How hot is the water in the radiator? Any steam if you loosen the radiator cap?

Its hoooot steam coming out of the over flow and its somewhat boiling.

IIRC, you've replaced the t-stat, water pump and had the rad rodded out.....made out like a bandit so far, at only $60............but still diagnosing.

Does anyone know a nifty test of the fan clutch? Can you heat it with boiling water and feel it get stiff/build resistance ?

my old fan clutch didnt work to god, i couldnt see it was bad, but when i changed it to a new one it was totaly different. The fan clutch run at high speed when starting up and for 2-3 min (maybe the "thing" inside need to warm up to work?), then it slows down and dont go in high speed before the radiator is hot again. When its running in full speed you will hear it inside your car, the noise from the fan is higher than the noise from the engine at 2,5-3k rpm, the air flow is high inside the engine, you cant hold your hand relaxed in the airflow, i could do that before but not now.

It's a somewhat long drawn-out test proceedure in the FSM. AT +/-$35, the fan clutch can be considered a disposable maintenance item. Their efficiency slowly degrades starting the day it's installed.

I can agree with this statement 100%. I installed a brand new one and it went bad in 2 weeks after one 4 wheeling trip. I guess the water bound it up. I got rid of it and did electric fans that I now can shut off whenever I need to.

Well....on the other hand they can last a very long time. At least 12 years, 140,000 K. I meant to spin mine today. It's a good climb, 1,500 ft, to my house, I want to see how it feels hot, but forgot. If he could test his he could avoid canning a potentiality good, (or even better then "new") unit, as well as homeing in on his problem.

One can test 'til blue in the face. There's no way a 12 yr old silicone fan clutch is as efficient as a new clutch. Their efficiency slowly degrades with time/miles. The OP can eliminate the clutch with a solid spacer....hear a lot of noise and probably get no better engine cooling 'til he replaces the fan shroud. Will he instantly gain a cooler running motor?....probably not, I think there are other issues involved. The XJ cooling system is mediocre at best....all components must be top notch condition, especially under extreme operating conditions like 110F ambient.

Agreed he may well have other issues. No doubt though he should see that air is passing through his radiator. He'll want to end up with that anyway.

AZ, where you able to do the power-brake test? Once my (84/ 2.5) shot water out the filler like a geyser. Head gasket was Swiss cheese!

How do you do the power-brake test? Ill def try it.

I don't have any symptoms of a bad head gasket though.

Well...overheating IS a symptom of a bad head gasket. Those combustion gasses are very hot. Up to 3000*. If that leaks into the water jacket it does tend to warm things up a tad. Is why this test:


Get it just as full as you possibly can, to the tippy top. With the cap off and your foot firmly on the brake give it some throttle in drive. Just for a few seconds, maybe the count of five. Once on a really bad one the geyser hit the hood! Or if it bubbles that's an indication of a bad gasket also. Some amount of surge might be normal, but if it keeps up/bubbling that's not good.

Of course you will use common sense and not run your Jeep into something or somebody! Right?

You're gonna need a shroud someday, might as well handle that. Also never hurts to do a compression test. That might help point you.

I thought a cooling system pressure test had already been performed, pressure held and passed, no? Wouldn't a bad head gasket fail the pressure test?

I already pressure tested the head, and it passed.. and the cooling system.

"I already pressure tested the head, and it passed." OH...I'd still do the 2 minute power-brake test. Combustion pressures are WAY higher then anything you would expose your cooling system to. OK, maybe counting filling it 3 minutes.