't do it tomorrow, but I'd like to get this fixed ASAP! Is the thermostat going out? Or?