2000 Grand Cherokee 6cyl.

Just started overheating. Upper radiator hose is hard as a rock. Still has heat from the vents. With the heat blowing in the cabin, it does not overheat. New waterpump about 1 yr ago. So I pulled the t-stat out thinking it was getting stuck. Running at idle, the upper hose got very hard like it was gonna blow, temp gauge went to red after about 15 - 20 min, and electric fan never came on. Thinking maybe a blockage in the radiator? After it cools, I gonna disconnect upper hose and start engine to see how much flow the water pump has. No discoloring in the oil from coolant and no oil present in coolant.

Any other ideas?

 

Thermostat, hoses, radiator and check the cooling fan motor. Time for some maintenance on your 15 year old cooling system.

 

hoses in good shape. Removed upper hose from the radiator and started engine to test the water pump.....had a great flow of fluid so water pump is good. Drained radiator and flushed the system, got a lot of crud out of the radiator. Hooked all back up, refilled system with fresh fluid. Still overheats even when sitting in my driveway. Still don't have the fans coming on. Checked the fuse for the fans and its good. Don't have a book but can someone tell me where the sensor is located that activates the fans? Somewhere in the block? What the .........??? Again, no oil in coolant, no coolant in the oil.

 

The sensor is in the thermostat housing.

 

Yes, but the relay that controls it is underneath the passenger's headlight housing. You have to remove the headlight and cut a trap door in the black plastic pan to access it, OR remove the entire grill! It's a 2 speed fan and it should come on low at around 190* and high at 220*. This is a "pulse-modulated" relay controlled by the PCM using input from the temperature gauge.

THE FAN IS YOUR ENTIRE PROBLEM!!!

For now, you can hot-wire the fan to the ignition circuit to be able to drive it. Another stunning engineering concept! Just be glad you don't have the 4.7 with the hydraulic fan!

There is another approach to it. You could remove the electric fan and install the old style viscous clutch driven fan from the ZJ's. You'll need the fan shroud as well.

 

Under the headlight........? what a ******* place to put it. 2 speed fan? not sure I ever heard / saw a slow speed on it.

Thank you for the info. I would have looked forever for it. I will be testing the fan motor tonight and replace the relay. And put the t-stat back in.

 

So purchased a relay on my way home pulled the headlight and cut out some plastic from behind it. Didn't see a 5 pin relay like what they sold me. Only thing close was a square flat box screwed to the fender well with a pig tail commin off it. So I scrapped that idea for a moment and decided to put power to the fan via the harness. Fan not commin on even with direct power. It spins freely by hand. Used a test light and volt meter - getting power thru the fan but not commin on. Gonna get me a new fan motor and try again.

 

That flat box IS the relay. The PCM pulses the fan motor to control it's speed. I wasn't aware it had more than 1 speed either until I figured out what was making a sound like a gyro-horizon on an aircraft spin down when I shut the engine off. It doesn't turn on until it gets hot enough to trigger the high temp limit, but then it runs at a lower speed after it cools down to the normal operating temp. It gets very confusing trying to understand why it does this. I assume it's to get the engine up to operating temp quicker, but I think the engineer who designed it had a brain fart! The theory as to why the relay is mounted where it is was to keep it cooler than the underhood temp and protected from being damaged.

This is underneath the headlight, not behind it. Be careful with that thing behind the light, it may be the airbag sensor. That's where it was on my ZJ. Actually attached to the horn bracket.

 

Had similar problem with mine, it was the fan motor. Also, that is the relay like Dave said. I went through 3 of those before I realized it was the fan motor burning out the relays. Changed the motor and not a problem since. Now if I can just work out this misfire issue ive been fighting lol.

 

Ok. So it's fixed. Fan motor and relay were bad. Can a bad relay cause the motor to burn out or the other way around ? I just don't see both goin out at the same time but not causing the other to fail

 

A bad motor will kill the relay.