Here is my problem. I have 160 deg thermostat, it seems at idling
or just crusing the streets is fine. but when I hit the highway and turn on my air I notice my temp gauge slowly start to climb to 200+deg. When I turn off my air while still going down the highway it slowy declines to about midway and stays there. But it stays right around 160 deg. in rush hour stop and go traffic even with the air on? Any ideas I cant seem to find any leaks anywhere.

 

Do you still have the airdam on the car?

 

Have you tried bleeding the system at all to see if there is a small bubble or something?

 

The first summer mine was doing this, and i had the radiator rodded out, cured it for that year. the next summer it started doing it again, so I bought a new radiator. problem gone for 3 years now.

But check the easy stuff first, air dam, etc. as the others have mentioned. Also, recently mine was acting that way again, and I crawled up under the car, a large paper bag was sucked up to the radiator, blocking about a third of it, that was the easiest fix yet. "hey, I bet if I pull the trash off of my radiator my car will run cooler"

 

I still have the air dam but it seems like its about to come off. Ill try bleeding the system out maybe that will work. I just got a new radiator last year.