96 XJ Overheating

[stewie]

The Stats:

96 XJ
4.0L
AW4 swapped to 4WD/ 231
D30/8.25 4.56 gears
35" KM2s

Cooling system:
New NAPA water pump
New NAPA T-stat and housing
Newer radiator hoses (lower does not have the spring- good luck finding one with a spring)
New CSF 3 core copper/brass radiator
New "ZJ" (though NAPA lists it as a 4cyl XJ part now not a ZJ part) mech fan clutch
New heater hoses from front of motor to heater core
Chemically flushed recently and water flushed multiple times since I got her in Dec 2010.
Trans cooler bypassing the radiator (don't get started on over cooling the trans- I'm in Phoenix, it ain't going to happen)
ZJ trans cooler used as power steering cooler for WJ ps pump mounted in front of electric fan

Problem:
It started when I was towing my pop-up tent trailer through the mountains on my way to the AZ chapters event back in March. I started to overheat so I turned off the AC (I didnt have the big ole hole covered from my novak shifter so a ton of heat was getting into the Jeep) and turned on the heater to defrost. That helped on everything but the big long grades. At the top I would have to stop and let her idle to cool down. The Jeep did good for the weekend wheeling with no problems overheating. Most of what I was doing did not require a lot of throttle. The ride home was a lot more down hill than the ride up but still had uphill grades and the process had to be repeated again, but not as much.

Now, she overheats with city driving and highway travel is out of the question. I ditched the taurus fan and put in the ZJ fan clutch and new radiator. No help. Replaced the rest. No result. She will idle fine in the drive way even with the AC cranked, but driving on the street, she will overheat. I do have a winch bumper (dirt bound offroad diy winch bumper) but the winch sits low and does not block much of the radiator at all and no lights on it.

I feared a head gasket leak so I did a block test (blue fluid that turns green with exhaust gases) and it was negative result. I just did a compression test and found the following reading cyl front to back in lbs.:
125
135
130
130
135
130

I do have a cracked manifold. The crack is at the typical location-on the tube closest to the motor at the weld where the two tubes join. But the crack is most pronounced away from the motor tapering to be hairline at 45* upwards towards the motor and then not cracked facing the block or under, so I doubt its shooting hot exhaust gases on the block. And this was checked with the motor running at temp with an inspection mirror.

I'm at my wits end with this. Its going to be getting cooler in a couple months and that means prime wheeling season here- opposite of the rest of the country, so I would love to nail this one down.

Thanks for the help
Stewie

[garr]

Did you replace the OEM Fan shroud when you ditched the the electric fan? it is important.

[stewie]

Yep, fan shroud is in there, was a PITA getting everything to fit (ZJ clutch, 3 core rad, shroud) but got it in there.

[stewie]

Just got done driving the XJ and its just as hot now even after all the maintenance as before we started. I am truly stumped. I'm wondering- head gasket? not enough air getting out of the engine bay now?

Thoughts, theories, ideas?

TIA
stewie

[Reclipse]

Gonna throw it out there, have you tried blowing out the condenser from the engine bay out? I know they usually fill up with bugs, grass, weeds, dead body parts, you know the usual stuff. Could very well be airflow is not getting through, therefor won't cool properly.

[stewie]

Ive flushed the condenser with water and its clear of debris save for some small stones, well sand particles really.

[weebur]

I don't know what state you reside in but a mixture of 40/60 (coolant/distilled water) and an addition of anti-corrosion additive) should give you better cooling and protection to about -10F.

[C85D4x4]

New Stant radiator cap.

[Icemans]

I would say check your cap to make sure you are staying around 15 to 16 lbs of pressure in the colling system. Also because it cools at idle but not when driving i would pull your water pump and check it. If its warn it might cause cavitation (http://en.m.wikipedia.org/wiki/Cavitation) which will cause it to not move enough water at high speeds and cause it to overheat. I would leave more toward the pump then the cap. Just my two cents.

[stewie]

Originally Posted by weebur

I don't know what state you reside in but a mixture of 40/60 (coolant/distilled water) and an addition of anti-corrosion additive) should give you better cooling and protection to about -10F.

I'm in Arizona and so far I have been running a 50/50 premixed green coolant. Whats the best way for accurately achieving a 40/60 mix?

Originally Posted by C85D4x4

New Stant radiator cap.

I had been running a new NAPA brand (mfg by Stant) cap. Its now about 4 weeks old.

Originally Posted by Icemans

I would say check your cap to make sure you are staying around 15 to 16 lbs of pressure in the colling system. Also because it cools at idle but not when driving i would pull your water pump and check it. If its warn it might cause cavitation (http://en.m.wikipedia.org/wiki/Cavitation) which will cause it to not move enough water at high speeds and cause it to overheat. I would leave more toward the pump then the cap. Just my two cents.

I replaced the water pump back in April with a new NAPA wp due to leaking at the wp output, so a worn out wp causing cavitation is not likely.

And on a side note it was 112* for a high in my city today.

[Icemans]

Originally Posted by stewie

I replaced the water pump back in April with a new NAPA wp due to leaking at the wp output, so a worn out wp causing cavitation is not likely.

And on a side note it was 112* for a high in my city today.

I guess it would help if i read your whole post sorry about that. You've done everything i can think of sorry man.

[#S194]

I would fix that exhaust leak. I have been having an overheating problem when climbing a grade that has been driving me nuts. EcoMike suggested I check my fuel pressure for a lean condition and check for an exhaust leak blowing hot air on the block from the collector.I had the down pipe replaced since it was pretty beat up and the flange was pretty wasted (it was the original pipe) from removing it a bunch of times. My fuel pressure was within spec, so no lean condition. I also added a ZJ fan clutch. Seems to run cooler now. The mechanical Auto Meter gauge I have installed in the water neck is reading around 185 to 190, which is about 10 degrees cooler than before. It's no where near as hot here as where you are but I have noticed a difference.

[garr]

Even Though you already replaced the radiator cap, I would replace it again,
lately it seems that Radiator Caps are notorious for defects/failing.

[Icemans]

Originally Posted by aquino#s194

The mechanical Auto Meter gauge I have installed in the water neck is reading around 185 to 190, which is about 10 degrees cooler than before. It's no where near as hot here as where you are but I have noticed a difference.

If your running at 190deg your not to hot. These rigs are set to run between 190 and 210. The aux fan on my rig kicks on at 210 from the factory.

[Planetcat]

Did you get the correct reverse rotation (i.e. counter clockwise) water pump? I just bought one at napa and it was designated standard rotation, but was in fact the correct pump. That would cause it for sure (wrong rotation). Heater core clogged? You can bypass the heater to see if that makes a difference. The belt could be tensioned too tight. It's worth noting, that on my original 96, I put a CSF 3 row radiator in my overheating XJ and it started hundreds of hours of electric fans, trouble shooting, etc. I eventually pulled it out and put in a one-row aluminum, and could tow my 4000 boat anywhere, anytime. I ran 32's and an RE 4.5" lift with 4.56 gears, AW4. My theory on the 3-row rads is that if you have the condenser and the trans cooler in front of the radiator, the air is so hot by the time it gets to row 2 and 3, that you essentially have a very narrow tubed one row radiator. Just a theory. Try my other suggestions first though.