2000 GC laredo Overheating

[Scott1975]

About a month or so ago, my 2000 Jeep GC laredo with 4.0 straight 6 overheated due to a bad fan relay switch. I replaced the switch, the fans started working again. When it overheated, I had coolant boiling out of the overflow tank and radiator cap. It had hit 260degrees. So I shut it off as soon as I seen the check guage light come on. When I replaced the relay switch, I went ahead and replaced the thermostat, flushed and reversed flushed the radiator. checked the fins on the water pump, they are plastic, so they are ok. pressure tested the system, no leaks found. changed the oil, oil looked fine. Now here is the problem, when at idle or driving with A/C on, the temp will go up to around 235-245 pretty fast. I have to turn off the A/C, turn on the heat full blast,put it in neutral and rev to around 2000rpm for it to come back down. With the A/C off and going down the road, it will heat up, but not as fast as with the A/C on. I did a compression check on the system, found 135psi #1, 155-160psi #2, and 180psi #3-6. I always thought that they are supposed to be within 20psi within each other.I put my coolant funnel on the radiator to check and see if have air in the system, when I release the throttle, bubbles will come back up,but I made sure there was no air trapped in the system. Do I have a cracked head gasket? cracked head? this is starting to kill me, everything was fine before it overheated.I cant figure it out. any help is appreciated.

[jtschwab]

We had the same problems. We replaced the switch and all. We would turn on the heat to get the car to cool down as well and we could never drive through town with the A/C on because it wouldn't take long to over heat. We checked into possible recalls and we had the "Electric Radiator Fan" and "Intake Debris Sheild" replaced per recall bucks. It fixed the problem. I wish you the best.

[Scott1975]

Ok I will check into the electric fan and shield. Another thing I noticed is I am getting some crapy gas mileage. Ever since it overheated, my mpg has went from 19 to around 15mpg. Might be the cat, its about time for it to go bad with 80,000miles. I would just hate to start tearing into the head gasket to find out it is something else. thanks for the input.

[Bob D.]

The "Intake Debris Shield" is a NHTSA recall, where the 4.0 liter engine design could allow debris to accumulate at the #3 cylinder and cause an engine fire.
A manifold shield is installed to prevent this but the lack of it should not affect cooling.

The electric fan is another safety recall where the fan blade/s could separate from the fan hub and penetrate the fan shroud causing injury.
If you hear a droning sound and have a vibration at idle it's possible one of the blades are cracked, it will eventually separate from the hub.

Go to the jeep web site- http://www.jeep.com/owners and plug in your VIN # to find the status of the recalls.
I doubt either is the cause of your overheating problem though.

Have you checked the electric fan for proper operation? It's two speed. With the a/c off, it should turn on low at approx. 210* and high speed right above 210*. When the a/c is switched on it should also switch to high speed.

When it overheated it should have gone into "limp mode"
But if it hit 260* there's a good chance of a cracked or warped head, blown gasket, cracked block etc.

A 180 psi compression reading is high.

[Scott1975]

What makes the the fan a 2 speed fan? Sounds like its just a 1 speed fan. Does the fan relay switch make it switch speeds, or does the fan motor switch the speeds? I checked for the recalls, my jeep is ok with those.

[Bob D.]

The PCM monitors temperature and tells the relay what speed to run the fan at.
If it doesn't switch to high speed it's almost always the relay and the engine will overheat.

You can tell if the fan is changing speed by listening as the engine heats up - the fan becomes very audible when it goes into high speed mode.
To make sure you can hear it open the hood and idle the engine until the temp. goes over 210. Leave the a/c off so you can note the change. It will either switch to high around 212* and keep it in the 210-212 range or continue to rise if it does not.
This is assuming the engine is ok mechanically, if the engine or cooling system is damaged, nothing may keep it from overheating.

Bubbles in the radiator are not good, was that a one time occurrence or any time you check it?

[Scott1975]

I never did notice bubbles in the radiator before it ever overheated, only after when I had did my repair and flushed the system. at idle, there was no bubbles, but when I held the motor at around 1500-2000rpm and let off, the bubbles would come up. I thought I might had air in the system, so I used my funnel on the radiator neck to air the system out with the heater on. Plenty of hot air came out during idle. I will have to check the fans again, I do know they come on high when the A/C is on. thanks for the info.