so i need a little help getting things narrowed down. seems like anytime i need something fixed, i end up doing things unnecessarly.. anyway I have a 99 grand 4.0 that has had some cooling issues. i first noticed when i took a road trip that when i was using the a/c things were fine on the highway, but when i hit the city driving with stop and go the temp was rising rapidly. i didn't even notice until the redline was reached and the sound and indicator came on. when not using the a/c it helps, but now it seems when i am moving at least 15 mph everything is fine. when i hit heavy traffic or idleing for a few minutes, the temp starts rising. as soon as i get rolling again it starts to cool back down to 210 again right in the middle. being this is the cooling system there are a number of things that can be wrong such as thermostadt, plugged radiator, hose, heater core, ect. here is what i know. the coolant level is good, and looks bright green still. i have had the jeep for about 9 months now with no prior issues on cooling. what steps should i take or does anyone know what may be wrong?

 

Your fan clutch is in need of replacement.

 

i believe i only have an electric fan. no fan off the water pump that i can see. i think that is only on the v-8. fan is working, and pulling air through the radiator.

 

you want to first off see if your e
fan kicks on.....should be around 218: or turn on ac....if doesnt kick on then run power to fan and see if it works...if the fan does work and it wont cut on i believe there is a relay under passenger headlight causing it to not cut on...

 

fan does kick on at that mark. just for good measure i ran 12 volts to the plug and is working good.

 

idk...might want to do a thermostat

 

that's what i figure i should start with due to the cost. i really don't want to do the radiatior or water pump and find out it's that little guy. im just hoping someone knows.

 

yeah would start there and if you want flush the system while your at it....maybe new fluid...

 

Ok, finally someone else is having the same issue with thier WJ. Ive had my 03 Grand cherokee since may, and in june mine did the same thing after running it a little hard and for a period of time mine acutally overheated and shut itself down. First thing I did was was replace the thermostat, I reccomend a 190 degree failsafe, $15 at autozone, just for good measure, flush the engine coolant when you do the thermostat, odds are its never been done and its the best time to do it. That howver didnt fix my problem either, still goes above 210-220 when idling after a period of driving. I replaced the fan relay as well, whcih as Jomps said is under the pasenger headlight, need to cut an access panel to get to it though, mine was already cut which means it was replaced before, search internet there are pics on where to cut exactly. I purchased a water pump have yet to put it on but got it just in case. The fan actually is supposed to have 2 speeds, the higher of which is supposed to come on when needed, which I dont think mine is coming on at the 2nd speed. If you do anything though get the 190 t-stat, it will take a little longer for the jeep to go above 210 when driving for a longer duration.

 

my xj starting running hot last year whenever it was in idle for a while. im a firefighter and at a call i have to leave my many strobe lights on to block traffic so i leave the jeep running. i noticed it started running hot and almost knocking off so i flushed everything and that didn't help. so i installed a high idle/extended idle switch. it rev's the engine to 1000 rpm's when in park or neutral. i haven't had a problem since... just an idea if you idle for extended periods of time. amazing, quick, very easy mod for xj's. don't know about zj's but i'd look into it...

 

Just curious if any of you experiencing the cooling issue have inspected the radiator to make sure the fins aren't clogged with dead bugs/dirt/road debris that may be hindering air flow over the cooling fins. Might try hosing it out from the engine side to force anything that might be clogging it back out the front.

 

yes i did. thanks though for the thought. i had some so i pressure washed them out. but it wasn't bad.

 

Don't know if any of you got the issue resolved but I was thumbing through some other forums I follow and saw a post that said the 99GC water pumps have a plastic impeller that could possibly come loose from the water pump shaft causing the symptoms you described.

 

my 99 gc 6cylinder has 2 fans, one off the water pump and 1 electric.
Had to replace the clutch on the wp.