Charc

Hi yall new here and im goin nuts! I have a question, my cooling fan is not running and i replaced tstat ans sensor in tstat housing and relay under pass headlight because before i changed relay i tapped on it before i changed it the fan started working but quit,so i figured that was the problem so i changed it, well it didnt fix it! If i provide grd to the blu pink wire on relay fan runs good,so the pcm is not sending grd to relay? Is that becuz pcm is bad or sum other reason?i dont understand why when i tapped the relay the fan started? With the new relay in i can tap it all day long and it wont turn fan on! I guess i need help figuring out where to go now!? Im gettin so frustrated im not thinkin right! Please help anyone

PatHenry

Is the GC the same setup as the XJ? (In other words, is there a mechanical fan clutch and the secondary electric fan?)

Charc

No it only has the one elec fan no mechanical thank u

PatHenry

The first thing with any electrical concern is to clean and tighten all your engine grounds, battery cables etc. Make sure that's done so you're not chasing gremlins.

Next, are you sure that all the wiring is correct and the relay is the correct part number?
Finally, get a copy of the Factory Service Manual for your vehicle. There will be a complete wiring diagram and a wealth of test procedures that are specific to your year GC.

I would suspect a less severe issue (wiring - maybe the PDC grounds/connections..) before swapping out the computer.

If you are having trouble deciphering the diagrams or testing info, ask.
I'm not super knowledgeable with the wiring/electrical, but you might ask Jordan96xj, he's very good with that stuff.

Charc

Thanks,i have checked all grds, and i have a schematic of the fan circuit and its really very simple, i used to be a elec repair so iv read many schematics not bragging just saying i got that down lol and im goin to test the new temp sensor in morn if it warms up a bit just to see, and test draw of the fan motor ? Ill post results soon as i get them thanks again

PatHenry

I don't know about the GC, but on the XJ the aux fan is triggered by the temp switch (on the t-stat housing).
If your temp switch replacement wasn't Mopar or a high quality replacement, it could be bad out of the box. I'd test the wiring on the switch too - see if it's correctly signalling the computer that the temp has reached a certain level.

Charc

Ya thats the tests im doin today,so after i see whats goin on there ill post if i cant find the problem im just goin to hook it to a keyed hot and have it run anytime jeeps running,or maybe put a switch inline im not going to spend too much more time chasing crap.

dave1123

The fan relay is pulse-modulated by the PCM to control speed. An amp overdraw caused by bad bearings can burn it out. The fan motor is a permanent magnet motor and you should be able to feel the magnet poles when turning it by hand. That shows the bearings are free. It think the fan is fused at 40 amps, so there must be quite a draw on it.

the way the system works is the fan won't run on startup until the engine reaches210*, then kicks on high returning to low after the temp drops below 195*. It will run on high again any time the engine gets up to 210*, cycling as before, and continuing to run until you shut off the engine. It also cycles with the A/C.

You asked about parts brands before? I replaced both the fan and relay over a year ago with Dorman. When my relay died, I ran a fused switch directly to the fan from an ignition power source until I could get time to chop a hole in the headlight support to replace it. It ran fine that way for 2 weeks, but always sounded like a vacuum cleaner!

Download your FSM from pacificcoastmanuals.com for $7.99+ tax

Charc

Well i understand how it works, it just wont work lol i did the test to figure draw of fan and its only 32 amps so well within specs of free not going bad? So why does fan not run?i know its gettin over 218 as it bubbles and stea.s and my laser therm shows over 225 so its hot if i grd blue pink trigger wire out of relay fan works? I need help here im goib freakin insane over this! Can i put a mechanical fan on it and say forget the ekec one?

dave1123

If I were you, I'd run both. Install a clutch fan and add a dash switch for the electric one. That way you can turn it on only when you're caught in traffic or something and it gets too hot. If you want to get fancy, install a temp sensor in the upper rad hose and a relay to make it automatic. Guys that do rockcrawling often do that.

HP2

I just picked up a '99 and was a bit surprised to see it had no mechanical fan on it. The previous owner rigged up a switch for the electric fan, so I suppose he had the same issue mentioned above. I thought maybe the oem mechanical fan had failed and was replaced by an electric but evidently not. I was planning on digging the electric out and installing a mechanical unit on the water pump as it has the threaded shaft and appropriate shroud to allow a mechanical unit. Might have to really dig into why the electric failed and how to restore ts function.

Charc

Dont ya think that just having the clutch mech fan like all older vehicles that would be enuf to cool it? It was plenty on the old v8s? I dont see why a inline 6 would need both?

HP2

No doubt it would. I suspect the only reason why the went electric is for marketing purposes and fleet mileage. With no other change, you can increase power output 8-12 hp which always looks good on sales brochures and since it also results in a 2-3 mpg increase, over the fleet that would have saved Chrysler tens of thousands in EPA fees.

Charc

I think ill try it since no one seems to know how to fix my problem? Im at a loss!

dave1123

The main reasons these engines need more cooling control is the operating temperature is higher than normal to control emissions, therefore must be held more closely. Remember older engines normally operated at 180* and could run as high as 220* without problems. When you start 15* higher, 220* can come quickly. The 99-04 4.0 actually have smaller exhaust ports to keep gas velocity higher for better catalytic converter performance, but they strangle the engine's performance. This also increases the flame heat inside the head which is probably the main reason for the 0331 head's tendency to crack. Everybody thinks they made the ports larger creating weak spots, but that's not true. I was under that impression myself. These higher exhaust temperatures were the reason for the cast iron manifolds.

As a whole, the WJ platform was an experiment for the new 4.7 V8. Chrysler knew the 4.0 was reaching it's emissions limitations and needed to be replaced. The public wanted a smoother body style and better performance. Because of the higher EPA standards the 99 4.0 had BOTH a clutchfan and an electric one. In 2000 they eliminated the clutchfan because the electric one worked well enough by itself. In 2001 they tried a hydraulic fan on the 4.7 to reduce the electrical load on the system so they could add more electronic stuff without adding a larger alternator. That became more of a problem than it was worth. They are expensive to replace.

This was also the time when there was an explosion of 4WD and AWD SUVs on the market and jeep was loosing it's market share.

Enough rambling. Your problem isn't easy to fix if the wiring isn't at fault. The fan is controlled entirely by the PCM reading the one-and-only temp sensor on the engine and sending controlling pulses to the relay. If that isn't happening I don't know how to fix it either.