95 Grand Marquis, Engine temp goes up with AC on???

This afternoon driving on the highway my engine coolant temp gauge started beeping at me. First time I ever seen the temp in the hi range. I immediately pulled over and popped the hood to check coolant levels. All
were fine! Looked for leaks, nope. Looked at fan to make sure it was spinning, yup. Got back in the car and the temp had gone back to its normal reading. I hadn't shut off the engine while checking these things....Started driving again and the temp indicator started going up again!! This time I got off the highway and pulled into a parking lot. Engine is still running. Still no signs of leakage or anything abnormal. Check the temp gauge ad it's back to normal!!!
As I started driving towards home I decided to shut off the AC. The temp gauge stays in its normal range for the next 50 miles. As soon as I turn on the AC, within a few minutes, the temp goes back up. Shut the AC, it goes down!!
What in the AC cause the engine temp to go up? Car has 167K on it. 4.6L V8
-TheKidd
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a) The AC load requires a few more HP, making the engine work a bit harder. b) More importantly, the A/C condenser sits in front of the radiator, and with the the A/C on, it warms the incoming air. Essentially, the heat that it's removing from the inside of the vehicle is dumped (in addition to the power required to move it) into the incoming air. From the radiator's point of view, when the A/C turns on, it's like taking your car from 70 deg to 95 deg weather.
Your cooling system is probably marginal and unable to cope with the extra heat load. I would start with the thermostat; it's cheap and easy to replace. Next would be looking for a clogged radiator, defective water pump, perhaps a collapsed hose. If replacing the thermostat does not help, it may be worth a trip to a professional to correctly diagnose this.
And by the way, you are using the correct Anti-Freeze mixture, and not plain water, aren't you?
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Thank you for the description on how the AC adds heat to the engine. The system was flushed 2 years ago by my local garage. Guess it should be done again prior to the colder weather...I'm assuming they used the correct mixture of water/AF.
I would have thought that a bad thermostat, hose, water pump, etc. would cause the engine to overheat all the time? I suppose changing the thermostat would be the quick thing to do. I'll try that.
Thanks.
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Happy Traveler opined in

Point of interest... water carries heat off better than a mixture...though it is NOT a good idea, for corrosion purposes and boil-point.
Look for debris in front, lots of bent fins, fan performance, stc
I think there's something else.... if he had it flushed two years ago. (but how do you know it was really flushed.. not just billed?)
But the mixture should be as little AF as possible to protect from freezing as long as it's over 40%... never more than 70%
Also... try Redline Water Wetter.. Pepboys carries it. It works in slow rising overheat situations
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Not to mention freezining point. Perhaps that's why they call it "anti-freeze" instead of 'anti-boil'.

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Jeff, AFAIK.. they dont keep count of posts on NG's. So what was your point?
The subject of the thread was overheat..my point was it wasnt likely due to low glycol to water ratio.
And if you read to the bottom of the post you responded to, see the reference to freezing and minimum mixture?
If you have somethng to add... good. If you have a smart-ass comment, put a smiley on it.
Jeff opined in wrote

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My '95 CV has two radiator fans, the regular engine-driven one and an electric one that runs when the A/C is on. It shouldn't make a difference at highway speeds... but it's worth checking. I'd sure check the hoses, if one is soft, it can collapse at speed and things will heat up quickly. You have some good suggestions here - let us know what you find.
PoD
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