Ok, at ~170K, it's unavoidable, it needs serious work. Runs well, but oil consumption is out of control. And occasional major smokescreen on startup. Far from always, usually, but not always first start of the day, but massive, profoundly embarrassing cloud, not just a puff or bit of burnoff. It's bad. Real bad. And oil consumption is more than a quart a thou. I could deal with adding oil, but not the smokescreen.

Questions.

I've done lots of engines in my time, more than I can remember, admittedly none as complex, but that's just detail work. But right now I'm not set up to pull an engine. So, first off, can I pull the sump, AKA upper pan (?) without pulling the engine? If so I'm guessing I should be able to do rings and bearings in place. I've looked at the manual and it's not really clear.

Speculating, but I'm guessing it's a victim of cat failure/EGR etc. Shortly after purchase 40K ago I pulled the after cat O2 sensors and one was black and sooty and the other was a nice gray. Might be the power valve screw(s) but I'm guessing cat failure. So, is that honeable? Does it need a bore? Pistons or are the rings just trashed? Can I hone aluminum, normally not, but it's a special Al, so maybe? If not with a cylinder hone, then how? How much wear is typically present? Bore and new pistons? I really don't want to go there.

Any other suggestions or words of wisdom?

If it was cat failure, it probably didn't inhale it. You'd have dead misses on the affected cylinders. If it's still hitting on all six then it's probably just worn out, not a cat-tastrophe. However, rebuilding VQ's is a very unforgiving PITA and I don't know anyone who does it routinely, especially not in situ. Dunno which type you have, I have seen a few DE's successfully overhauled but no VVEL ebgines (the VVEL heads aren't rebuildable and replacing the engine wholesale is a better idea).

I believe it is the VQ35DE, in an '03 QX4. It is definitely still hitting on all 6, subtle changes can be difficult to follow, but it seems to run the same as 40K ago when I got it and it used some, but not that much oil. But currently it's "that much" oil unfortunately. Curiously no CEL which portends well if I want to sell it, full disclosure obviously, but still significant.

I have considered buying an engine, but looking at Car-Part they're not that common and I'm fearful of getting just what I have, an engine that runs well, but is a pig for oil. 170 doesn't seem high for worn out these days, but I'm no Nissan expert. I've also considered buying an engine, rebuilding it and paying the guy 2 doors away who does more sidework than some shops do in total, to do the swap.

Have you run wet/dry compression on it? Clouds at startup are more characteristic of bad valve seals then scrubbed rings. That's still a major exercise on a VQ, but a lot less serious than a bad bottom end. If the compression checks out, I'd also advise taking a fine tooth comb to your PCV system before condemning the seals. A weak PCV Valve or collapsed hose can easily cause a whole lot of oil consumption for no apparent reason.

No, I have not run a compression test on it. I've even bought a 'scope tool, specifically for this to look in the spark plug holes, into the cylinders, which I have not as of yet used.

Every engine is different I acknowledge, and I've had a couple that smoked at start up, but never, ever, anything like this can. But not always. But it does drink a lot of oil regardless. It doesn't "seem" like bad VG seals, and as I said, I've had a couple of them. But that's not a definitive statement. I don't know Nissans that well yet, are VG seals buna-n, which get profoundly crispy with miles, or Viton which is nearly impervious to engine heat. I've thought of the PCV, even bought a replacement, still sitting in a box, before I found out how difficult replacement is so I haven't gotten in that far yet.

I've rebuilt this engine. There is a thread on it here. Yes, it's the rings, it's a known severe wear item. Mine doesn't burn oil after the rebuild, runs outstanding. But I had to put around $4k into it, pre-inflation.

My advice is don't bother trying to do it if you can't pull the engine, because 1. there is no way you'll be able to keep things clean, 2. you won't be able to pull the rear coolant bypass, and 3. you won't be able to pull the heads.

Also, don't pull the trigger if you don't have the funds because once you tear into it you'll find a thousand things in need of replacement.

I see hoists on Craigslist and FB Marketplace every day, would that be an option for you? Do you have a clean garage with a level floor?

Yes, I recall your thread clearly and even commented in it a couple of times. But thanks for confirming what I feared. I probably should do some more troubleshooting, but it screams rings to me. Mine is arguably in much better shape than yours was, no odd sounds and it absolutely runs like a top, it just drinks oil like crazy.

Ironically I sold a hoist around the start of the pandemic thinking I wouldn't be using it again, and it was in the way and taking up space. I guess I could pull it in my garage, it's only got an 8' ceiling though. I would be cramped for space as my driveway is steep so I'd never get it back in if I backed it out. Decisions decisions. Hmm. I really ought to cut my losses as I believe it will still pass smog as no CEL on yet.

Perform a cylinder compression check dry. Then do one after squirting a few drops of oil into the cylinder. If compression is higher in the cylinder after it is wetted, it's the rings.

I got it a little bit apart today, as always, great pans and unexpected occurances. Anyway, I pulled 2 plugs and used my new 'scope tool to look inside. Not positive the pic uploads will correspond to the description, but the black one is #6, the gray is #2. Pics are at once astoundingly good and lousy. For what I paid for the 'scope, it's a steal. Is it the ultimate tool, no, it is not.

#6


#2


Now there might be some damage on #2, it's not smooth as silk visually, but looks ok, but the black oily look on #6 does not make me happy or optimistic.

#2 spark plug, looked perfect, except to my eyes, high mileage. Supposedly plugs were changed with the previous owner about 40K ago. They do not look way high to me. But #2 was a nice gray, just like it's supposed to be.

#6 spark plug, didn't actually look bad, but not as good as #2. A little on the black side, but not oily. Gray in the middle. Pics I took of the plugs didn't come out.

I see a big problem in #6. I haven't gotten in as far as the PCV, which I still want to try, but I fea damage on at least #6 cylinder.

Edit, and I don't see that function in spite of it being available on other php forums.

Anyway, no big deal but the plugs look to be very high mileage, probably original, not replacements as I was told upon purchase. Exaggerating a bit, but it looks like I can stick my little finger into the gap. Still, even on the suspect #6, it looked worn, but not bad. Blackish on the outer circle, but dry, and nice clean gray on the inner portion with some tan deposits.

Looks more like #2 has the issue. That's way too clean. Carbon on a crown is normal. The only thing which usually shines one like that is a blown head gasket, the temperature difference between the metal and the coolant blows all the carbon away..