This tip is mainly for cars with a/c.

 

Last weekend was quite hot here and while I had noticed the a/c was having a hard time keeping up, I didn't notice the temp gauge creeping up until I heard a little pinging while pulling away from a stoplight. (I have my timing advanced a bit from spec)

 

When I looked at the gauge it was up to about 2/3rds but quickly dropped down to normal. At that point I wondered if I had a thermostat sticking or the beginning stages of a head gasket leak.

 

I checked the coolant level and checked for bubbles and since all was fine there I just kept an eye on the temp gauge on the way home. It acted up the same way one time pulling away from a stop light, but was fine after that as the sun was setting and outside temps were dropping.

 

The next afternoon on my lunch break I discovered I had no a/c. The compressor was shot - running but not pumping. I quickly figured out then that the compressor was on it's way out the day before and was not building enough high side pressure to trigger the electric fan at an idle. The fan was only coming on either when I accelerated and built up enough pressure, or when the radiator temp switch kicked it in. Thus the fairly wide fluctuation in the gauge.

 

So, if you're running the a/c and it's not cooling well, it may be low on freon or the compressor may be going bad, thus not allowing the fan to stay on like it should. No reason to panic since the temp switch should kick it in, just something to be aware of. Be prepared to get the a/c serviced soon.

Interesting. Thanks for the notice McDave.