overheating at idle

alright, I have a 94 xj with a 4.0L/5spd. 132K on the odo. I have been having some trouble with it getting to the 240-250 degree range when it's not moving.

I replaced the waterpump with an AZ unit(yeah, i know) about 25K miles ago.

When the radiator started to leak this past winter, I replaced it with a supposed modine from napa(it fit kind of crappy and the box said GDI somewhere in smaller print). it had run a little warmer this spring when it started to warm up, but now it's getting bad.

I threw a 160 degree t-stat in there to try and band-aid the problem for now, but since my problem is overheating at idle, this doesn't work too well.

I had been running just straight water in it like a dumbass, so there was a lot of sludge, even after a couple of good flushes, it's still looking pretty rusty and nasty.

just replaced the fan clutch today to no avail with a napa clutch(which out of the box seemed to spin pretty freely, at least a lot more freely than the stock one.) however on my oem clutch the little thermal coil was pretty gunked up, so that may have been the problem with it. it still has no problem getting to 240-250 degrees while idling. this i'm sure will perpetuate my oil burning problem. so it's no good.

I really just want to rip out all the replacement cooling parts and start again with the high dollar stuff, but if there is any way to salvage the current cooling system, i'd like to try. I definitely want to know the best way to flush all this nasty coolant out of the radiator and motor(maybe using a steam cleaner somehow. any suggestions are welcome and I apologize for the lengthy post.

P.S. other than this problem, the motor seems to run well and it will pull about 13-14 mpg with a 4.5inch lift and 33's on stock gearing(4.56's in the form of an 8.8 are in the works this summer

Do a search for this subject, as it is well documented. If not here then in the modified section. Not being rude, just alot of posts with alot of information.

If it gets that hot, is the secondary electric fan coming on?

I had a similar problem, and still sort of do. Raising the rear of the with aluminum spacers, an inch thick and adding a switch for the secondary fan will help.

I replaced all the cooling system components and flushed the system myself. I also had a shop keep the XJ for 18 hours of tests, flushing, and parts swaps to no avail. They were slow and only charged me for a couple of hours time.

OK, here's another freebie...

It's probably your fan clutch - they're only good for 3-4 years in the XJ. Once you get up to speed, I'm sure your temperature drops, and that's because you're getting more ram air over the radiator, and while you're idling, the clutch fan is slipping too much and you're not getting air over the radiator anymore.

"Fixing" the problem by using a 160* thermostat just won't fly - that just means that the thermostat opens earlier, and you're getting coolant flow (but it doesn't do anything for ram air over the radiator.)

I have a habit of signing and dating the fan clutch when I install it - if an overhead comes up, I start checking dates on parts (I also date and initial the thermostat housing when I change the thermostat, just to keep track of it. I'm funny that way...

5-90

Overheat in traffic or idle, bad fan clutch IF it returns to normal once you get moving at speed. Overheat at speed, plugged rad or bad vanes on the water pump.
Anecdotal, if the fan roars at cold start [first start of the day] for 30 seconds or so and then quiets down the clutch is probably good, thats the hydraulic fluid in the clutch being redistrubuted. If it just stays quiet then it's probably bad.
As for flushing, I'd start with a prestone back flush kit that goes in the heater line, drain whats in there, add water and prestone or zerez 8 hour flush, then back flush the heck out of it, some recommend vinegar, never tried it though it does do a good job on my showerheads and toenail fungus

When you refill use DISTILLED water and coolant, not tap water. Also does your lower rad hose have the spring in it ?
When you tighten the fan belt are you doing it by feel or using a $12 krikit II tension gauge available at NAPA ?
Your 'best guess' at 160lbs for a used belt is probably closer to 80-90lbs.

Ditto. Overheating at idle or in traffic, and then cooling off when you get moving well, is the text-book symptom a bad fan clutch!

well thanks for all of the replys, what do you guys think of this napa clutch i have then? will it stiffen up somehow over time/heat cycling or should I just take it back to napa?

CleanInstall said:

well thanks for all of the replys, what do you guys think of this napa clutch i have then? will it stiffen up somehow over time/heat cycling or should I just take it back to napa?

Click to expand...

If your clutch was shot, the new one should have a lot more resistance than the stock one. I'd take it back to NAPA and have them give you another one.

Also, check the fan shroud, if that's broken, replace it. Could very well be your problem. Check for proper electric fan operation as well.

if you want to flush it cooling sys more use cascade dish washer soap
drain the sys fill a gall jug half wat w/ hot water add about a half cup or so of cascade and shake it till its dissolved then put it in the rad top off w/ water and run at operating temp for 5 min rinse and repete till clean

ive found this works better than over the counter flushes

It could be your radiator cap; it was in my case.

My cap looked brand new, but I found that it had a small leak when I tested it using a Coolant Pressure Tester from Autozone (Loan-A-Tool program) (http://tinyurl.com/fozjt).

The radiator cap is designed to pressurize the system with up to 13 pounds of pressure. For every pound of pressure, the boiling point of water goes up by 3 degrees Farenheit. So with 13 pounds of pressure, water in the radiator will not boil until 251 degrees Farenheit.

If you have a leak in your radiator cap, the water will boil at 212 degrees and turn to steam, instead of at 251 degrees Farenheit.

well I did another flush, and I returned the napa clutch and cleaned all the grime off of the ac delco unit that was on there. after this I haven't had any trouble with it and it's been running pretty cool, even idling, so hopefully i've taken care of the prob. I'm gonna switch back to a 195 deg. t-stat and see if I'm in the clear, thanks again for all the great replies everyone.

-Mike

XJ4PLAY said:

I had a similar problem, and still sort of do. Raising the rear of the with aluminum spacers

Click to expand...

Raising the rear of what? Radiator?

Harlee&Tahoe said:

Raising the rear of what? Radiator?

Click to expand...

Hood maybe? I've heard it can help with overheating problems... :repair:

Know the feeling. Just went through that problem today while finding my electric fan was'nt working. Pulled the cube relay and jumperd the fan to get it to run, Bad temp switch I guess cause fan works. Changed out the 'stat in Oreily's parking lot and filled her up with coolant. Seems to have fixed for now till I get a new switch. Boy she got hot though couple of times. Hope I did'nt hurt anything. Those little 4.0's are TOUGH!

The waterpump was reverse rotation, right? If not, it will be hot at idle, then cool as you rev it. Add a bottle of Redline Water wetter and temps will drop a chunk too!