2000 laredo overheating

I have a 2000 Jeep Laredo w/ 4.0 straight 6cly with 80,000miles. I was parked in a parking lot at night, probally around 80 degrees outside temp. All of a sudden my check guages light comes on. I start looking around to see what was going on. I see that the Temp guage is pegged. So I turned the jeep off, then steam started coming out, I opened the hood, Water was shooting out of the radiator cap, and bubbling over in the resevoir. I had it towed back to my house. I started it up, ran fine, noticed the fans werent coming on. Checked the fan, fan was ok, found out it needed a relay. Replaced it, fan works. I checked the thermostat, water pump, and radiator also. I replaced the thermostat, and checked the fins on the pump, the fins are plastic, so they were ok, and it was pumping. Cleaned out the radiator, flushed the system. Tried running it, still heats up to around 240 degrees with the A/C on and at idle, but when I start driving, it will come down to 210. With the A/C off, it heats up, but not as fast. I think I may have blown a head gasket, So I checked the oil, oil looks good, nothing coming out the exhaust. Performed a compression check, #1cyl is 135, #2 cyl is 160, the rest were at 180 psi. checked the plugs, no coolant in the holes, little bit of deposits on #1 and #2 plugs. So I am thinking I have a blown head gasket. Without taking the head off and spending so much time on this, does anyone else think this is what is going on to? I dont know of any other tests to perform. Thanks in advance

you may have a clogged up radiator. but if you still think it's the head gasket look at your exhaust. if there's a lot of steam coming out or smells like antifreeze then the head gasket may have went but these motors aren't too prone to loosing head gaskets. whatever you do make sure you change your oil and soon. once it gets that hot it's useless.

I checked the radiator, ran water through it, and it flowed fine. checked the tail pipe, nothing coming out. I wonder if the cat would burn that off before if gets out the exhaust. There is only 2 things I can think of, the water pump or cracked head gasket. I cant see how the water pump can go bad with the hard plastic fins. If I just knew of a way to be positive its the head gasket, because I do not feel like pulling that head in this heat.

Water flowing through the radiator may be giving the impression it's working but ineffecient cooling would suggest that radiator is compromised in some way. It could be half clogged, you can't really see in there. You could just be seeing the flow from the half that isn't clogged.

Make sure your electric fan switches to HIGH when the temp goes over 210*.
Low will keep it at 210*, but when not moving or with the a/c on it needs to increase rpm. Both the PCM and the relay are involved in the fan speed control.
That sounds like what caused the initial over heating.
By the way, a compression ratio of 180 psi is way too high - should be around 130-150 psi.

I had this same problem with my 98 Jeep Grand Cherokee 5.9Limited. It would overheat when I would idle with the A/C on for a long period of time (20 minutes or so), I replaced the radiator and hoses about 2 months after I got the jeep because the radiator had a slight leak. Then I replaced the Water Pump and T-Stat because of the Overheating when using the A/C and it didn't work.

I finally found the problem, the last owner must have replaced the electric fan, well they used a curved bladed (directional) fan, which was fine but when you hooked the fan up (positive to + and Negative to -) the fan pushed instead of pull, well this is fine because I know that if you reverse the polarity or the fan it will change directions, which is what the old owner did fine the fan pulled air just fine, but becasue it was a directional fan it was not as efficient at pulling as it is at pushing, so it was not pulling enough air to keep the engine from overheating while idling. So I had another fan lying around from an old cavalier that I had and hooked it up and now my jeep sits at about 195-200 all the time with the A/C On.

I also had a problem with my expansion valve int he A/C system which caused really high pressure in the system which also helped a lil with the overheating, When at normal operating temp and you stop and sit for a few minutes (maybe 20 minutes) the temp guage would slowly go up to about 235-240 then after a couple more minutes just jump from 240 to 265 (pegged). And after I replaced the expansion valve, the jeep would get up to about 235 but it didn't do it as fast, then I replaced the fan and it is fine now.

Bob D. Had a point I think you problem lies in the fan itself, yours may not be switching to high when the temp goes up. Also check for blockage in the fins of the radiator and the condensor.

Ok, now that I think of it, I had the fan replaced in 05 because I was in a wreck. The question is, did they put the correct fan back in? I replaced the fan relay, but I didnt think it had to speeds. I might try to find me a fan somewhere. Thanks for all the input.

I went and checked to see if all the air was out of the system. Put a funnel on the radiator, filled with coolant, checked for bubbles, not many came out during idle, but when I let off the gas, some big bubbles came out. I dont know if air was in the system, or if the head gasket is sucking air in. I have always been told if the gasket is cracked, there will be coolant in the oil, but there is none. Also there should be some white smoke, but nothing there either. I checked the fan, I guess its running ok, I didnt notice any speed changes. Just one constant speed. Its pulling air through the radiator because I feel the hot air on blowing on the engine side. I dont know if its pulling enough air though. This is killing me, I cant figure it out.