Author Topic: AC causing engine overheat while in 4L and in high heat and low speeds.  (Read 1946 times)


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I was told to come here to post up for some. I haven't used a forum system in a couple years and have just been sticking to Facebook groups, so bare with me. 2004 Montero Sport xls

Here's what I'm talking about-

1:doesn't overheat in 110+degree heat when AC is on and driving around moab/Phoenix/streets/highways in AWD.
2:doesn't overheat when AC is on and in park while off-road in those high temps while in AWD.
3:doesn't overheat when AC is on and wheeling in Midwest 90-100 degree heat in 4H/4L.
4:doesn't overheat when AC is on and in AWD and cruising white Rim or dirt roads around Moab 30-40 mph.
5:doesn't overheat with AC on when in 4H while cruising washboard roads around Moab and chicken corners at 25-35 mph.
6:doesn't overheat with AC on in 4L while crawling snail speed in summer heat of Kansas, Missouri, Illinois, or Washington.
7:doesn't overheat while I n 4H or 4L if the AC is not on at all.

1:overheated with AC on when in Park with 4L engaged while on Hells Revenge.
2:overheats when AC on and in 4H or 4L going snail speed on hells revenge/white Rim, and other trails.
3:pretty much just overheats when in deserts at 110+ degrees(maybe even a little over 105) while in 4H or 4L(it has to be well over 120 degrees to overheat with AC on and in just AWD).

*if the truck overheats because I forget to not run the AC(because it's always hot as balls when crawling rocks through the desert at 2 mph), I just turn on the max defrost on high heat for 10 minutes and go scout the trail ahead. By 10 minutes, the truck is back to normal operating temperature.

The solution would be?

1: replace mechanic oem fan with electric dual ones or Volvo single? Someone also said something about Ford.
2: add trans cooler to open location next to oem electric condenser push fan.
3: swap out Zerex Asian coolant and for something better.
4: instal snorkel to get cooler air intake.
5: add vents in hood to help release heat from engine bay.
6: add another electric fan to open spot next to factory oem fan on condenser.
7: make it so oem condenser push fan is constantly on at all times.
8: clean out air condenser again with air hose.
9: buy new condenser for $200-$300.
10: buy 2nd or 3rd gen Montero trans cooler and install to factory location in front of condenser or buy aftermarket one.
11: splice another electric push fan for over trans cooler.
12: remove oem mechanical fan for electric fan or fans.
13: have the engine fan always on or have a switch inside for it.
14: have dual electric pulled fans and have the one on the passenger side of radiator have an on/off switch but the driver side one always on.

So it seems like 4H and 4L have something to do with overheating when the AC is on. It won't overheat if the AC stays off though. If I do overheat, turning on the heater cools it down quickly.


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Your truck shoud have a trans cooler already, you probably don't have an engine oil cooler as most sports if any at all, come with this. I will almost guarentee you, the transmission has very little to do with engine overheating. Unless your trans temp light illuminates while engine temp gauge climbs. When's the last time you rodded or replaced radiator? Fan clutch? Water pump?

You issue lies more in the engines cooling system. Electric Fans are really good for cooling, and may solve your problem. But I will say, even with a proper cooling motor and wheeling at slow speeds when it's over 100 degrees, may just want to soak up that summer heat. Well maintained vehicles could still struggle with this.

You could always upgrade to electric fans, 3 row or aluminum radiator, add a second pusher fan behind the grill to assist the current condenser fan, wire a switch to consenser fan to help without ac on. This could all really just be covering up an internal engine failure or improper cooling of your current system.

Take baby steps first, replace your radiator cap and thermostat, replace coolant/flush. Replace or have your radiator serviced. Fan shroud, fan clutch, the fan itself maybe?

By the way, the ford fan is the Taurus fan, that and the Volvo fans are beast mode fans, really awesome