Engine: Inline 6 4.0

Issue: started like this, every 250 miles driven my coolant sensor would go off "low coolant". Check reservoir and surely it was down to the "add" line. That would constantly happen every 250 miles for about five times. Then got worse, down to 165 miles for about three times. Then worse Nd worse, and now every 45 miles it's down to add line.
Radiator has been replaced, along with electric fan. Pressurized system, checked all hoses, put it on a lift, checked under neath, above, checked oil, trans fluid. smelt exhaust (no coolant smell) it has never left puddle or visual signs of leaks. Never overheated, not coming out of overflow tube.
I can NOT find where the coolant is going, the radiator stays filled up when you check the cap. But it is vanishing and the sensor is annoying me.

WHERE IS THE COOLANT GOING?

 

This interests me because my 2000 WJ is doing the same thing, however my add coolant cycle is about 750 miles. Same troubleshooting results. No power loss, no overheating, no visible sign of leakage. I have noticed after long periods of idling, a few drips of water out of the tailpipe. No smell, no taste (yes, I've tasted it), I've even caught some on white paper. It's clear.

The heater works perfectly, no smell, no wet carpets, nothing unusual. It's worrysome because it could be a precursor of something major. I pray it's not.

I was thinking it could be evaporation because the snap cap on the reservoir isn't tight. Your add cycle makes me think it's not. I'll keep researching and keep you informed about what I find.

 

I would love to know what it is, so when/if you find out, I'll be waiting.

I thought I would add this information as well.
The coolant in my radiator is green (suppose to be) which is what was put in it when the radiator was changed out about 1,000+ miles Ago.
So I change things up, I switched to orange coolant (for gm vehicles) just to see if it was going to the radiator then leaking some where. Well it's not... Coolant is still solid green in the radiator but I keep filling the reservoir up with orange, and it jeeps going somewhere. So where ever the coolant is going, it's getting there before it gets to the radiator.

Also what I started to do yesterday is not fill it back up. So my sensor is still alerting me I have no coolant, which it's sitting at the add line. And I'm driving it daily just to see if the jeep overheats, so far nothing I have drove it 30 miles and it's staying just under 210 temp.

 

Year 2000=0331 head defect=mysterious coolant loss.
Also year 2000 have a reputation for leaky head gaskets.
You can buy 2 stop leak pellets from any GM dealer and try that for a diagnostic aid....if it stops the loss or slows it down it could be head gasket, if it doesn't it could be a cracked head. DO NOT USE MORE THAN 2 PELLETS!!

 

You used Dexcool? Seriously? Not a good idea. Dexcool is propylene glycol. The green coolant is ethylene glycol. They really don't mix. A mixture will tend to gel. Use either, but don't mix. Dexcool was designed for aluminum radiators to reduce corrosion of the aluminum.

As near as I can find, Jeep switched to Dexcool in 2001. I wanted to know because my 2000 had green in it when I bought it.

Your not talking about the yellow (Asian) coolant, are you?

 

I thought head gasket too, but no mix in oil or smell out the pipe.
And yeah I considered the gel when mixing but I did it for testing.
Still haven't found the cause

 

It sounds to me like a cracked head. From what I've read, most folks with a cracked head never see any real symptoms other than the unexplained coolant loss.

 

Cracks in the valve passages usually don't show up as overheating or leakage into the oil. They also can be difficult to find. The only real way I know is to clean the head, sandblast it, then Magnaflux it. I suppose you could take both manifolds off and high pressure test the water jacket, watching for leakage in the ports.

If you're loosing a substantial amount of coolant over a short time, I would suggest it'll show up in the exhaust. You should be getting a lot of steam even after it's fully warmed.

Personally, I'm not ready to do anything about mine until it gets substantially worse. I just fill it up until it's about 3/4" from overflowing when cold. Then I get about 750 miles before needing more. Works for me.

 

Any sludge on the bottom of the oil filler cap? If you stick your finger inside the valve cover and dig around is there a good bit of sludge? When I was shopping for a Cherokee I ran into this more than once on 2000-2001 models. I could only assume a suspicious head and walked away even though they ran great and had no other obvious problems.

 

They often don't have other symptoms... Butttt I did test drive one no issues, no sludge no nothing... I knew what I was looking for ( or so I thought) I bought the jeep for 1k and started driving her home, got 2 miles and the temp skyrocketed pinned it and I pulled over and had it towed back to the dude and got my money back.

It didn't want to overheat until I ran it for a lil in higher Rpms I even let it run while checking it out for 20 mins no issues, no issues driving it down the street either. Coolant looked good, it didn't have a bunch of new cooling related parts either. So you really have to be careful

 

You see, that's the thing with mine. It has never even showed signs of overheating. The temp guage only ever varies one needle width above or below the center mark. EVER! I've even on one occasion sat idling for about an hour with the A/C on.

 

Yes it happens like that often. Like I think someone already mentioned the type of crack that happens with these between the 3/4 cyls usually doesn't make the motor overheat. But mysterious loss of coolant is always a bad sign. If you want, you can take your valve cover off and take a look. But you'll need a sharp eye to catch it if it's small. You might take it off and see a clean line through everything else which would be covered in oil... Dead giveaway

 

Yeah absolutely never have any over heating issues, but it's looking more and more like a head crack. My bad fortune though due to me just selling my truck and now it's my DD so I can't sit it in the garage and take it apart unfortunately. Guess ill drive it til it blows and let insurance cover it

 

When I due make the discovery of what it is, I will update everyone

 

Thanks! I, for one, would like to know.