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Disappearing coolant

Then I would just continue to monitor the coolant level, check it every other fill up at a minimum, and track how much you have to add.

This is one of those things that will most likely just slowly get worse--if you watch for it you should catch it in time to prevent any major problems.

Good luck.
 
That much loss has to be going someplace!

Get flashlights and have a good looksee --after dark--.

-Watch for mist, or steam, or small stream from top and bottom of engine compartment (at full operating temperature, engine off). Check all parts of the cooling system, all angles.

Good Luck,
Orange
 
Am I correct in saying a "steam cleaned" plug would be completely spotless compared to the others in the engine? I'm looking at my friend's 2000 4.0 XJ tomorrow. The complaints are: been loosing coolant for a while with no apparent leak points and now rough idle/some loss of power. Interestingly he tripped a P0303: multiple engine misfire cyl #3. I'm guessing cracked head and the coolant is going down cyl 3. Would a compression test show lower compression on #3 with the crack in the cyl head? Also it sounds like I might be able to see a crack through the oil filler cap without pulling the VC, correct?
 
1987Comanche said:
Am I correct in saying a "steam cleaned" plug would be completely spotless compared to the others in the engine? I'm looking at my friend's 2000 4.0 XJ tomorrow. The complaints are: been loosing coolant for a while with no apparent leak points and now rough idle/some loss of power. Interestingly he tripped a P0303: multiple engine misfire cyl #3. I'm guessing cracked head and the coolant is going down cyl 3. Would a compression test show lower compression on #3 with the crack in the cyl head? Also it sounds like I might be able to see a crack through the oil filler cap without pulling the VC, correct?
Click to expand...

Correct, if a plug is getting "steamed" it will be different, and very apparent.

2000 4.0 sounds like the infamous 3/4 crack, not sure if you can see it without removing the VC though. Compression will tell quite handily, or you can crank it over with the plugs out and depending on how bad you will pump out coolant--messy but fun to watch.
 
I think I'll pull my plugs too and take a look. However, there's no apparent loss in power....runs great!

Back to the mayo business. I am getting a little on the filler cap. Is this a definite sign of water in the oil? So many places for this stuff to show up. I don't mind fixing it, I just want to know what the problem is. Will learn more tomorrow. May have to crawl under with a flashlight as one of you guys suggested, but if it's from a hose or radiator or heater coil or something, why the mayo?
 
Mayo is a sign of moisture in the oil--the big question is where did it come from. The crankcase is always going to have moisture from the atmosphere in it. Lots of cold start and short trips--less than 20 minutes in duration--and the engine never heats up to the point that the moisture in the oil/crankcase can get cleaned out. Depending on the local humidity the amount of atmospheric moisture in the crankcase can vary.
 
My 2000 is the same way. Assumed cracked head. The coolant has to be going somewhere! Mayo on the cap. Uses at least a half a bottle of coolant in less than 1000 miles. Good thing it's my third vehicle! Don't drive it much at all. (If I get up off my ass and change out the head, I can use it like I bought it for.) Never had any sign of coolant in the oil itself. So I have studied this deeply for a long time.

The long term warning is of catastrophic damage to the engine bearings from being exposed to coolant.

If you want to be diligent and take better care of your XJ than I have of mine, pull the valve cover and take a closer look between the #3 & #4 cylinders.

Yes, if you have a LITTLE mayo after a lot of cold stop and go trips, it could be normal, but if you always get it and even get it after a fresh oil change, that is not normal.
 
orange said:
That much loss has to be going someplace!

Get flashlights and have a good looksee --after dark--.

-Watch for mist, or steam, or small stream from top and bottom of engine compartment (at full operating temperature, engine off). Check all parts of the cooling system, all angles.

Good Luck,
Orange
Click to expand...
OK...did that. No leaks! Can't find a drop. Will now let it cool and see if mayo has formed on underside of new oil filler cap.
 
I looked at the 2000 4.0 this afternoon and the #3 plug was cleaner than the others but I wouldn't call it spotless. I pulled the Autolites (which looked surprisingly bad after 6K miles) and put in Champion double platinum plugs. The #4 plug actually had deposits that connected the electrode and ground, which would explain the misfire. It wouldn't however, explain why the computer registered it as cyl #3. I told him to drive it for now and see what happens.
Also I pulled the oil filler cap and there's a lot of gunk inside (not milkshake, just black caked on garbage from lack of oil changes). The valve spring just to the right of the filler cap (it would be #3, not sure if intake or exhaust) looked surprisingly clean. Perhaps it's the start of the crack??
 
Bob Hancock said:
OK...did that. No leaks! Can't find a drop. Will now let it cool and see if mayo has formed on underside of new oil filler cap.
Click to expand...
Good long drive today....maybe 75 miles and came home. Let things cool down and took new filler cap off. A very light amount of mayo is there. Oil still looks like oil that needs to be changed (it has 2500 miles on it and I normally change at 3000).

So.....my guess is that I have a minor something going on that is getting enough moisture into the engine to make the mayo. I thought about looking at the plugs but how do you do that? There's all this stuff, what looks like a rail, etc. Not like I could just pull a plug like I do on a bike.
 
There are 4 bolts that hold the coil rail to the head. Remove those. Then you rock the rail aroound a little to loosen the boots on the spark plugs. It's all one unit. If it is holding on too tight, you may need to work the boots individually to get them to free up. It may also come off real easily. You should be able to get the rail out of the way enough to pull the plugs. A little dielectric grease on the boots before re-installing is a good preventive to seal out moisture and aid future removal. Snug the bolts back up evenly. Spec is 250 IN/lbs or about 20 ft/lbs. Not critical, just snug them up evenly.
 
I didn't read every response but i will throw another source for a "mystery coolant leak" out there for you to think about.

There is a freeze plug at the rear of the block and is covered by the aluminum flexplate where it meets the bell housing, it will rot out and leak but the coolant evaporates before it reaches the ground or it mixes with a RMS leak and looks like oil.

When I pulled my 90 RENIX motor out I found the leak that my dad and I had been chasing for close to 10 years. You could smell it but it was invisible. The freeze plug was completely rusted through. The Jeep was less than 7 years old when we started noticing that coolant was going somewhere and having a tight system is a must with the old "closed" systems
 
There were 5 of those along the driver's side of my '88. 2 were rusted through. I just got 5 new brass ones at $3 a piece. Shouldn't need to worry about them again...
 
Another good data point. Thanks.

Right now I think I need to find out why the mayo. Now that I've received a good tutorial on pulling plugs I may do that next. Then take it to the local Jeep guy and see what he says. In the 75 miles it took to generate the slight mayo, the coolant tank lost about a pint. FWIW.
 
I know many will advise against but I had a crack in the head of me F-250SD that was filling up a spark plug well. With 243,000 miles I didnt want to pull a head and get into a bunch of work so I put some stop leak in it. Worked perfect. Truck still runs great. It will buy you some time and costs about $7.
 
There have been multiple posts about a cracked head, this is probably what is going on. It will not show up in your oil, and the engine will pass a block check for combustion gasses in the cooling system. The normal place for the 0331 head to crack is directly between the #3 and #4 cylinders directly on top of the head. Remove the oil cap and use a flashlight to check the head right between #3 and #4 exhaust valve springs(directly below the oil cap hole). If there is cast in letters on the head of some sort in this area then the head is most likely OK, if not check further. The leak will appear as a green/brown crust on the head or even as bright green coolant. If you still can't see it, a bit of coolant dye added to your cooling system and a small UV light will pinpoint the leak.

Continuing to drive your vehicle with coolant in oil, even trace amounts, can ruin your engine bearings.

Seems like you got the correct advice already, you just need to investigate this a bit further.
 
itbrokeagain said:
I know many will advise against but I had a crack in the head of me F-250SD that was filling up a spark plug well. With 243,000 miles I didnt want to pull a head and get into a bunch of work so I put some stop leak in it. Worked perfect. Truck still runs great. It will buy you some time and costs about $7.
Click to expand...

I've heard that they now sell good stop leak that really works. It might be worth a shot.
 
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