non f-body; weird heating up

[quantum]

Sorry to post something that doesn't apply to my bird; but I'm out of ideas and could really use some help. With that said here is my problem and what I've done so far.

The problem is that for the last few months my jeep cherokee 4.0 has occasionally been heating up faster than it ever has. It's never overheated (the electric fan stops that), but it heats up much faster than normal. It's not constant; happening everyonce in a while; and I don't know what causes it to start ether.

So far in order to solve this problem I have replaced the coolant (many times in the course of these possible solutions), replaced most of the hoses and checked them all, replaced the water pump, replaced the radiator cap, replaced the thermostat, replaced the radiator (I put in a heavy duity so it's a bit cooler, but still not the same), and replaced the heater valve (little vacume driven plastic thing). I've checked for a blowen head gasket (pressure check), but it was fine.

The only things I can think of that I had done just before it started is to have my throtle body serviced, but that shouldn't cause any thing. Also I've noticed that the exaust smells different, hotter or something. I like my jeep and I want to see it hit 200000 miles. Does anyone have any ideas? and thanks in advance for your help.

[Al 96 Ram Air T/A]

Maybe..

I'll take a stab at it. Assuming you've exhausted the cooling system as causing the problem, it may be a mixture problem. You stated that the throttle body was fiddled with. It may be that you are now running excessively lean. This condition can cause very hot exhaust gas conditions, which will cause a cooling system to work overtime. If the conditon was ignored long enough, you may have chocked your catalytic converter, which in turn will raise the exhaust temps. further. My thinking is that you've stated the exhaust smells funny (rotten egg or acrid ?). This is a prime example of a burnt converter. You'll need to first change the converter and then adjust the mixture. Leaving it lean can burn a piston real fast. Your plugs may be shot as well if the lean condition was left long enough. Pull a plug and check it's condition. If you can, remove the cat. and check the inards. It may appear melted if it got hot enough, restricting air flow.

[quantum]

I was thinking something similar. The only reasion I think it isn't that is that if it's that lean it should trip a light or at leat I think it should. It's a computer contoled engine so if it's lean should'nt it cause a error? I'll check it out though. Thanks for the suggestion, I'm glad I wasn't the only one who thought it may be the cat. Here is a stupid question. If it is damage caused by the throtle body work the dealership did and I can prove it, do they have to fix every thing it caused or just the throtle body?

[Al 96 Ram Air T/A]

Odds are, the dealership will deny any wrong doing. I'm not sure what year the Jeep is, but if it may not trip a "light" , especially if it's pre 1996 (OBD-2). The car will attempt to compensate, until the O2 sensors burn up. Now that I think of it, the O2 sensors should be replaced. You failed to tell me how many miles or the year on the car...

[Jeff_in_Atl]

I had a similar problem with my last Mustang. I did a compression check and it was fine. It failed the NAPA blown head gasket test. It either had a bad head gasket or a cracked head. It was blowing air into the cooling system which makes the cooling system not work well.

I don't think it is the throttle body. The computer should compensate for a little error in it if it is not too far out of range.

BTW I denied my Mustang problem was a cracked head for 10 years before I did the head gasket test which it failed which is the reason I drive a Z now.

Oh and I was not getting oil in the water or water in the oil or either in the cylinder.

[quantum]

Sorry, the jeep is a 94 with 173,500 miles. I did a check on the pressure of the cooling system while the engine was running. The pressuer was perfect, and the needle didn't vibrate a bit. As for the O2 sensor I replaced it at 120000, I suppose I could do it again. Thanks again for all the help.

[Jeff_in_Atl]

I had mine pressure checked at a radiator shop and it passed. The cylinder pressure is way higher than what they pressure test it at. I denied it for 10 years until I got the NAPA head gasket test kit. It failed it big time. The sounds very similar to what I went through. I put a Griffen radiator 2" aluminum radiator on it along with 3 yes 3 electric fans on it. I had a 2800 CFM Black majic fan along with 2 1350 CFM fans beside it and it still overheated.