OK here is my situation. I have a 91 NA 130K on the clock. I have owned it since she was at 18K and the temp gauge never ever has risen past the dead level point. Last week I was cruising down the highway at 80 with the AC on and I was not sure if I was seeing things but the guage looked like it was slightly above the mid point. Kept my eye on it and she kept rising. I started to freak and turned off the AC looking for the next possible place to exit and check things under the hood, but before I could the gauge dropped back to dead center like usual. It has done the same thing a few more times to me. Has this happened to anyone? Do I have a problem?

Any insight is much appreciated.

Thanks

 

AC puts stress on the cooling system . If you can, test the fan on the front of the AC condensor to see if comes on. The easiest way to test the fan is to pull the single wire Coolant sensor that sits on top of the thermostat cover. Disconnecting this wire is supposed to tell the ECU the temp is over 210 degrees, or the AC is on, triggering the Fan. (Car must be in on/run position for this to work.

 

That fan on the condensor is spinning. Weird thing is that driving around town with AC on does not cause the guage to move, only highway travel when RPM's are constantly at 3,000 or higher.

 

^hmm that is weird..... driving around town is fine but highway driving raises your temps...

i know this will sound stupid but you might need to add coolant

 

As long as you're not loosing any water, check radiator hoses to be certain they do not collapse, and that they stay open, esp. the lower hose. Also if the radiator is slightly clogged, the water temp will tend to run higher at highway speeds, rather than in city driving. Make certain thermostat is opened all the way, or if it's been a while, change the thermostat and check the cap pressure.