XJ cooling system

I have murmured about this on other threads before, but I am working on an XJ for a family friend.

When I took a routine look at it a while back for overheating issues, I found that some doofus had dumped Dexcool in it on top of whatever was in there before, probably some very diluted green stuff.

It had already started to make mud, so I had her come by the house where I disconnected and independently flushed the radiator, heater core, block, and thermostat. I then reconnected things in various ways and flushed it all again until I couldn't find any Dexcool. I left her with plain water with instructions to check back in a couple of weeks.

Sooner than that, it was overheating again. It was all Dexcool-y in there again, so I repeated the big flush and repeated the plain water, two weeks thing.

Sooner than that, it was overheating again. It sprung a leak through the water pump weep hole. I replaced the pump (the old pump had no impeller left. I suspect mixed antifreeze based corrosion accelerated this, but only a little star remained), the thermostat, the radiator cap, the radiator hoses, and flushed the whole thing again. Only plain water was found this time. When done, I threw 50/50 in it, knowing that I was done.

A week later, after excellent performance, it started overheating again.

Why is it still overheating?

The coolant level seems good, there doesn't seem to be any Dexcool left, I think the mechanical fan is working (haven't checked the electrical fan yet), the radiator looks very good. I am flummoxed.

What year is this thing?

Sorry, I forgot the easy stuff - 94, 4.0, auto

It got the cash for clunkers seize treatment and since it's an XJ it just keeping fighting through it refusing to die.

captdownshift wrote: It got the cash for clunkers seize treatment and since it's an XJ it just keeping fighting through it refusing to die.

This thing truly is the /6 for our generation. She ran it out of oil once, she's massively overheated it at least twice. When I first got to it, its oil has nearing a decade old. The transmission fluid was OEM when I got to it. blah blah, the thing is amazing.

Head may very well be warped/cracked from one of the old overheating episodes and only once a week is it driven long enough to produce symptoms again?

Stop making me want to get another one...I keep telling myself the next tow vehicle has to be at least a 1/2 pickup even though it won't be 10% of the fun

I'd do a leak down test before going further just to eliminate any internal issues.

Is the radiator clogged by chance?

I doubt the head is warped. It is driven about the same amount each day, roughly ten miles each way.

atm92484 wrote: I'd do a leak down test before going further just to eliminate any internal issues. Is the radiator clogged by chance?

Water flows easily through the radiator when tested with a hose.

Seems to have plenty of power.

The 4.0s were anvils, but they did have head and head gasket issues, especially if overheated. I would do a chemical test before I threw anything else at it.

When you filled it, did you remove the bypass hose from the thermostat housing? This is the bestest way to prevent trapped air.

DrBoost wrote: When you filled it, did you remove the bypass hose from the thermostat housing? This is the bestest way to prevent trapped air.

I think so.

My 4.0 WJ was overheating due to the electrical fan relay. Symptoms were similar to having no fan - temps dropped quickly when traveling over about 25/35 MPH, and went up quickly when stopped. Unfortunately, visual inspection doesn't work so well because the mechanical fan will spin the electric fan.

4.0's are a bitch to burp air from because of the heater hose routing. You'll see a lot of them with a 'flush tee' in one of the hoses for that reason. Typically the thing will overheat almost immediately, though. If it takes a week I'm going to guess it's leaking coolant somewhere and when it gets low enough it overheats. That points to a head gasket IMHO.

Quick, someone say something other than head gasket

Cracked head?

XJ's have cooling 'systems'?

tuna55 wrote: Quick, someone say something other than head gasket

Rotor bearings.

In all seriousness, what was the weather like outside? The electric cooling fan tends to fail on those and is an easy fix. The stock mechanical fan cannot keep up with the tiny radiator of those things when climbing colorado roads, ask me how I know :P

Seems the electric fan would be the easiest to rule out at least.

Wouldn't a HG issue show in the oil? Are you even losing coolant?

ebonyandivory wrote: Seems the electric fan would be the easiest to rule out at least. Wouldn't a HG issue show in the oil? Are you even losing coolant?

I'll check the fans tonight. Is this an "A/C on, fan on" situation?

Ahh, coolant. I do not believe she is losing coolant. I know that sounds kind of funny. I should just know. But I do not. It has not been on the road long enough without me opening the system to really know. It's not losing it on a massive scale, it's not pouring white smoke out of the tailpipe, there is no bubbling of the coolant and it's not mixing coolant with the oil.

That said, I have had all of those symptoms before (or rather, all of those non symptoms) on a car which turned out to need a head gasket, it just didn't show itself as 'white smoke in the tailpipe' for several weeks afterwards. I don't know of a truly foolproof way to check for headgasket failure.

I will report back with fan findings this evening. Of course, this means yet another tunatruckless night.

"AC on" or engine at 220 degrees is when the fan is supposed to come on. Otherwise it just freewheels.

As others have said, air in the system can cause this.

tuna55 wrote: I don't know of a truly foolproof way to check for headgasket failure.

I do.

Keep in mind it only shows gasses present, not where they come from. When I was a Rover tech it could mean dropped liners depending on what engine you were checking.

Edit: Personally I like This one better. Not because I make more money selling them, it's the one I used as a tech. Not sure if your FLAPS will have one but I'm sure they could order one.

It's the mechanical clutch fan. Rather, the mechanical clutch fan is bad. I'll put it in tonight. How about now?

Dear Jeep, circa 1980 something. GM does this with their fans

for a reason. Look into it.

There is no good way tog et your hand in here

Anyway, it's done. TIme for cleanup and test drive. Thanks for the help guys.