Where did my oil go?

2000 XJ 4.0L 98K miles, new Alabama Cylinder head at 84K miles.

So I've had this jeep for about a year and a half, I've owned two other cherokees previous to this one. All of the typical leaky seals were replaced after I bought it. Valve cover, rear main seal, oil pan gasket. This jeep doesn't leak a drop. I have no loss of coolant, or oil going into the coolant.

Oil pressure is 50 idle 60 driving cold, and 15-20 idle and 45-50 driving hot. I've always used Mopar filters. I've used synthetics in the past, and recently changed from Castrol synthetic to Mobil 1 10w30 high mileage synthetic. This jeep has never burned oil before, and was always still full when I changed it at 3K miles. When I put the 6 quarts of mobil 1 in, the oil level was right on the full line, and stayed that way for awhile. I check my oil pretty often, and it was always full. Never had to add any.

I was recently in the hospital, and my dad drove the jeep for a week. 2 weeks after I got out I had been driving it, but wasn't allowed to lift the hood open. Yesterday I checked it, and it was nice and black and about 1/2 - 3/4 of a quart low. Its been in the upper 80s here, but the jeep has only had this oil about 2500 miles. Theres no drips, and it doesn't seem to smoke while its running. No oil in the air filter box either. Oil pressure was still normal, and the jeep ran fine. Any ideas where it went? Just as a test I put in some Rotella 10w30 to see if it changes anything...

wow your worried about 1/2-3/4 of a quart less when the oil is black. i would be concerned that its black and would change it. the oil is not supposed to be black. could be burnt or contaminated.

not saying the oil in my 89 doesnt get black, but thats when i know to change it.

i was always under the impression that oil would burn-off after awhile and thats it is normal for the engine to "use" or "burn-off" oil, so you should suspect less oil after awhile.

It wasn't filthy black on the dipstick, but definitely darker, and not amber. My gas mileage seems the same, so I don't think its running rich. I'm just stumped because normally I can go 3K miles and its still full. The oil looked the same color, but there was less of it. I changed it last night so now I'm definitely going to watch it closer. I'm changing my plugs soon so maybe they will tell something also.

How about 1 qt per 500 miles--that was the SAE "acceptable" oil usage standard back in the mid eighties.

I wouldn't worry about it, just monitor your level. Switching to Rotella is a good idea, however it will turn black very quickly as it cleans the engine inside.

Moble 1 is known for its excessive "burn off" in the LS1 community.. might have have the same effect in 4.0... LS1's are known to "drink" Mobile 1, but not burn oil when other brands are used.

stephenspann27 said:

Moble 1 is known for its excessive "burn off" in the LS1 community.. might have have the same effect in 4.0... LS1's are known to "drink" Mobile 1, but not burn oil when other brands are used.

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This.

3 points to make:

1st.. many XJ owners would be ecstatic to only use 1/2 to 3/4 qts in 2500 miles
2nd.. changed oil brands and now it uses oil... not hard to connect the dots.:laugh3:
3rd.. Oil IS supposed to get black. that means it's doing its job and carrying the dirt as a good detergent should.

Digger87xj said:

3rd.. Oil IS supposed to get black. that means it's doing its job and carrying the dirt as a good detergent should.

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only in an engine that has "dirt" in it. the 4.0 seems to be a bit more dirty then most engines. wifes matrix has 110,000 miles and the oil is a nice amber/yellow color.

the oil build-up/sludge in my 89 was incredible. ive owned my 89 since 1990 and drove it for 10-12 years with just doing the basic maintenance and fixing any problem that arose(a couple of radiators and waterpumps, brakes, exhaust manifold, blah blah blah).

i decided to keep the jeep, so i started an overhaul and lift because the suspension was shot. the engine always had blow by with the usual oil in the air filter with oil leaks everywhere.

i decided to fix all the leaks(rms, valve cover, oil filter adapter) and the blow by. i was amazed at how much sludge there was on the rockers, back side of valve and baffles, and the 1/2" sludge at the bottom of the oil pan. i fixed all the leaks and mechanicaly/chemically cleaned all that i could with the oil pan and valve cover off.

with everything fixed i went with a year long plan/procedure to clean the internals with an engine flush along with seafoam right before each oil change and multiple oil filter and oil changes at sort intervals. also fixing the blow by with new ccv lines/grommets and always making sure the rear line does not get clogged.

long story short, now when i check the oil in my 89(with close to 250k miles), its a nice dark amber color. nothing like it was before.

during the 10-12 years of breaking the xj in, i was never consistent with what oil i used although i remember using castrol gtx quite often along with a fram filter. now i use rotella synthetic if i can find it at walmart, if not i use the regular/conventional rotella t with a napa gold or hastings filter.

I go through a quart every 150-300 miles depending on the phase of the moon... not sure where it's all going, mostly out the RMS I think, but I never have to change my oil, just keep topping it off and replace the filter once in a while. Oil is cleaner now than it was 5 minutes after the first oil change I did when I got it.

stephenspann27 said:

Moble 1 is known for its excessive "burn off" in the LS1 community.. might have have the same effect in 4.0... LS1's are known to "drink" Mobile 1, but not burn oil when other brands are used.

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I have heard this so I questioned if the Mobil 1 might have something to do with it.

Digger87xj said:

This.

3 points to make:

1st.. many XJ owners would be ecstatic to only use 1/2 to 3/4 qts in 2500 miles
2nd.. changed oil brands and now it uses oil... not hard to connect the dots.:laugh3:
3rd.. Oil IS supposed to get black. that means it's doing its job and carrying the dirt as a good detergent should.

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haha very true. But this jeep only has 98K miles and no leaks. My 90 XJ had 177K along with a RMS leak so I expected to add some oil every now and then. I just thought it was wierd because the oil didn't go down slowly, its like I didn't check it for 3 weeks and suddenly its low. Its also been hot out here lately, and the jeeps been running about 215-218*. I'm monitoring the oil level more closely and hopefully throwing in a 3 row radiator to get the temps under control. Maybe the Mobil 1 just couldn't handle the 4.0L haha.

Boy, and here I was pissing and moaning about a quart every 5000mi when I do the oil change. Mobil-1 oil/filter too. Going to 'synch' all 4 jeeps this weekend too. Tired of keeping track of them even with writing the mileage down on the black mobil-1 filters with a silver magic marker.

Jeepkid - I'm in the same boat. 1992 XJ, 4.0 AW4, NP-242, no mods other than recent tune-up, etc... I used Valvoline Maxlife for all my vehicles, but for some reason all of the parts stores around here have stopped carrying it. I decided to go with what many sites and folks think is the best, Mobil 1 Synthetic. Same deal, oil got dark very quickly, and would trickle down the stick each time I checked it. I broke down and threw in some Lucas oil treatment (and before folks here jump down my throat, it's worked for me very nicely in the past, thank you), and the oil leak stopped.

I've read that if you have a leak, switching to synthetics can make the leak seem worse (something about synthetic oils creeping? Beats the heck out of me...) but my 92 didn't leak oil at all. There's no blue smoke out of the tail-pipe, the air filter is the same as before, there's no drips or puddles under the Jeep... It's like the Bermuda triangle of engines!

Ah well. I did pick up nearly a half-a-mile per gallon in economy, at least that's something...

other then just being black from cleaning the engine(high detergent), black oil is also an indication that it is burnt. i would be surprised as i thought synthetics could handle more heat then conventional oils.

maybe m1 has a low threshold for heat?:dunno:

XJPhoenix said:

Ah well. I did pick up nearly a half-a-mile per gallon in economy, at least that's something...

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how's your oil mileage :anon:

People have started joking that I should charge oil money to deliver parts rather than gas money.

XJPhoenix said:

Jeepkid - I'm in the same boat. 1992 XJ, 4.0 AW4, NP-242, no mods other than recent tune-up, etc... I used Valvoline Maxlife for all my vehicles, but for some reason all of the parts stores around here have stopped carrying it. I decided to go with what many sites and folks think is the best, Mobil 1 Synthetic. Same deal, oil got dark very quickly, and would trickle down the stick each time I checked it. I broke down and threw in some Lucas oil treatment (and before folks here jump down my throat, it's worked for me very nicely in the past, thank you), and the oil leak stopped.

I've read that if you have a leak, switching to synthetics can make the leak seem worse (something about synthetic oils creeping? Beats the heck out of me...) but my 92 didn't leak oil at all. There's no blue smoke out of the tail-pipe, the air filter is the same as before, there's no drips or puddles under the Jeep... It's like the Bermuda triangle of engines!

Ah well. I did pick up nearly a half-a-mile per gallon in economy, at least that's something...

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I've heard others say synthetics can make the jeep leak more. The problem is that all my typical leaky gaskets were replaced shortly after I bought the jeep. I park it in the garage and theres no drips whatsoever. I've even looked under it after running it for a bit and nothing seems to be leaking. Like said above maybe M1 doesn't have a very high heat threshold. It was fine for the majority of the time it was in there, but then towards the end of the change interval it went down... The oil wasn't filthy black either. It was definitely dark, but I could still read the dipstick. I'm trying Rotella and seeing what happens.

kastein said:

how's your oil mileage :anon:

People have started joking that I should charge oil money to deliver parts rather than gas money.

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*L*

Same here, except its lifts for friends with no car.

jeepkid03 said:

I've heard others say synthetics can make the jeep leak more. The problem is that all my typical leaky gaskets were replaced shortly after I bought the jeep. I park it in the garage and theres no drips whatsoever. I've even looked under it after running it for a bit and nothing seems to be leaking. Like said above maybe M1 doesn't have a very high heat threshold. It was fine for the majority of the time it was in there, but then towards the end of the change interval it went down... The oil wasn't filthy black either. It was definitely dark, but I could still read the dipstick. I'm trying Rotella and seeing what happens.

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I'm wondering if the reason the oil turns dark faster is due to a different type /higher level of 'anti-sludge' stuff...?

XJPhoenix said:

*L*

Same here, except its lifts for friends with no car.





I'm wondering if the reason the oil turns dark faster is due to a different type /higher level of 'anti-sludge' stuff...?

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Usually it is from not getting the oil hot enough to cook off the moisture, short hops will do it.

Mobil one is your problem...It is crap...Stick with Rotella and you wont have any issues...

Have you tried looking in the gulf? I think some people lost their oil there.

91XJBUBBA said:

Mobil one is your problem...It is crap...Stick with Rotella and you wont have any issues...

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I'm running Rotella 15-40w but.. I bet its not great for mpg.. No leaks and very little burn off though.. even at 270k miles..

stephenspann27 said:

I'm running Rotella 15-40w but.. I bet its not great for mpg.. No leaks and very little burn off though.. even at 270k miles..

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I'm running their T5, which is 10w30 heavy duty. :thumbup: