Cooling issues/bad head gasket?

Ok I've done many extensive searches and have found many many useful tips and plenty of advice but I am still having a problem.

It's a 96 Jeep cherokee with the AW4, 231, 4.0 yadayada. When I got it a year ago I had some slight cooling issues nothing big, I knew that cherokees are notorious for having cooling issues so the goal was to replace everything anyways. Jump ahead to last September and this is what is new.

Water Pump
Fan Clutch
Radiator
Thermostat

At this point it runs perfect and has not gone over the middle line even once. So I think problem solved. Now jump ahead to about a month ago.

I was out with some buddies in their large "back field" when the jeep overheated alllllll the way and it blew a hose off the radiator to warn me sense I was oblivious to the gauge. It refused to cool at idle and even when we wetted the radiator. Reluctantly I had to turn off the engine to let it cool down. After letting it sit we started it up and it ran bad, really really bad. I thought it was toast. We put water back in it and let it run for a while but it kept overheating slightly. The check engine light came on at this time and later I found that the electric fan would not turn on. At this point it started to run fine again? Also there is no coolant in the oil nor is there visible oil in the coolant. I checked the relay and it seemed fine. No resistance when it clicked over. I ended up hard wiring the fan with an inline fuse just to be able to drive the jeep. This solved the at idle overheating problem but the thing still overheats anytime I run at more than 2000RPM on the highway or when I am cruising up hills. Had the check engine light tested and it said the EGR valve had some problem.

So yesterday I bought a new fan switch/sensor the temp sensor on the T-stat housing. I had to buy one for a 2000 jeep as the ones for 96-99 did not have the right connector? Put that in and the fan still doenst work. It does come on with the AC. Also the check engine light went off. Then I took my jeep to a buddies shop and we checked the radiator for exhaust gasses and it tested positive. So I guess my question is: Is my overheating problem caused by a small head gasket leak or am I missing something simple. Any ideas? Thanks!

If you have a leaking head gasket or worse, a cracked head, it's probably the egg rather than the chicken i.e. it was caused by the overheating. Do a compression check on all cylinders. If you have low compression on two adjacent cylinders, you probably have a blown head gasket. If only one cylinder has low compression, it could be blown gasket or cracked head. Does steam come out of the exhaust?
The overheating was probably caused by the electric fan failing to switch on, and since the fan relay works (if it didn't, the fan wouldn't switch on when you operate the A/C), the root cause of the problem is a bad coolant temp. sensor (the one that you replaced in the t'stat housing). Make sure you get the correct replacement unit and check the wiring for any cracks/breaks.

Thats a great idea about the compression check. There is no steam in the exhaust nor does it have that sweet collant smell to it. It would be unusual that the fan swith is bad because I just replaced it yesterday but I will veryfy that the wiring is complete and intact. When I put the new sensor in the Check Engine light went off so I figured they were related. I will do the comp check and get back with the results. It doesn't appear to difficult to change the head gasket is there anything I should know about it? Any particular gasket I should choose. I expect it will be in the $80 for a new gasket has anyone bought one recently? Thanks again.

Oh yeah one last thing what is the correct sensor for my jeep. Both autozon and napas 96 jeep cherokee sensors have the wrong connector. Autozones 97-99 sensors are the same as their 96's. Napa doesn't list a 97-99 sensor and both Autozone and Napa have the same sensor for 2000-up which appears to be the correct sensor visually and connection wise. Thats the one I used and it turned off the check engine light.

If it turns out that you do indeed have a head gasket leak, check the head surface for flatness. Overheating can cause the head to warp so you might need to get it milled. Go for the Mopar performance 4529242 head gasket. It's 0.008" thinner than the OEM gasket so it'll raise the CR by 0.15 and give you an extra pony or two.
If you're in doubt about the sensor, just get an OEM replacement from the stealership. That way you'll know for sure that you have the correct one.

If you have a way to measure your radiator's temp, it should be very close to the in-dash gauge's reading. Otherwise the sensor is bad or the wrong one.
There is only one temp sensor in the 2000; and the PCM commands the gauge and the fan according to its reading.

Ok this is up from the dead but the problem remains. I have the jeep all back together with new head gasket and resurfaced head. With the aux fan hardwired it STILL overheats. I've checked the flow and everything seems to be ok. How do I check the water passageways in the engine block itself? The radiator itself and all the hoses are clear.

Once again its got a new:
Radiator
Thermostat
Waterpump
Fanclutch
Headgasket

It overheats exactly like it did when it had a bad head gasket.
I thought I heard once about a waterpump that pumps the wrong direction could that be a problem? Whats next on my list of things to eliminate/check?
Oh yeah I bypassed the heater core just to check and that fixed nothing. Thanks guys I really hope you can help me get through this I am getting so tired of not being able to drive my jeep anywhere.

I have the same EXACT probblem as you, but havent dropped the dough for a HG job yet.

Try removing the trans from the cooling loop and run it on its own trans cooler.

Fergie

Good idea I was thinking about that doing just for kicks. Did that do anything for you?

Has anybody accidentally bought one the the reverse flow waterpumps when buying a new water pump?

It seems like it must be something along those lines, this problem just isn't making much sense. It must be someting very obvious for me to keep missing it.

Could be a cracked head as oppossed to a HG too.

Are you still losing coolant?

Fergie

I never have lost coolant. The head gasket leak was SOOOO tiny no water got in/no oil got out just some exhaust gasses got into the radiator. When hooked up to a pressure tester it came up to normal and maintained normal. The one and only reason I knew there was a leak was because I did the exhaust in the radiator test on an off chance there was a leak and there was.

Huh, I was just told by a mechanic that the "hydrocarbon in the radiator" test is a 50/50 shot, and that false negatives are often received.

I'm gonna do a pressure test after I change my oil(nothing weird in the oil) and see if the pressure test can determine everything, but I am at a loss also.

What year is yours BTW?

Fergie

Well that leads me to believe that I could have replaced the head gasket for nothing. HAHA. Oh well. Mine is a 96 how about yours?

1995.

However, I am losing coolant, slowly, and can smell it.

Fergie

Static, how much did the head gasket end up costing you? and where did you get it?

I had the same issues with my 93. Initially it started out with slightly higher than normal temp readings. It kept getting worse I swapped t-stats, the waterpump (which was fine), had the rad. flow tested, and checked the lower hose for pinching off. Nothing fixed the issue. By that time it was getting up to 250-260 on the freeway under load and not cooling off when pulling over. Lots of bubbles in the radiator. Did compression test, 140-145 on all six and oil clean. It looked like a small head gasket leak. So, I yanked the head and the gasket looked questionable. Then put a different head on that was already milled and magnafluxed. I put on a new Fel Pro gasket. Fired it up and ran perfect, I burped the system while it warmed and watched the coolant with the cap off. At 190 or so it began bubbling and it worsened to the point of spraying out in spurts at piston speed. Nice, just what I wanted to see! So the only other option is a small crack somewhere in the block letting compression/exhaust into the waterjacket after the motor heats up. With the head off again, I finally found a crack that was about 1/2 inch long in #3 right above the piston at BDC. It was barely noticeable. So I pretty much had to start over with another block. Get a test done to check for hydrocarbons in the coolant, then you can rule out all other options besides head gasket or cracked head/block. I've never heard of theses blocks cracking besides getting frozen!

FUNKYTEE5

It cost $60 bucks to get the head milled and another $100 or so for the head kit. I got the gasket from Baxter Auto parts. I will do another hydrocarbon check this weekend when I have a spare moment. I sincerely hope it is not a cracked block. I have let it warm up with the cap off and never noticed it dump coolant in any regular pattern, so that is hopefull.

Here is another situation to add to the the list. When I let the jeep warm up and I watch the gauge, the needle slowly moves up to the middle and then drops back down a bunch which I assume is the thermostat opening but then it rises again, more and more until it starts to move over the line. I have not let it run more than about 10 degrees above the line because I don't want to hurt it since I just changed the gasket.

No help from me this time, but I am getting my XJ tested on Friday, so I hope to come back with good results.

Honestly, I am lost as to why I am losing/smelling coolant and overheating, so hopefully we can both get our OH problems resolved soon.

Fergie

staticrevolution said:

It cost $60 bucks to get the head milled and another $100 or so for the head kit. I got the gasket from Baxter Auto parts. I will do another hydrocarbon check this weekend when I have a spare moment. I sincerely hope it is not a cracked block. I have let it warm up with the cap off and never noticed it dump coolant in any regular pattern, so that is hopefull.

Here is another situation to add to the the list. When I let the jeep warm up and I watch the gauge, the needle slowly moves up to the middle and then drops back down a bunch which I assume is the thermostat opening but then it rises again, more and more until it starts to move over the line. I have not let it run more than about 10 degrees above the line because I don't want to hurt it since I just changed the gasket.

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Check your temp. with a analog gauge/infrared tool to confirm the accuracy of the factory gauge, to be safe!

Where/how should I check it and what will that tell me?

Get ahold of a laser/infrared temp probe, and shoot it at the coolant, radiator hose, block, etc... If you don't have one of them get some type of thermometer and stick it in the coolant just to verify the dash gauge reading. It's always to check stuff x2 with methods before tearing something down!