I am unsure of whats going on to be completely honest.. we have another XJ.. its a 1995 Cherokee SE with the 4.0HO. i have been noticing a slow coolant leak without any signs of dripping or coolant puddles on the ground. I have pressured tested it until i cant anymore and i finally found what appeared to be a leak, the top part of the lower radiator hose. I have in all replaced the upper and lower radiator hoses, the heater control valve and all the hoses connected to that within this month so i know those are all new. I filled my over flow back up and the radiator up and it appears to have dropped again in the over flow again slightly in the past day. I havent pressure tested it yet but i still cant seem to see any coolant leak ANYWHERE on the ground.. I pulled the spark plugs today to see if there was any obvious coolant and i saw nothing except one plug on cylinder 5 looked a little black as if it were burnt.(I put all new plugs in about a month ago) i did not see any coolant on the plugs. i smelled my exhaust and i cant tell what im smelling because at this point i dont have a catalytic converter so im not sure if that makes a difference on smell? i wiped the end of the tailpipe with a rag and it was all black and i didnt smell any coolant. I am not sure where else to check or what else to do... Any help is VERY appreciated. im ready to hit my head against a wall...

thank you

 

Pressure test will tell you a lot. I had a cracked head last winter, and I had the mysterious disappearing coolant too. Make sure you do it right the first time, as I didn't and ended up spending about $2500 total to fix it.

 

Anytime you remove the radiator cap the coolant level in the expansion tank will drop slightly.

 

You can use a sniffer that you put on the radiator. What it does is detect exhaust in your cooling system. If that test shows exhaust in your cooling system then you can be assured 100% that your head is toast or the head gasket is toast.

http://www.napaonline.com/Catalog/Ca...006_0361073538


If you have any contacts in a repair shop with an exhaust gas analyzer they can put the tailpipe sniffer in your overflow bottle / radiator fill neck and do the same test.

 

A simple compression test will show if you have head/head gasket problems.

 

Good advice Andrew. This is what I would do if this were my XJ. Good data point.

The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.

 

Did ya test the cap also ?

 

My understanding was that the compression test could diagnose valve train issue. Would it also help with diagnosing a cracked cylinder head?

 

If you have coolant on the lower radiator hose it could be coming from the water pump. Check the water pump carefully. you also want to make sure any hose clamps are tight enough not to leak. Be careful on the clamps at the radiator. You don't want to break any plastic there.

 

Well after a bunch of tests I can hear a very small leak when it's under the compression tester. The leak was only air, I did not see coolant coming out but it was by the upper radiator hose, on the top part connected to the radiator.. I pulled the hose off and tightened the clamp as tight as it'll get and I still hear the leak... Any suggestions?