Overheating problem

Danger_Ranger_94 · May 23, 2015

Hello all. I'm new to the forum. I've got a 94 Ranger with the 5speen 2wd. It's basically stock except an 87 mustang pausy rear end chunk. I've had an overheating problem since I've owned the truck. If you sit and idle it will never over heat only when the ac Is on. I thought the radiator was clogged up so I bought a 3 row full aluminum radiator. Bought a new fan clutch and went through two of them cause they stayed locked up (cheap aftermarket parts) so I eliminated the mechanical fan and put an electric 16" hayden cooling fan with a hayden universal fan controller. It's set to come on at 190 degrees and I have a 180 degree thermostat installed. The electric cooling fan and radiator didn't change a thing. Still heats up while sitting still with the ac on. The ac never blows warm either and the pressures stay perfect too. While I'm driving it's fine. It has a recent water pump and I've flushed the cooling system many times and put back in 50/50 mix green coolant. I've been a professional tech for about 3 years in a shop and can't figure this out. If anyone has some insight on what my problem could be it would be much appreciated. Thanks!

RonD · May 23, 2015

Overheating only at idle is almost text book fan clutch issue.
Or shroud issue, rad fans don't work well without a shroud, mechanical or electric.

Check if there is an electric fan on the condenser in front of the rad, and that it is working, it gets quite hot when A/C is on.

Also on my '94 4.0l the heater core is part of the water pump bypass system, there is no heat control valve on the heater hoses, so core getting plugged up will effect cooling system.
My symptom was random spikes in temp, never hot but it would go above 1/2 and then drop back down to "normal"(just below 1/2), uphill, downhill, highway speed or idle, totally random.

Other thing which is hard to check is a lean mix at idle, computer ignores O2 sensors at idle and runs a pre-set richer mix, so there would be no feedback if mix was Lean.
Lean mix burns much hotter, it can melt pistons and valves, a vacuum leak could cause it, or low fuel pressure, even dirty injectors.

And just FYI, thermostat temp rating can never have anything to do with overheating.
Correct engine operating temp range is 200degF-225degF, just below 1/2 to just above 1/2 on Ford gauge.
A 160, 180, 195 thermostat would all be open fully at 200degF, so...............
Using a lower temp t-stat can give you more power, very slight though, it will lower MPG and lower temp means contaminants in the oil burn off slower.

Danger_Ranger_94 · May 26, 2015

Well, today I actually removed the e-fan and put the stock mechanical fan back in with a brand new fan clutch. Also it's a new cooling fan. The shroud is in place. There is no electric fan on the front of condenser. It shouldn't need one cause the cooling system should be engineered to properly cool the engine the way it is. While driving Or idling with ac off its fantastic. Ac on and idling the needle just climbs. I also have a an aftermarket temp gauge. Which reads +- 5 degrees what the ect reads. I will try flushing out the heater core this weekend when I flush the cooling system. I'm almost positive it's gotta be a flow problem. Thanks for the advice!

Overheating problem

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