Need help bad with XJ overheating problem...out of ideas!!

[irish1371]

I would double check to make sure you have the correct head gasket on with the right side up. I have yet to have to pull a 4.0 head so I'mnot totally sure if it is possible to flip em. But you may have gotten a wrong year gasket with the wrong steam holes in it.

Since this started when you changed the head i WOULD LOOK AT THE THINGS YOU DID WHEN YOU CHANGED OUT THAT OLD CRACKED HEAD. Where did the replacement come from? was it cleaned out is the head the correct one? Did you change anything else when you did the head swap?

 

[expeditionxj]

I would double check to make sure you have the correct head gasket on with the right side up. I have yet to have to pull a 4.0 head so I'mnot totally sure if it is possible to flip em. But you may have gotten a wrong year gasket with the wrong steam holes in it.

Since this started when you changed the head i WOULD LOOK AT THE THINGS YOU DID WHEN YOU CHANGED OUT THAT OLD CRACKED HEAD. Where did the replacement come from? was it cleaned out is the head the correct one? Did you change anything else when you did the head swap?

Remanufactured engine came with head installed. The bad head on the old motor ruined all the bearings so I went with a long block with the head on it. It did however come with the 0331 head on it, they supposedly magnafluxed it to test for cracks when they rebuilt it.... Who really knows though.

 

[jeep-N-montero]

As mentioned and as I inquired, the radiator is likely the culprit due to the coolant not being allowed to cool enough before being reheated by the engine. I run an OEM all copper radiator with a 70%water/30% coolant mixture with a bottle of Water Wetter and even with our 100+degree temps and the A/C on I don't have any issues.

 

[docwatson]

I've installed hood vents on two cherokees and saw no change in the temperature gauge. Added a bottle of Water Wetter as suggested and change my ration to 60%water/40%coolant and my gauge never went over 200 degrees, even when driving up mountain passes.

Sounds like the radiator is the cooling component to blame, but I would change the antifreeze mix for added insurance.

 

[expeditionxj]

Put in a 1 row 1.5" core oem style radiator today. Still a little air in the system, but seems to be running hotter than before.

 

[docwatson]

Put in a 1 row 1.5" core oem style radiator today. Still a little air in the system, but seems to be running hotter than before.

What mixture of water and coolant did you put in it?

 

[1stDeuce]

I don't have an XJ in front of me right now, but does the engine driven fan run the same direction on an XJ and a ZJ? I don't think mechanical fan clutches work if you spin them backwards, they just free-wheel, which means your mechanical fan may never be working. If you used two of the stock XJ fans for "all electric", be aware that those little fans don't move nearly as much air as the mechanical fan, so that might not be enough. (Was it better?)

Also, I'll concur that you may have a radiator efficiency problem (just because it is expensive doesn't mean it's any good...) or a head gasket problem. (can the wrong or upside-down head gasket block coolant holes on a 4.0L??? I'm not sure...)

Also, if you have AC, you need to make sure the A/C condenser can flow air and isn't all full of mud, or the fins smashed so as to block airflow to the radiator. Oh, and that there isn't a bunch of leaves and junk between the condenser and the radiator. (common problem on diesel trucks with giant fans, but usually not on XJ's, though if you spend time driving through corn fields, it can be...

A stock 4.0 XJ shouldn't run hot no matter what you're doing to it unless the ambient is over 110 or so and you're pulling something HEAVY.

Good luck!!
Chris

 

[expeditionxj]

I don't have an XJ in front of me right now, but does the engine driven fan run the same direction on an XJ and a ZJ? I don't think mechanical fan clutches work if you spin them backwards, they just free-wheel, which means your mechanical fan may never be working. If you used two of the stock XJ fans for "all electric", be aware that those little fans don't move nearly as much air as the mechanical fan, so that might not be enough. (Was it better?)

Also, I'll concur that you may have a radiator efficiency problem (just because it is expensive doesn't mean it's any good...) or a head gasket problem. (can the wrong or upside-down head gasket block coolant holes on a 4.0L??? I'm not sure...)

Also, if you have AC, you need to make sure the A/C condenser can flow air and isn't all full of mud, or the fins smashed so as to block airflow to the radiator. Oh, and that there isn't a bunch of leaves and junk between the condenser and the radiator. (common problem on diesel trucks with giant fans, but usually not on XJ's, though if you spend time driving through corn fields, it can be...

A stock 4.0 XJ shouldn't run hot no matter what you're doing to it unless the ambient is over 110 or so and you're pulling something HEAVY.

Good luck!!
Chris

Fans are definitely pulling air, the ZJ fan clutch is like a tornado under the hood, it's also a very popular upgrade to the xj so they must go the same direction and the electric works well also. The a/c condenser is brand new and has no debris in it.

Only lost about 6 qts. of coolant with the radiator change. Put back in a 60% water 40% antifreeze mix but don't have a working tester to test the overall mixture right now.

 

[docwatson]

Fans are definitely pulling air, the ZJ fan clutch is like a tornado under the hood, it's also a very popular upgrade to the xj so they must go the same direction and the electric works well also. The a/c condenser is brand new and has no debris in it.

Only lost about 6 qts. of coolant with the radiator change. Put back in a 60% water 40% antifreeze mix but don't have a working tester to test the overall mixture right now.

What are your temperatures looking like now?

 

[expeditionxj]

What are your temperatures looking like now?

Just driving around town this morning the ScanGauge was showing around 200 degrees, this is with a 195 thermostat. Although normal driving has not always been the issue, normally its under load where the issue pops up.

Also seems like once everything gets heat soaked it wont cool down nearly as good, like if I drove around town for an hour it might be running closer to 210 after a while into the drive.

 

[eflosd]

I was fighting the same problem very recently, it was all good around town and for the most part on the freeway, but when I would pull long grades or backr roads going to the trails it would heat up quick. I added hood spacers which seemed to help a bit. I can understand you dont want to do this but i removed the a/c condenser (A/c never worked in my 96) that lowered the temps about 10 deg. i see you replaced the pre cats, any other exhaust leaks (header)? hows the main cat? auto or manual trans? tire size and axle gear ratios? I added a switch to manually lock the torque converter on my aw4 so I can pull hills in 3rd and be sure its locked up which also helped

 

[taiden]

What's this about a water pump "moving the coolant too fast for the radiator to cool it"

Similarly, the water pump will "move the coolant too fast for the engine to heat it"

One could make this same argument about a low coolant flow rate, except that the coolant in the block would boil out before it had a chance to get to the radiator, thus causing the water pump efficiency to plummet.

The only realistic problem created with a water pump moving too fast would be cavitation at the blades, which causes pump efficiency to drop. This usually only shows up if the design of the blades is poor, the pump is being overdriven, or the RPMs are quite high... or any combination of all three.

 

[docwatson]

So are your arguing that the speed of the coolant plays no factor in the cooling of the motor?

No one is saying the coolant should be near stagnant when flowing the system. What I (and I believe Black ZJ) are saying is that there is an optimum speed. Too fast the fluid doesn't cool enough or draw enough heat, too slow and, as you said, the fluid boils out.

OP, did you flush the system when you changed everything or just refill?

 

[taiden]

http://en.wikipedia.org/wiki/Heat_transfer_coefficient

Fluid flow rate is not a consideration when calculating heat transfer between a solid body and a fluid.

So we can rule the idea of excessive coolant flow rate out, as long as there is no cavitation at the pump blades, which would nearly halt coolant flow rate at high pump speeds.


Anyone else find it strange that this only happens under load?

expeditionxj, you said it can overheat in a manner of seconds under load... does it overheat if you go wide open throttle for the same amount of time? (Open loop, rich. Would rule out a bad O2 sensor. Is your gas mileage abnormally good? Do you get a lean hesitation?)

Have you checked the basic stuff... timing and fuel pressure? Do you have any way to test if your XJ is running exceptionally lean in your low load situations?

 

[docwatson]

Q = heat transfer rate in Joule/second meaning time is factor in the equation. So although flow rate doesn't enter the equation time does and exposure to both the heat of the engine and coolness of radiator affect effective cooling of coolant.

Taiden does bring up a good point about running lean though as that, I believe, increases operating temperature. 200 seems a pretty average for where the XJ would be operating. How high do the temps get under load?