Hello,
I have a 1990 XJ (closed radiator system) and I have been having overheating problems lately. I just replaced my thermostat with a new one (190F) and drilled 2 small holes in it to "burp" the air out. After I did this, I used the vehicle for a while and still am having overheating problems.

Anyone got any ideas on the next thing I should try and check? Thanks.

 

A defective thermostat will only cause problems if stuck closed, what is the ignition timing set at? cylinder compression?

 

When you had it apart swapping the T-stat, did you flush the whole cooling system out really good? You most likely have a corrosion/rust clog somewhere in the motor or the radiator itself.

 

I am buying a jeep with this problem, they have taken out the thermostat, but still having problems, it just started one day a few weeks ago. they are going to replace the cap on the reservoir. But, I would like to know more.

 

I've owned my XJ for a little over a year and flushed the cooling system twice. For whatever reason, the cooling systems in these things really gunk up, and a Chrysler service advisor confimred that fact to me. (Although, I'm not sure about the Renix system) Take a look at your cooling over flow bottle to see what I'm talking about. If it's beyond a flush, it could be your radiator. But you should start with flushing and proper maintenance. To me replacing items like hoses, thermostat and water pump are not a "wait until they break" maintenance item, but rather something you do as a preventative measure. I have to depend on my Jeep to get me back and forth to Texas pulling a trailer, and the idea of a $50 part causing me a tow and delaying my travel is not a good one. Here's a good artical on radiators and cooling systems, and it's pretty much the steps I'd take if I was having your issue.

http://www.ehow.com/how_4856078_trou...-radiator.html

Also, I'm a firm believer on these XJs that a Mopar thermostat is the way to go. Get rid of the one you drilled two holes in and spend $8 on a good one.

 

I had this same problem and couldnt figure it out either. i ended up replacing my radiator with a u-pull-it part for 40 bucks. and that did it. I was told its the thiner veins in the radiator its self that clog and dont allow flow through the system. Also check your water pump it could be bad and not circulating.

 

Another thing I didn't mention before is that the OEM radiator design in XJs is pretty much junk. I mean aluminum fins that are too small and PLASTIC side tanks. What were these guys thinking? I know, that the radiators would last about 10 minutes especially when trying to keep the 4.0 cool and you would have to buy 3 new ones from them a year...LOL. I installed an all metal 3 core radiator from CFS Radiator in my XJ and it works great! The price wasn't too bad either.

 

So First we need to check the:

Thermo - if its closed
Reservoir cap
Radiator
water pump
??

 

check the electric fan, went on mine and overheated until i narrowed it down. replaced water pump and thermo before realized what was up

 

I did one flush, but it was probably not done well. I did the "quick/liquid" method without using the hardware that others recommended.

 

I did a home flush on my '88 a few weeks ago - the sludge that came out was dirt brown. After putting in fresh coolant the heater blew nice & hot for about a day. After that day some more sludge must have moved around the system & clogged my heater core again.

I just had a pro-flush yesterday & once again have heat. Talking to the radiator shop guy he stated that these engines are bad for sludge build up & the heater core especially is renowned for acting as a filter & trapping all the gunk.

I'd recommend a pro-flush (uses much higher pressure than a garden hose can generate) - if that doesn't work it sounds like either a new rad or water pump is required.

Just thinking outloud here but I have heard of water pumps mounted incorrectly so that they do not circulate coolant correctly.

 

i bought my '88 just a few weeks ago... and it had a pretty gnarly overheating problems too.. if you already changed out the thermo. next best thing to replace is the water pump,, if that doesnt do it and you got some cash change out the radiator from a '91 plus i picked one up from advanced auto parts it is an aluminum single row for about 130+ tax but the only diff. is that it came w/ a radiator cap and now my heat blows warm and takes a good half hour or so for it to hit 210 degrees
good luck!!

 

I have a problem with Jeep overheating too!

I had been driving through town for about 20 min, stopped to put in gas, left the station and hit the highway. When my speed had been at 120 Kph (+-55 Mph) for about 1 min I noticed the temp gauge climbing.
By the time I was able to pull to the side, slow down and switch the engine off, about 20 sec later, the gauge was almost on the red! It was probably at about 120 degrees celcius!
I had her taken home on a truck and started troubleshooting. Notice a very slight leak on the radiator side of the fat pipe that lays over the battery (Attaches to the radiator on the opposite side to the cap and enters the top of the engine.)
I sorted the leak out and it is now fine.
I tried to 'burp' the system by jacking the front of the vehicle up and removing the radiator cap then running the engine until it reaches operating temp.
The vehicle runs perfectly and doesn't overheat when the cap is removed. I closed the cap and continued to idle the engine for about 3 min with both fans running. Everything was looking good!
When I switched the engine off and restarted the vehicle about 5 min later it overheated again!
At idle the temp just keeps climbing.

Is there any significance in the fact that it runs without overheating when the cap is removed?

Thanks for the help!

 

So... the Radiator specialist tells me the radiator is finished and that I need to buy a new one from him.
I shop around, buy a new Aluminum radiator and install it today - hoping that this will be the end of my troubles!

NOT SO LUCKY!!!

Still overheating!

So now I have new t-stat and new radiator.
Next up, water pump?
How should I test the pump?

Thanks for all the help!

 

I had the exact same problem bought an 89 XJ that was over heating replaced the head gasket and water pump. Still overheating and blowing the cap off the bottle. Finally I did some researcha and found that the temp switch that turns on the electric fan is in a postion that when it knows to turn on it is too late. Also air will get trapped in the bock and the best way to get it out is to jack the back up high enough to get the temp gauuge sensor higher than the thermostat and burp it that way. Finally fixed it and my daughter was pushed into another vehicle and punctured the radiator. So instead of trying to go through all the steps again I converted it to the open system that is in the 92 XJ about $200.00 for the radiator the overflow bottle and the valve and have never had a problem since. I still have the electric fan hot wired to the ignition so that when the vehicle is started it is running. Not taking any more chances. I have already had the head off and checked 3 times. Also these heads are not very forgiving and will crack. If you have overheated it. Spend the time and money to have the head magnufuxed and re-plained. You will not regret it.