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Old 02-22-2010, 11:40 AM
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1999 4.0 cherokee OVERHEATING.. help!

Hello all,

I have a 99 4.0 that overheated on me during a long roadtrip. By the time I got to a service station, I had to dump 2 qts of oil in and fill the radiator. Now that I am home and all fluids are full, its still overheating and I dont know why. Here are the 'stats/clues':

1. All fluids are full.
2. There is NO smoke coming from exhaust pipe.
3. There are NO weird noises coming from engine.
4. There is no water in the oil.
5. Fans and serpentine belt are intact and operating.
6. For the first 10 minutes after starting car, it sounds, smells and runs normally. After 10 minutes, it smells hot, runs rough and wants to stall while in gear at a standstill. Obviously in "overheat mode".
7. Temp guage is at 0 when car is started, goes up to and stays at about 215 after 10 minutes- even when it smells alot hotter than 215. When overheating first occurred, temp guage was actually pegged in the 'red zone'.
8. Oil pressure gauge indicates 80. Not sure if thats accurate either though. It does go to 0 when car is turned off, but when key is "on" and car is NOT running, gauge reads 80.. hmmm...
9. When car overheated, I tried turning my heater on to circulate more water, but heater now blows cold only (worked fine prior to this). Even now that radiator is full, heat will not blow hot- no matter what setting I use.

Im guessing either water pump or oil pump failure.. leaning towards water pump since heater wont work??? Is there a way to test both pumps to see if they are working properly? Or is there something else that could be wrong?

Please help, this is my only car!!!!!

Thanks,

Mike
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Old 02-22-2010, 11:44 AM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

if hot water doesnt circulate, i would say thermostat.
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Old 02-22-2010, 11:50 AM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

OMG... DUH! Can you say, "I cant see the trees through the forest?" I'll try replacing that and see what happens.

Do u know where the temp sending unit is located? I would think the guage would show alot higher since the car is obviously overheating- unless the temp sending unit is in the radiator?

Thanks again,

Mike
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Old 02-22-2010, 11:53 AM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

idk where the sender is.........
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Old 02-22-2010, 12:05 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

I would wait until the engine is cool, then check the coolant level in the radiator. I had overheating problems in my 92 XJ and the overflow was always full. I just happened to look in the radiator one time and it was quite low. I also had a small leak in the vacuum switch that goes to the heater core. I guess it was enough to not let pressure get high enough to open the valve on the radiator cap. I replaced the vacuum switch, filled it at the radiator and no more problems.

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Old 02-22-2010, 01:35 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

I'd also check your hoses to your radiator and heater core to see if they (4 hoses, 2 for each) are hot. They may be plugged and require a flush or you may have a air pocket stuck in there. Is your coolant rusty at all?

Is your fan shroud still intact?
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Old 02-22-2010, 01:39 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

Ok, so I replaced the thermostat and although the temp gauge still goes to 210-ish and stays there, it seems as though it is not overheating anymore after a 20min idle test. It does not 'smell hot' either, and the heater once again blows hot air, so it seems that water is circulating now! Probably cooked the sending unit, which is screwed right into the thermostat housing, but thats an easy enough fix.

Of course the 100% test will be later this evening when I can drive around (close to home!) for an hour or so....

Thanks for all of your help guys. This appears to have been a classic example of 'start with the simplest forms of troubleshooting before jumping right into a full motor swap!"

Regards,

mike
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Old 02-23-2010, 12:55 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

Just below 210 is where mine always stays. That is not overheating. It has a 195 thermostat. Sounds like that may have fixed your problem.
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Old 03-19-2010, 01:52 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

Also, just as a good measure you might want to completely flush or reverse flush (whatever) your radiator fluid. You might have got a blockage somewhere witch made the coolant sit and not circulate. Where the radiator hoses blown up like balloons when it overheated?
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Old 03-19-2010, 01:56 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

I was going to say definitely sounds like thermostat.. I don't know what it is with those things; I had the one on my wrangler replaced three times when I had it, and one time it still overheated and ended up blowing a hole in the radiator hose (NOT a pretty sight)...
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Old 03-19-2010, 03:35 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

the reasing your oil pressure is at 80 is becasue the sender is broken. it the plugin by your oil filter. and the temp is normal i put in a 180 t stat and it ran around 190-200.
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Old 07-12-2012, 05:00 PM
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Re: 1999 4.0 cherokee OVERHEATING.. help!

Quote:
Originally Posted by Denny boy View Post
the reasing your oil pressure is at 80 is becasue the sender is broken. it the plugin by your oil filter. and the temp is normal i put in a 180 t stat and it ran around 190-200.
Although, it's been a long time ago..I remember removing my 210 T-Stat from my old '84 Cutlass (305 ) and replacing it with a lower temp TStat.
About 2 weeks later..I kept noticing a faint Mildew-ed, rotten/musky smell both in the car and under the hood.
Mechanic told me, the water wasn't getting hot enough, and I needed to bump back-up to my OE TStat.
I've never forgotten that.
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