Overheating in town and I am flummoxed

[ck1938]

My 91 Explorer XLT almost always gets hot when driving in town. I can drive hours on the highway non-stop or let it idle for an hour and it won't heat up. But if I spend 5 minutes going from stop light to stop light the temperature indicator starts getting above the L in Normal and the air conditioning gets hot. I've done a few things:

1. Replaced the thermostat - no luck

2. Tampered with the fan clutch so it is always going - no luck

3. Removed the thermostat - no luck

4. Flushed the cooling system - no luck, the water just boiled over and overflowed the reservoir

I just saw a post about checking the lower hose so I will try switching that out next. Any other ideas? The radiator is new, or so the previous owner told me. Water pump maybe? Any advice would be appreciated

 

[Darrman]

If I had to guess I would say the fan clutch, your problems sound just like mine before I replaced the original fan clutch. The water pump will work until the bearings fail and it seizes up. You will know a long time before it happens, it will squeal like crazy. A dirty radiator can cause overheat, but if you just flushed it, then its probably the clutch.

 

[shamaal]

No offence intended, why do you think it's overheating? What are the sypmtoms?

The reason I ask, just recently after a lengthy discussion and troubleshooting thread, the problem turned out to be a bum gauge/sensor. This was verified with a test drive showing the actual temperature to be spot on although the gauge said hot.

Is it overheating from lack of water? A search for the leak would ensue, if not apparent the head gasket becomes suspect.

If the coolant is full a simple fan clutch test is to spin the fan by hand when cold, then spin it by hand after warming up, there should be an appreciable difference in resistance. Cracks in the fan itself has also been a culprit. The air conditioning getting hot points to inadequate heat removal. I don't believe the 91s have an algorithm to shut off the A/C compressor when overheating.

#4 may be a bum radiator cap opening prematurely or performing as designed.

Your symptoms sound like thermostat, removal and the same symptoms removed that as a possibility. I'm not sure if flushing the radiator establishes that it's good. My daughter had her radiator replaced under an extended warranty that allows used parts.

There have been stories from other vehicles about bad water pumps with badly worn impellers or even broken shafts, but it's low in likelihood.

It has been said that the lower hose may collapse when worn and choke off flow, most certainly sounds plausible.

Let us know what the symptoms are.

 

[ck1938]

No offence intended, why do you think it's overheating? What are the sypmtoms?

Let us know what the symptoms are.

The engine gets extremely hot, the temperature gauge goes past normal and towards the red, the cool air from the air conditioner turns warm. If I fill anything to the cold line in the reservoir it boils over. Basically everything you'd expect to see when a car overheats.

 

[ck1938]

If I had to guess I would say the fan clutch, your problems sound just like mine before I replaced the original fan clutch. The water pump will work until the bearings fail and it seizes up. You will know a long time before it happens, it will squeal like crazy. A dirty radiator can cause overheat, but if you just flushed it, then its probably the clutch.

I saw another thread that showed how to get the fan clutch to engage all the time. I did that test and it overheated with the fan clutch engaged full time.

 

[JDraper]

Time to run a leakdown test on the system. This will tell you if you've got a problem like a leaking head gasket. What a leakdown test does is pressurize the cooling system, and then looks for a degradation in pressure over time.

 

[vrytired]

I saw another thread that showed how to get the fan clutch to engage all the time. I did that test and it overheated with the fan clutch engaged full time.

you drilled a hole and put a bolt thru it? if its lost all its fluid i don't see screwing with the little thing the coil turns having much effect.

 

[ck1938]

you drilled a hole and put a bolt thru it? if its lost all its fluid i don't see screwing with the little thing the coil turns having much effect.

This is the fan clutch test I got from Mr. Shorty in another thread:

The only time I've had success testing my fan clutch by hand was when it wouldn't spin freely at all. When I found that the fan clutch on my '92 wasn't spinning fast enough, I diagnosed it using a trick I got from the Motor service manual.
1) Remove the fan clutch.
2) On the front of the fan clutch is a coiled "spring." This coil is what senses temperature changes and causes the fan clutch to tigten up.
3) The outside end of this coil is stuck in a notch to hold it in place. If you pull the end of the coil out of the notch and rotate the coil 1/4 turn CCW, you will cause the fan clutch to always spin at it's top RPM.
4) Replace the fan clutch and drive the vehicle. If you've cured any overheating problem, you can deduce that the fan clutch was the problem and replace it. If this doesn't resolve an overheating problem, then put the end of the coil back in it's notch to restore normal thermostatic action of the fan clutch and look elsewhere.

 

[JDraper]

If the spring is broken, that won't work at all. Don't discount the fan clutch still being the culprit. That would give you the problem you're seeing.

 

[MrShorty]

Are you certain there is good water flow through the radiator? Might be time to take the radiator to radiator shop and have them do a flow check on it.

Is there adequate air flow through the radiator (and condensor and transmission cooler)? Might be time to peak down in between the radiator and the condenser and make sure it's clean in there, then squirt some compressed air/water through the radiator and condenser fins to make sure air can get through there.

 

[Jason94sport]

If you already removed the fan clutch to do this "mod" you should have just have repaced it. I'd say replace it & the fan & see what happens.

 

[savagefan]

You fill the res to the cold line and it boils out? Does the coolant smell funny/ kinda like exhaust gases?

 

[ron2]

Your initial post said that the overheating occurred in stop and go traffic. idle was not a problem and highway cruise was ok. It seems to be when there is dynamic, non-steady state conditions of engine rpm and load change through the gears. Steady state at idle is acheived after initial warm-up. Question: will the overheating resolve if you cease stop and go driving and sit at an idle? Likewise, at highway speeds, steady state is acheived in top gear, level road, traffic flowing smoothly with the engine rpm at about 2000-2500 rpm. Does leaving the streets and entering the highway bring down the temperature? How does the temperature react to climbing hills or mountain grades? How did changing the lower radiator hose affect the temperature? Sometimes a wire coil spring, just smaller than the internal diameter of the hose is used to prevent pump suction collapse of the lower hose. I've not seen this used in the explorer since the hose is formed with bulit in bends that tend to stiffen the hose enough to prevent collapse but you never can say what a hose might do with relatively sudden suction changes of changing rpm. hope these questions and comments help to sort through the possible problems and bring a remedy.

 

[91n93explorer]

i had every problem in the book with my cooling system, I replaced the core, hoses, water pump, therm, belt...
Ended up ditching the fan and getting an electronic fan and radiator. It did the trick. also added a crapload of HP.

Check Ur Radiator, They tend to get clogged and screwed up.

 

[ma96782]

Explorer Overheating:


http://www.explorerforum.com/forums/showthread.php?t=162848


My STOCK answer on over heating problems: (beside changing a radiator or water pump)

T-stats can be checked w/ a thermometer and a pot of hot water………or just replace them……….they aren’t that expensive.

If you got the tools or access to the kit........pressure check the system.

While running and with the engine off, make a visual check of the hoses for a hole, check for leaks at the connections. If it passed the pressure test, you should be OK. But, still check for a, "too soft" hose, which may collapse.
_____________________________________

Replace radiator cap........IF, you can't remember when it was last done........or if it's been more than a couple years since it was last changed. If it passed the pressure test, you should be OK.
_____________________________________

Fan Clutch...............when cold (engine off) try spinning the fan....it should spin freely or with very little resistance. If it won't spin.....replace.

When hot (engine off) try spinning the fan........in some cases it will feel like it's, "locked up," or it will be like there is syrup/glue holding it back. Tougher to spin, than when it was cold. If so, It's OK. If, it spins like a top.....replace.
_____________________________________

The below elec. tests are the, "cheap test methods"........there are more sophisticated tests with values, that can be run.

Test for the dash thermo gauge................disconnect the wire from the temp sender unit.........KOEO...........ground that wire.........it will peg the gauge on the hot side............disconnect from ground and it will return.

Sender unit.........if you suspect it..........replace, replacement is cheap.

Aloha, Mark

PS............don't forget the anti-freeze and mix it right.

 

[ck1938]

Thanks everyone. I decided to listen to Jason and got a new fan clutch rather than depending on the manual test. It's been 3 days and no overheating. If all goes well by the weekend I'll be putting the thermostat back in and calling it done. I appreciate all your help.

 

[shamaal]

Super, glad to hear it wasn't bad Karma, global warming or George Bush.

If you could, I believe you tried the spring trick and also the hot and cold hand spinning test. Am I correct in that these didn't catch this particular problem, perhaps the results were ambiguous?

It helps in future advice knowing the tests may not be 100% effective.

Thanks!