Car overheats, but cools when you turn the AC ON. Explain.

MyLittlePony · May 18, 2024

Ok, so my car has been over heating, and most everything on the car is new, or very low miles. When the AC is off, car will get about 230 degrees before I start freaking out, but I don’t want it to peg. If it pegs before I can pull over and turn the car off, then the car will not crank after I do turn it off. I am assuming that’s computer related. Wait half an hour with the hood open, and it will start again.

So car starts overheating, naturally your first impulse is to turn on the heater, right? The heater seems to only press the pause button. The temperature remains whatever it is at, whenever you’ve turned it on. 230, stays 230. Pegged, it stays pegged.

The number one thing I THOUGHT you should never do in this situation is to turn on the AC. That’s more load on the engine, it will make things worse. Well, I noticed that when the car is around that 230, if I turn on the AC, it will drop to 190 degrees, and stay there. This has been tested and proven several times, but I am always nervous about doing it. Ok so what’s going on? Any ideas?

shovel · May 18, 2024

Low speed fan not turning on, ccrm failed or engine coolant temp sensor failed. Buy or download a FSM and test each component.

lwarrior1016 · May 18, 2024

Bingo. Fan is only working when the ac is on.

cobrajeff96 · May 18, 2024

Could just be a bad coolant temp sensor. If the high speed fan doesn't even come on when the temp gets really high, I'd start there at the coolant temp sensor. Take a length of wire and ground out one of the pins. The fan should come on.

If you need a replacement temp switch, it might be Motorcraft SW5110 though I can't be sure for your exact car.

Musturd · May 19, 2024

The high speed fan kicks on with the ac so it’s cooling the car . Good chance the low speed isn’t working or the fans not kicking on at all with out the ac . Ccrm is most likely the culprit . Also could check the coolant sensor but it seems like it’s working .

Wood's 5.0 · May 20, 2024

Agree with all of the above.

MyLittlePony · May 20, 2024

CCRM has been replaced numerous times. Temperature sensor, I’m not sure. It’s grey like the original motorcraft. Could be 30 yo, 20, 10, could be new.

The other day I drove around for a quick jaunt, then had my husband observe the fan. He said it seemed to spin faster when I turn the AC on. When I turn the AC back off, it slowed down. Car has a variable speed controller attached to it. Just another arching added to help the car stay cool. There is an adjuster screw, so I will have to see later if my adjustment helped.

Flex-a-lite 31165 Flex-A-Lite Variable Speed Controllers | Summit Racing

Free Shipping - Flex-A-Lite Variable Speed Controllers with qualifying orders of $109. Shop Fan Switches at Summit Racing.

www.summitracing.com

lwarrior1016 · May 20, 2024

If you’re using that fan controller, you aren’t using the ccrm for fan function, and probably not even the temp sensor.

Id start looking at that controller for fault, or even a fan going bad. Do you still use the stock fan?

cobrajeff96 · May 20, 2024

The plot has thickened.

MyLittlePony · May 23, 2024

lwarrior1016 said:
If you’re using that fan controller, you aren’t using the ccrm for fan function, and probably not even the temp sensor.

Id start looking at that controller for fault, or even a fan going bad. Do you still use the stock fan?

Car has an upgraded Taurus e-fan, cooling an aftermarket aluminum radiator, radiator number 3ish. It’s also on its 3rd CCRM. Hardly anything on this car is original anymore. The e-fan and variable speed controller was the latest attempt at controlling a lifelong cooling issue. And yes, it’s been flushed numerous times. It’s not even the original engine, though when the original overheated, new radiator hoses solved it for a few years. Of course, it was only like a 10yo car then. The hoses on it now are also new, from this year at least.

ttocs · May 23, 2024

Doesn't the stock fan have 3 wires going to it, low speed, high speed and ground? is the fan controller made to control a 3 wire fan or a standard 2 wire? I bet it is made to control only 2 wire fans(most are made this way) and it is only hooked up to the low speed. Turning on the AC possibly makes the high speed get turned on bypassing the controller.