HELP IF YOU CAN...OVERHEATING..I THINK

[BOLO1994]

Here are the details:

Vehicle: 1999 xj, 4.0l., 4wd

Problem: temp guage jumps to redline

Driving conditions at onset: I live in AZ and the jeep runs between 210 and 220 degrees with AC on. The jeep temp guage jumps from just over the first mark past 210 to redline. The "check guage" light illuminates and alarm sounds. I shut off the AC and in about 1 minute the temp guage drops back down to just below the 220 degree line. The drop is rapid. Sometime I use turn the heater on to assist in cooling, but it doesn't necessarily fix the overheating issue any faster.

Corrective actions already taken: Replace thermostat twice, replaced temp sending unit twice, replaced water pump, replaced both top and bottom radiator hoses (yes the bottom hose has spring inside), flushed system multiple times both manually and reverse flush by machine, burped system everytime I changed something, and changed the fan clutch as well as the radiator cap....

HELP ME PLEASE...I AM GOING CRAZY..

Thanks Steve

 

[dfreeman616]

does the electric cooling fan turn on when you turn on the a/c?

 

[BOLO1994]

the fan appears to be working fine. It engages either when I turn the AC on or when the car reaches about 210 degrees.

 

[jayuu]

time for a 3 row

 

[RichP]

I'm guessing that you have taken care of this jeep yourself since you got it. When you have done the cooling system did you use tap water and anti-freeze ? Over time the tap water could lead to a build up of mineral deposits throughout the engine, kind of like chrome plating. Strange as it may sound bad grounds can cause problems, the cooling system with a high mineral content can become part of the electrical system, electricity takes the path of least resistance and if your main grounds are bad the system will find another route and if it's thru your cooling system it will use it. You have done all the stuff, replaced things, the only other mechanical thing that comes to mind is the radiator may be not working well due to age, the fins do degrade in additon to the tubes getting plugged. You need a flexable bore scope to see into the XJ's radiator thru that damned dog leg, I actually looked at mine a few months ago and the tubes were pretty clear, clear enough that I did not install the new radiator I had ready to go. Arizona though with those temps I'm seeing on the news, gotta wonder what the temp range is on a detroit designed automotive cooling system, ambient temp of 100 is one thing, ambient temp of 115 is another whole story.
Also as far as flushing the system goes, I am a fan of the prestone 7 hour stuff, that is amazing, it disolves the build up, not sand blast it like the quickie 15 min or 30 minute flushes.

 

[BOLO1994]

Thanks for the input all. I don' remember using tap water in the radiator, usually distilled/antifreeze. Regardless, I do agree that a new radiator is probably in order, but do you have a possible explanation for the erratic jump from the 1st line just past 210 degrees and the first red line? Could it be some sort of default computer setting to avoid extreme overheating or something? I just ran the car up to the same tempurature of pevious overheating alarm onset and again it made and erratic jump of approximately 20 degrees to the first redline. I blocked off the grill of the vehicle and idled the car for a while with the AC running to get the temp up. It happened just like every other time and all I had to due was turn off the AC and hit the heater. about 10 to 15 seconds passed and the temp dropped back to just below the 220 mark.:wierd:

 

[RichP]

No but then the gauges are not exaclty accurate, did you do a new pressure cap too and if so how many pounds, does the overlow bottle start to fill up ?

 

[BOLO1994]

I have replaced the radiator cap. 16lbs is the rating, same as the one I replaced. The overflow tank appears to be working as well. when I burped the sytem. It draws coolant to fill the system. When this problem first started I did have a couple incidents where you could see boiling over in the overflow tank. The cap I replaced was at least a couple of years old.

 

[BOLO1994]

I have replaced the radiator cap. 16lbs is the rating, same as the one I replaced. The overflow tank appears to be working as well. when I burped the sytem. It draws coolant to fill the system. When this problem first started I did have a couple incidents where you could see boiling over in the overflow tank. The cap I replaced was at least a couple of years old. Now there is no sign of boiling over in the tank upon overheating onset.

 

[RichP]

The only other thing that comes to mind is belt tension. A while back I got into a discussion with one of my customers who has large auto repair place, I built the 8 computers he uses for the snap on shop key system and the reprograming system he just got. I swore by the serp tension gauge, Krikitt from napa, he said he'd been doing it so long he didn't need the gauge. He just happened to have 3 4.0 jeeps in there that got new waterpumps and other parts and new belts so I walked over and checked em, he had em cranked to 80-90lbs when they should have been ~180lbs. Thats about the only other thing I can think of.

 

[BOLO1994]

Thanks for your all your help. I had to adjust the tension to get rid of the squeal at start up. I willl double check lbs.

 

[BlackXJ98]

BOLO
Any luck on your overheating problem? I have the exact same condition and have done all the same remedies, except the water pump. But no A/C, no problem, so I'm thinking it's the radiator.