2003 Ford Focus Heat gauge goes up when air cond. on drivin

Any time you go up a steep climb, there will be postings that tell you to turn off the A/C due to the possibiity it will over heat on you. The only thing I can really recommed is replacing the thermostat. If it is stuck open or partially stuck open, it does not give the the coolant time to stay in the radiator to cool down. So for now replace the thermostat and when you do, if there is a posting recommending you turn off the A/C for a steep climb, do it or you are risking engine damage if you over heat.

I am going to have the thermostat replaced, and see what happens, I will keep you posted. Oh, and the engine is a 2.3 cyl. I clicked on the wrong size. If this doesn't work I was told it would be issue with the radiator, but I will try the thermostat first. Thank you!!!!!!

Yes that will be the frst step. Keep us posted.

I am also having that same problem but my ac has not worked for a long time so I just put the hot air on. But I was wondering a ball park price of what you paid .

I have brought my car in to my friends' repair shop many times since I wrote this. There have been 3 possible reasons the gadge goes up, 1. the thermostat, 2. the alternator, 3. a grounding issue with battery and/or electric. My mechanic put this heat sensor on my engine when the gadge said red, and the engine was at the average hot point temp and should not be in the red, thus he thinking it is an electrical thing. I have been recently driving with the AC on and the gadge goes up and then down and some days not at all and others after 10 miles of driving, CRAZY. So, not sure what to do. The thermostat is a $30. or so part, labor should not be bad but most places may charge you $150. for labor. You also want to make sure your fans turn on when your car is hot. I really am at a loss here. I did change my battery out a few months ago, it was due but I think this is an electric issue for me. My gas gadge was wierd the other day when I had over half a tank, my gadge said it was empty when I started it and said it was full a few hours later. I do remember being in a rain storm last year and my dash board went crazy and stopped, when I had the engine off! So, again, still not sure what to do here, and if I take it to the dealer, my opinion is I may spend a lot of money there.

If you were from around here, I'd say your radiator has mineral deposits growing (forming) on it's interior. (from the water)

The radiator may no longer be capable of cooling the water as it runs thru it, as it did prior to the formations.

Auto parts store "flushes" will not touch it.

The only thing that works is to take 'em to a radiator shop, where it's disassembled, vatted, and the vanes are rodded out

I'm sure some of the new, mostly plastic dealees are disposable, and may not be able to endure the process.

You did say, "Heat Gun"? Maybe you could monitor what's going in the top, and is it cooled much at all, as it leaves the bottom.

On my Jeeps (unrelated) I'm unable to hang onto the top hose very long, but I can hold the bottom one forever, after the radiator has cooled the coolant.

The Medic

Thank you for your feed back. This Focus has a plastic radiator which I replaced and a new cap, and I had a professional radiator flush, so that was actually the first thing I did when this all started.
With your jeep, same thing here.
Wow this is wild.
Thank you.

Maybe your fan is intermittent, like the fan relay's internal contacts are burned.....sometimes it works...sometimes it don't?....It does happen!

Somebody's info is wrong, Autozone only shows a 4 cylinder engine!

Yeah, I throw parts at the problem sometimes, sometimes it works...saves time!....sometimes it don't!

I have jumper wired a test light to a fan motor, ran it back into the cockpit, when the test light comes on, the fan should be on...provided that we know the fan motor does work!

This thing has constantly operated 8? years?.....If I ain't your fix, you now have a spare relay!

The Medic