Chuck

I have a 97 4.0 High Output Automatic XJ that is overheating.

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 - one immediately thinks fan clutch but the problem started when I was doing 120Kph so I seriously doubt it being the fan!

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

Thanks for the help!

Chuck

I pulled the t-stat out today - seems to be the problem! Popped it in some boiling water and waited! Nothing!
Its stuck closed. Explains all my problems! I idled the engine for a while with the t-stat removed and the temp seems to be fine.

Thanks for all the advice!
Ill set out flushing the system tomorrow - just for good measure! Then pop a new t-stat in and see what happens!

Thanks again!

Chuck

Thermostat replaced, put everything back together and filled the system. Burped it etc.

Still overheating! As well as a 'Check engine' light!

Missfiring and coughing and spluttering for about 20 sec after start. Then idles ok-ish.

Im thinking that perhaps my Headgasket is leaking water into the exhaust system? Possible?

I drove her - slowly, Stop, starting to a Radiator specialist today. He says the radiator is probably blocked - I must pull it out and leave with them for 'proper cleaning' and testing. Ill drop it off there tomorrow and see what he says!

Ill be honest with you... Im stressing!

Any thoughts? head gasket or radiator - what do you folks think?

95Cherokee

If it's the radiator go ahead and buy a new one, might as well get an aluminum one while you're at it.

fantic238

How did you burp the system?

Chuck

Hi there fantic 238 - I burped the system by switching it on and running until it reaches +-105 degress celcius without the rad cap on. I got this method from the FSM.

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!

LCFRJEEP

If the waterpump is leaking out of the bottom through the weep hole that I would replace it. If it tends to overheat at speed or when driving versus when at idle I would say replace it. If it overheats when you at idle, I would replace the mechanical fan clutch. I have gone through the same issues you have with my 95 XJ and I ended up replacing everything (rad, waterpump, t-stat, t-stat housing, fan clutch, hoses and flushed the hell out of the system). I replaced my rad with a 3 core/ all metal radiator from Radiatorbarn.com. I HIGHLY recomend this rad as an upgrade or replacement.

fantic238

If the water pump is not leaking there are only two options left: not burped well or bad head gasket.

fantic238

Does the electric fan come on?

Chuck

Electric/Aux fan is linked to a manual switch on the dash so that aint an indicator unfortunately.

About to check to remove the t-stat to see if there is water flow without it installed. This should ascertain whether or not the pump is working - correct?

Then when I re-install the T-stat Ill make double sure its in the right way!

fantic238

Does it overheat also with the el fan on?

Chuck

Yes - on or off makes no difference! Also overheats when moving at speed.

I just ran the engine without the t-stat in. Still no water in the 'hot' upper radiator pipe. Feels empty although there may be a trickle passing through it!

Im thinking its definitely the water pump. What are your thoughts?

RENIXBEAST

I had the same problem with mine. I put new lines, new thermostat, new water pump, my radiator looked fine and wasnt blocked, but it wasnt doing its job!!!! I installed a new stock radiator 130$ and I havent had a problem since. I dont even use my electric fan anymore.

RENIXBEAST

If you buy a new water pump don't get it from NAPA. I went through 3 before they gave me one that was actually good. I could change one with my eyes closed now.

RENIXBEAST

My water pump wasnt leaking but it was still faulty, It was still pumping, just not enough output.