Okay, I searched around and found a few things that kind of corroborated what I thought, but I kind of wanted an opinion from those who know infinitely more about the 4.0 than I do.

It's a '93 XJ with the 4.0. About 194,000 miles. It runs fantastic, smoothly, no misses or hesitation or anything of the sort. A little rattly up top but, from what I gather, that's about normal for a 4.0 with that kind of mileage on it.

I was checking out a possible future fishing spot the other day, and got out of the Jeep to look around. While I was out, and the thing was in Park and idling, I noticed a small puff of blue smoke escaping from the exhaust. Being constantly paranoid about all engine noises and issues, I ran over to it for a closer look, but by then it had dissipated and was normal again. Exhaust smelled, er, like normal exhaust. I noticed the same thing a few days later... car was idling, the electric fan kicked on, and a tiny puff of blue wafted from the pipe. By the time I got there to look, it was gone and all was normal.

My pessimism yells "Piston rings!" but I'd think, were that the case, I'd be belching blue smoke all the time, or at least under load... which it isn't. The engine isn't eating a tremendous amount of oil, either; at least not that I can't account for with the normal elderly oil pan gasket leaks. I changed the oil about 900 miles ago and have only had to add maybe half a quart since.

So I'm kind of thinking valve stem seals. I was also mentally entertaining the notion that it could be because I changed the oil to a synthetic blend (and some Marvel Mystery Oil, because I'm a sucker)... I figured I'd give it a shot and if it sucked, just go back to the conventional. But in my brain, maybe the synthetic bits are getting past the seals that'd stop the fully conventional junk from getting past.

Otherwise, though, she still runs like a champ. I'd just like to keep it like that.

Any thoughts?

 

Maybe the new synthetic oil loosened up some guck that was providing a kind of seal?

 

A little puff in an old motor is just upper cylinder lube, lol, no biggie.

 

Could be worn valve guide seals. Just keep an eye on the oil level and enjoy you rig for thousands more miles.

 

One sign of guides/seals, if you park it hot, then go back, say in 1/2 an hr and watch when you start it. If oil ran down past the seal into the cylinder it will "puff" (or more!)

I'm on a pretty good hill, more then 5 minutes decelerating in low to get down. I had a Toyota that would suck so much oil past the rings going down sometimes I'd stop a few 100 yds from the hwy and blow out a bunch of the smoke. I still got stopped right there once, I just got a warning when I promised the CHP he wouldn't see it on the road until I dealt with it. He was right, it looked bad even though I was still going 1000 miles on a quart. That was years ago of course. Everything is a ticket here now. Once my trailer chain came undone. I had to pay a paperwork fee and got wrote up, even though I hooked it up right there!

Anyway maybe it's fine if you just have a little puff now and then.

 

My money's on valve seals if it puffs only at idle and you can't see a trail of blue behind you after decelerating.

The 175,000 mile engine I got from the JY did this, too. Didn't really use oil but puffed at stops. Put new valve seals in without removing the head. It doesn't use a drop of oil between changes and no more puff.

 

I know several people who make valve stem seals, they are designed to leak. Some just leak more than others.

 

Especially if they're old and brittle after many miles............

 

It seems like (something) improved quite a bit. Was defiantly common, even normal for them to harden and cause trouble. I gave up on a aluinum V6 in a 63 Buick Special doing them with compressed air, before I knew the "cord trick".

 

Phew, thanks everyone... that makes me feel a bit better. I always fear the worst with anything vehicle-related.

I let it sit for a while and started it up again after about half an hour... no sign of blue smoke. And nothing while driving or accelerating. A little bit of normal condensation after a cold start this morning, but then it was also raining for a lot of the morning so I'd kind of expect that.

I was planning to change the oil again in about 100 miles or so, I figure I'm going to go back to conventional. I wish I could find something decent... all the shops seem to carry is stuff like Pennzoil, which I've always been under the impression is junk. I ended up using a Quaker State synthetic blend last time because it had zinc and... additives. I've heard good things about Valvoline Racing -- which I can't find -- and Rotella-T, which is evidently a full synthetic and I'm paranoid about going to that after so many years of regular conventional.

So I'll try that, and I'll keep an eye on the levels. Hopefully it continues just as it is, and if it gets any worse I'll look at replacing the valve stem seals.

 

Basically, every engine burns a tiny bit of oil, even new ones. If they didn't, they'd seize up! A little blue at idle is nothing to worry about with that kind of mileage, mine does it too on really hot days, but i've got 250k on mine!

 

Get Rotella at Wal-Mart. I don't believe the T is synthetic..........

 

I just run 10-30 Valvoline. I've got over 300k on mine.

 

Not to try and start a war over oil, here, but my XJ has 313+K miles on the original engine and since '97 I've used nothing but Pennzoil 10W30 and more recently 5W30 in it. Still runs great, too. It's also had mostly Fram filters in it as well, not to try and start a different war...

I think its more about how aggressive your preventive maintenance is and how often you raise up the hood and check things out.

 

Heh, not trying to start an oil/filter war. I have a mild superstition regarding Pennzoil, which has nothing to do with the quality of the brand but simply that I've only used Pennzoil twice, and both times, the cars spun a bearing like two weeks after I changed the oil. I'm pretty sure that it was entirely coincidental, but then... I also refuse to put "New Car Scent" air fresheners in the car because the two times I did that, the car blew up soon afterwards, too.

Either way, my main concern wasn't necessarily over brand, but mostly over whether they add the zinc and... additives... to it. Only one I could find that did was the synthetic blend, so I used it despite being mildly wary. 10W40, because, er, that's what I've always used.

Also used a Mobile-1 filter, but swapped that out a couple of days later for a Bosch for no reason other than that I was changing the oil in my girlfriend's car and the store had given me the wrong filter... and apparently a '98 Honda Civic and a '93 Cherokee use the same filter. I had the Bosch already (in case I didn't like the synthetic and wanted to change it, I'd gotten two filters and enough oil of both kinds), but it was too big to fit in her little engine... but the Mobil wasn't, so I just gave her the two-day-old filter off my Jeep.

Blabity bla. That has no relevance to anything, and I'm apparently rambling. It's been a long day.

But yeah... the vast consensus that I see is that the 4.0 will be happy as long as there is any oil at all. Which is kind of reassuring. I've got Valvoline conventional for my next change, which'll probably be in a few hundred miles (having just got the thing, I like to make a few oil changes at 1000-mile intervals, for no reason other than, well... probably superstition again). Heh.