Overheating when using A/C


Junior Member
I have a 1988 Ford F150 that seems to be in pretty good shape all around. But I recently had the A/C Fixed. And they actually upgraded the entire system to the new kind of freon. And before I retrofited it, the old A/C wasn't working.
So now that it's up and working I have been using it almost every day. And it seems to work without any problems except on the really hot days. On those days, the engine begins to overheat. It doesn't get into the red zone but when I park it I can see coolant leaking out (from the overflow, there are no leaks in the radiator) onto the ground.

So what do I need to do? A friend of mine suggested I may need a different thermostat. Would that really fix this?

Any suggestions would be greatly appreciated.


Junior Member
Yeah, a thermostat is your best bet. It likely has a 195F in it and it may be malfunctioning. I would flush the cooling system thoroughly, when refilling use about a gallon of coolant and the rest water. Install at most a 180F thermostat. If the temp still seems high, you can go to a 160F.


Junior Member
You can run 50/50 if your cooling system is right. Less coolant will reduce temps though. Water has twice the heat transfer capability of a 50/50 mix.


PlowSite.com Addict
Central CT
1. Check to be sure the radiator cap is the correct pressure (s/b 15-17 lbs) and that it is functioning properly.

2. Make sure the overflow bottle is not overfilled. Also be sure there are no leaks in the tube from the radiator neck to the overflow bottle.

3. Any failure in the above two items, and no matter what t-stat you use wont make a bit of difference. I suspect the cap is the guilty culprit.

The r-134a refrigerant is not as efficient as the r-12 so when changing over a bigger condenser is typically used, more heat thrown to the radiator. usually not a problem but when a component of the cooling system isnt working right things go bad.

BTW in the snow belt anything but a 50/50 mix is asking for trouble come November.


Junior Member
Thanks for the tips.

FYI: We're not in the snow belt. We get maybe 1 inch every 2 or 3 winters. But I agree. I typically run a 50/50 mix.


Senior Member
ford overheating

yes you should check your thermostat. I take mine and put in a bowl of water in the microwave and stick the probe into the water. Set the temp to 200 degrees and see if it starts to open at 170-180 degrees. That will tell you if it opens, and how far.

Also, check your fan clutch. Run the engine so that it is warm,warm, WARM. Your temp Gauge should be in the mid range then shut it off. Grab the fan and see if it spins free, or is locked up. With a warm engine the fan should be locked up so that it pulls maximum air through. If it does not lock up, and the truck does not sound like an old u-haul f350 as it winds up with the 330 engine, then you know that you are not pulling enough air through the radiator. In fact, it could be the cause of your evaporator core failing the first time, as the internal A/C system pressure will rise with temperature.

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