Am writing this for my hubby who's not here right now, so please forgive errors. We have a 2002 Grand Cherokee Limited 4WD with about 87,000 miles. The other day while driving in late afternoon Florida heat, the A/C started blowing air at ambient temp instead of chilled. Sometime after arriving home or overnight (not sure exactly when) the car peed a bunch of water all over the garage floor, from the vicinity of the front passenger side. The next morning my husband found the water level in the overflow tank to be low, so filled that to the fill line, plus added water at another location in the cooling system (I forget the name - some bleeder port or something?), and also checked the radiator water level, which was full. He later learned that after filling he needed to leave the radiator cap off and port plug open and run the engine until it was hot, to eliminate air from the system -- which he did, outside on the driveway. At first, all he got was foam. Finally air bubbles appeared through the foam, and they continued to bubble on and on until he gave up and shut off the engine, making him think maybe there was some type of continuous air pressure affecting the cooling system. (I should tell you that sometime during this period he did check the A/C and it was cooling properly, so apparently this is not a refrigerant loss problem, or so we presume.) But here's what may be another important factor: When he went to hose off the driveway he noticed an oil film on the water that had accumulated. There has also been a fair amount of an oily substance in the overflow tank water! So here we are not knowing what's going on, and whether the car should be looked at by an A/C specialist or whether we should, as we've read elsewhere, think in terms of a head gasket diagnostic/possible replacement. Or could it be something else entirely? Any input appreciated!

 

This sounds to be a head gasket - the most likely culprit for putting oil and and the air in the coolant. The air would be exhaust gas leaking past a blown head gasket from the cylinder into the coolant passage, and into the radiator bubbling to the highest point.

(This statement is based upon what I have read, NOT personal experience)
Depending on your engine (4.7L V8, or 4.0L Straight-6), there are many discussions regarding occurrences of cracks in the cylinder head (stamped casting number 0331) used in this era of the 4.0L. Even with an intact head gasket, this will produce many of the same symptoms. I have not personally seen one of these cracked heads, but it seems to get a lot of attention on this forum and other Jeep forums. Improved/Corrected cylinder heads (TUPY) were produced beginning in the 2002 model year ( I can only assume that there may have been 2002 MY vehicles produced with the old 0331 casting). Apparently "TUPY" can be seen if you look down through the oil fill hole in the valve cover if it is in fact the corrected head casting.

A head gasket would be the ideal of the two scenarios whether performed by a shop or by yourself, but nonetheless not particularly cheap. Having to replace the head if it is cracked would have the added cost of the cylinder head itself, and the time to swap over the valvetrain (if a bare head is chosen).
Being in Canada and doing all of my repairs myself I cannot confidently give you a cost figure (hopefully somebody in the area may be able to chime in), but I am seeing replacement heads anywhere from 800CAD (reman) to 1200CAD ("New") for bare and complete heads - parts only.


On the A/C: I would recommend the first thing to check when the A/C starts blowing warm air when enabled, is to check whether the compressor is still running when this happens. Obviously you'd have to pull over and pop the hood to check this.

 

Thanks so much for your thoughtful and complete response, oddballracing. My husband has now read and seems to agree with your analysis. We need to find a shop qualified to do engine work, as our regular repair guys won't even do the diagnostics. Either that or we need to try to keep the car limping along until we see what funds may be available to purchase a newer vehicle once we accomplish a planned relocation close by. Ain't we got fun? Will come back here at some point and let you know what happened. Thanks again and best regards!

 

You are very welcome. As much as I hate to relay bad news, what you describe is not an easy repair. If you are going to limp the vehicle along in this condition, I recommend keeping a close eye on the oil condition (every one or two days)to ensure it isn't accumulating coolant in it. If you are seeing the coolant in the oil, and getting exhaust gas in the coolant, it is possible you wont get contamination the other direction (coolant in oil), it is a likely risk. If the oil starts looking like chocolate milk, it's a sure sign there is water or coolant in it - this will show on the dipstick after the engine has run even for a short time. This poses a serious issue for lubrication and can quickly cause corrosion of the bottom end of the engine (crankshaft and camshaft bearing surfaces, oil pump, valve train) which can cause a catastrophic failure of the bottom end. Avoiding this and any considerable overheating will allow the repair to be still performed without further damage to the engine.