1991Jeep_Man

God, I know this thread will probably explode, but I want to understand what is going on in my 4.0. This thread is regarding oil.

My XJ is a '91 Laredo. 207K miles on the original engine/tranny/t-case/axles. Bought it about 2-3 years ago with like 190K miles. For a long time, I ran 10w30 in it like was listed. First tried Pennzoil Platinum. Didn't like it (seemed to be noisier, and burn more oil). Switched to Mobile 1 10w30. Good to go. Seemed ok.

Recently, I switched to Mobile 1 10w40, and finally my most recent oil change with Rotella T6 5w40. I figured the Xw40 would help with engine wear and oil consumption. I noticed less engine noise at operating temp with the Xw40 oils, and from what I could tell less oil consumption (but I mostly drove around time. Interstate drives were at most 5 miles). Switched to 5w40 for easier cold starting. Noticed less noise at startup. 60 psi on the Oil Pressure gauge at cold idle, then 20-25 psi at hot idle and 40-45 psi at cruising RPM. I figured I was golden.

Recently, I took a trip with some friends to Harrisonburg. About 40 miles to and then 40 miles back. 80 total. Constantly checking the oil (because I am paranoid) and maybe it was just me but it seemed my oil level dropped slightly. But here's the wierd thing. When I did the recent oil change, I filled to the middle of the safe zone, started the truck, ran for maybe 1 minute, then shut off. Wait a sec or two, then refill back to the safe zone. I think I was right at the top line of the safe mark. Well, check the oil the next day, and it seemed like the oil level was suddenly over the mark. Checked it twice. But I never overfilled, and even checked the left over oil and confirmed I had only used about 6 qts. Then I do this drive, and I'm sitting at the top safe line. Is this an XJ joke? Or am I just plain stupid?

Also, what is ya'lls opinion with my oil preference/ reasons for using said oil? Also, I noticed on this trip after going interstate, hot idle was 20 and cruising pressure was 40 psi when slightly past 2k rpm. When I dropped gear to pass someone and hit roughly 4k rpm, pressure seemed to stay still. Maybe 45 psi. Is this ok?

Lastly, I fail to see where I am burning oil. I am not leaking it ANYWHERE (no spots or smoke. All gaskets have been replaced minus the RMS, which has no symptoms of leaking). Yet, if I was burning as much as I had seemed to on an 80 mile drive, you'd think it'd be obvious. You'd smell it, see smoke. But I have none of that. I never smoke at start-up (except for the associated steam with the cold weather). I even put my hand over the tailpipe. Never have any residue land on it. Even under load, I see no smoke. The only thing I smell is my emissions from using a high flow cat. No oil smell though. No puffs of blue smoke. Nothing. What's up here? Do I need to run a 20w50 to solve this mystery issue?

I appreciate any help guys. I know this is a HUGE read, but I wanted to include as much info as possible. Also, don't know if it matters, but I have always run only good brand oil filters. Mopar, Puralator PureOne, Napa Gold is on there now. Wix. Thanks!

SuperGlue

When you let it sit for a while it gives the oil time to drip to the oil pan. Which is why our auto teachers always made us wait =P. I would think that is why it was higher when you checked it again the next day. I wouldnt worry about it. 45 psi is perfect, and in my opinion which oil you use is personal preference and it should be a banned subject on this forum. LOL!

kjc

X2 what superglue said.. On a related note, when I first got my '92 Laredo, well, after I replaced the head gasket and got the head reconditioned and a rms etc etc. I checked all fluids regularly(like weekly) and the oil was always down 1/2 quart after a few hundred miles or so. I kept topping it off whenever it was low, but it just kept 'disappearing' no smoke, no burnt oil lookin' plugs and NO oil leaks anywhere except a little oil film on the hoses for the pvc. Finally, I just quit topping it off and let it sit at a half a quart low. Jeep likee! It stays at the same level between oil changes, and the pvc hoses have a lot less oil on 'em. I can't imagine why this is.. just thot i'd share.

DFlintstone

I might add some zeros to my test run. I'm curious how much blow-by you see power-braking with the oil cap off. I burn a quart in about 1000 miles, and there is no visable smoke. (I had someone I knew was going to be following me watch for it last summer). With a hot idle of 20 and a ceiling below 45 I wonder if someone might mention the relief valve. Anyway I'd bet my "healthy" blow-by, and using a quart in 1000-1200 miles is related.
Also, myself, even smoken hot I would wait more than 1 minute if I wanted to really nail it. Oh and I use ******* *** oil.

1991Jeep_Man

I guess I'm just over thinking it. I mean, my CCV lines are clear (replaced, cleaned the baffle things inside the valve cover, and replaced all the lines). No more oil in the air box. I guess it's just the Jeep doing its thing.

Here's a quick q. When our XJ 4.0's do burn oil, what is usually the cause? Worn rings?

Norsk62

Rotella is designed for desiel engines and will work fine in an XJ. You are right, the thinner 5w-30 and 10w-30 will make your engine a little noisy, but it ok. All you are hearing is lifter and valve train noise. Perfectly normal. Unless you live in a cold wintery climate where it gets below Zero deg 10w-40 is fine. Below that, run a thinner viscosity oil. Most of your Rotella's or Delo oils are 15w-40, which also work great all year round. In the long run, the 4.0L will run just about any oil as long as you stay up on the oil changes and don'y allow the oil to start slugging up.

1991Jeep_Man

Never an issue. I watch oil change intervals like a hawk. Full syns get at most 5k miles. Synthetic blend or dino get 3k.

Just another quick question... would running the thinner 5wXX rather than 10wXX cause any oil consumption? I know both a 5w40 and 10w40 are the same viscosity when hot, but I didn't know if the 5w might allow increased oil consumption? Or vice versa?

1991Jeep_Man

Alright, I'm back with another one. Hopefully to put my heart at rest a bit.

Just to clarrify, because I've got a friend trying to tell me otherwise, isn't it perfectly NORMAL for any vehicle to blow steam from the tailpipe when it's 10 degrees outside? Common sense says " Hmm, cold air, hot exhaust... steam?" I've always been told as long as it doesn't go above your rear window, it's steam. If it goes above the window and doesn't quickly dissapate, then it's something else.

Also, I noticed after starting my XJ to move it and the exhaust was warm, if I put my hand in front of the tailpipe, I had a slight amount of brown residue on my hand along with some condensated water. The brown residue was in random small splotches or splatter. Not mixed. Is this oil?

PatriotGT

by-product of combustion. Steam is normal.

tjwalker

I don't see any actual oil consumption data.....Exactly how much oil is your engine using over 1000, 2000, 3000 miles? IE; how much do you have to add to bring you back to where you were at when you changed the oil? Trying to extrapolate any other way isn't of much value. You need hard data in order to determine if your engine is actually burning oil and if it is at a level of concern or not. Burning a bit of oil with a high mileage engine is not unusual or anything to be concerned about.

And yes, water is a byproduct of combustion. Absolutely normal. The slight brown residue that you're getting off the tailpipe is most likely carbon, not oil.

I don't see anything that I would be worried about here. Keep a log of your oil consumption over an entire oil change and check back with us.

DFlintstone

Great Avatar Patriot! Love that. I've got ADD and some dyslexia, (or is it the other way around?). it's sort of the way I see things sometimes. Sort of.

Yea, perfect combustion yields carbon dioxide and water. Less complete you can add carbon monoxide and hydrocarbon. (unburnt fuel). Nitrogen Oxide needs nutty high temp and pressure to form. (hence the EGR to muck things up!)
Gotta wonder if the brown isn't rust?

1991Jeep_Man

I'm an idiot. I did forget to post up my records.

The reason I hated the Pennz platinum was because I seemed to burn over the oil change interval a large amount of oil. I drove a 3 hr trip, all highway driving, about 190 miles, and burned about 3/5 qt oil. This was with Pennz Platinum 10w30 and no CCV maintence, leaking valve cover, etc. I would bet all that oil wasn't neccesarily burned.

Switched to Mobil 1 full synthetic HM, 10w30. Before maintenance, noticed slightly less oil loss; same trip only lost maybe a tad under/over 2/5 qt oil. Over a period of time, I replaced the valve cover gasket, at which time I also replaced the the CCV grommets and cleaned the internal baffles. Also replaced the oil filter adapter o-rings. With each repair, oil consumption became less and less until I was at about 1qt every 1100 miles. This was also in combination with a variety of additives (Lucas, Restore, etc.) that I tried at varying intervals. I feel these additives were wasted money, especially the lucas. I think the Lucas cause my PureOne filter to fail.

Recently, I switched to Mobile 1 full syn HM 10w40. Love the result, and I noticed much less oil consumption. Granted not much of my driving was actually on interstate, however how much of a difference in oil burning can there be from going between idle and 3000 rpm in the city constantly and crusing at 60 mph on rt 11? Even under these conditions, my oil level stayed in the safe zone the whole interval, which was a short 1000 or so miles. The reason it was so short is because with colder weather I really wanted to run the Rotella T6 5w40 for easier start up and less wear.

When I switched to the Rotella T6, I think I hit my perfect zone. I think that oil change was about 2 months or so ago, with random bits of driving to and from town, through town, running errands, etc. Everytime I checked the oil, it was always right on the same spot. No issue. And I am wondering if the oil level I was seeing before was the same as it is now, but the oil reflected or something, because everytime I have changed my oil for 2+ years now on this Jeep, I have NEVER overfilled. Right now, I am sitting right at the top of the safe zone. Perfect level.

Edit: Also, I take a lot of short trips in the Jeep when I run errands. I run into town, and then run from place to place. Never do I have puffs of smoke or anything on start-up.

1991Jeep_Man

Wouldn't surprise me. As much as I want to replace it, the downpipe is the stock 21 year old unit.

salad

For the sake of completeness (hey gotta get my post count up somehow :P) the catalytic converter is there to cleanup after the hydrocarbon burn. The main function is to convert NOx, leftover fuel vapors, and CO into the less dangerous CO2 and water by way of heat. Older cats inevitably have crap coating them, so they take longer to warm up. So, say, in the winter, you might start the engine with almost no visible exhaust, and as it warms up you'll see plumes of steam. In the summer the exhaust/air temp difference is less so the steam gets a chance to condense, and you get water dripping from the tailpipe.

tjwalker

1991JeepMan, I'd just drive your Jeep and keep logging anytime you add oil. You may be overly concerned here. I had an older XJ that burned some oil and I kept a small notebook in the glove compartment and noted in there whenever I added. That way, I could see how I was doing, the progression of oil consumption, and if I needed to be more concerned about it.

Oil consumption on older high mileage engines is not a death sentence. I've seen 4.0 engines run for tens of thousands of miles with moderate oil consumption.

As long as you are sure you have a clean CCV system, drive it. If you want a data point (and I love data points) run a compression test on all cylinders. It isn't difficult and is a good "snapshot in time" of the internal condition of the engine. The spec. compression for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders. If you don't have a compression gauge, they can be rented from many big box parts stores. Run the test dry, then add a teaspoon of oil to each cylinder and re-run it (wet compression test). SEARCH the web for interpreting these results but in general, if the compression is low in any cylinder and comes UP with the addition of oil, you have worn piston rings.

And skip the oil additives. Mobil 1 full synthetic is a fine oil; you certainly need nothing more. You aren't getting any value out of the additives here. And adding them and not adding them introduces a "variable" that gets in the way of logging your TRUE oil consumption.