hi, we have a 2004 grand Cherokee Laredo 4.0L that keeps overheating. I have replaced the water pump, thermostat, electric cooling fan, both hi and low relays, temp sensor, hoses, and fuses are good and still the engine heats up to 260+ goes into the red and blows coolant. this model does not have an electric fan control module. we learned the relays replaced that. Can anyone suggest a solution?

 

Did you put the thermostat in the right direction? You sure the radiator isn't clogged?

 

pull the thermostat out and observe.

Pull off upper hose from radiator and see if water comes from engine or radiator side(confirming correct impeller rotation).

 

When you check waterflow, do it cranking and pull the ASD relay so it doesn't fire up! The copper slug on the thermostat goes toward the engine. Also, before you do anything, idle it from cold and make sure the fan is actually coming on at 215*. If it's like my 2000, it won't start at all until it gets to 215* and runs on high until the temp drops to around 195, then drops down to low and runs until you shut the engine off. It will kick to high anytime the temp goes above 215, then cycle to low again. Also, it will run on high continuously as long as the A/C compressor is engaged.

There are 2 different waterpumps for the 4.0, one for the serpentine belt, and one for the older v-belts. They run in opposite directions. The only way to tell the difference is by looking at the impeller and even that is not obvious. You almost have to have both the old pump and the new one side-by-side. It's possible the guy that sold you the pump wasn't paying attention. If you have to buy another pump, do yourself a favor and buy a premium pump with a metal impeller. When worn, a plastic impeller can strike the cylinder barrel and shatter!

 

Thank you for all the help. the thermostat is in the right direction. It has been suggested the system had air and needed to be "burped". I will try that today.

 

Clue to filling a 4.0; Take the gauge sensor out and fill at the radiator until coolant runs out the sensor hole, re-install the sensor, and continue to top off the radiator. This eliminates 90% of the air in the cylinder head. Once the engine gets warm, you should only have to add a quart or 2. Also, make sure the heater hose from the thermostat housing goes to the lower of the heater core pipes. This way the air in the heater will bleed out by itself.