BSOD; Blue Smoke of Death

[BMWDriver]

I've noticed some heavy oil consumption lately.

Being in town, I have to move my car twice a week because I have no parking of my own, like many in my neighborhood. So I don't go far, and naturally, I sometimes go out of my way for a little ride, because of what too many short trips can do to the engine. (The subway close by, I don't commute to work with Baby.)

Yesterday, I take one of those trips, and upon start, I see a nice cloud of smoke coming out when I press hard on the gas, as I stood one foot in the car, door open because I wanted to see. And it smelled. It's almost like oil accumulated and then got spewed out. Otherwise, afterwards all seemed fine.

Well, it is an old engine.

But after taking it for a trip 'round the block, I do some minor maintenance (clean, touch up paint, winter prep) for about a half hour. I look at the engine, and don't see much of a leak, but still think maybe a change of head gasket is in order. After I restart the engine, I do the same with the throttle, but this time, no smoke, if hardly any, and no smell.

The engine sounds really well and steady. I would not think the pistons are at fault, but I'm far from expert on this. So I doubt a rebuild would be in order.

Come to think of it, I should post pics, but it's getting too dark early for that this week.

Your thoughts ?

[whiskychaser]

I've noticed some heavy oil consumption lately.

Being in town, I have to move my car twice a week because I have no parking of my own, like many in my neighborhood. So I don't go far, and naturally, I sometimes go out of my way for a little ride, because of what too many short trips can do to the engine. (The subway close by, I don't commute to work with Baby.)

Yesterday, I take one of those trips, and upon start, I see a nice cloud of smoke coming out when I press hard on the gas, as I stood one foot in the car, door open because I wanted to see. And it smelled. It's almost like oil accumulated and then got spewed out. Otherwise, afterwards all seemed fine.

Well, it is an old engine.

But after taking it for a trip 'round the block, I do some minor maintenance (clean, touch up paint, winter prep) for about a half hour. I look at the engine, and don't see much of a leak, but still think maybe a change of head gasket is in order. After I restart the engine, I do the same with the throttle, but this time, no smoke, if hardly any, and no smell.

The engine sounds really well and steady. I would not think the pistons are at fault, but I'm far from expert on this. So I doubt a rebuild would be in order.

Come to think of it, I should post pics, but it's getting too dark early for that this week.

Your thoughts ?
Sounds like oil leaking down past the valve guide oil seals. Try going down a hill gently on the over-run at about 20mph for about 100 yards. Then put your foot down. If they are that fkd you will see a blue cloud in your mirror. Be scientific too- try compression and leakdown tests.

[Dave M]

Sounds like oil leaking down past the valve guide oil seals. Try going down a hill gently on the over-run at about 20mph for about 100 yards. Then put your foot down. If they are that fkd you will see a blue cloud in your mirror. Be scientific too- try compression and leakdown tests.

If we're trying to increase vacuum to determine whether its being sucked past the valves, it may also suck past bad ring (s). As you said, comp test (dry and wet) as well leak down will provide better results. I've had the same symptoms and it ended up being a result a bad ring.

Dave M

[BMWDriver]

Thank you both, duly noted.

[Jeff N.]

Generally, smoke on accel is rings. Smoke on deccel is seals or guides.

[Dave M]

Generally, smoke on accel is rings. Smoke on deccel is seals or guides.

Can you really get smoke from valves under decel vacuum conditions? I'm aware that oil can be sucked past valves/rings under decel vacuum and then visibly burned under subsequent acceleration.

Why is accel rings and decel valves.

Curious,

Dave M

[Jeff N.]

Hi Dave,

If the guides and seal are really bad, then yes, you can get smoke on decel. I think you're correct in that the more typical scenario is smoke immediately after decel.

You answered your own question on why you get smoke on decel with bad valves - vacuum. Accel is just the opposite - poor ring sealing allows oil in the combustion chamber.

[whiskychaser]

Hi Dave,

If the guides and seal are really bad, then yes, you can get smoke on decel. I think you're correct in that the more typical scenario is smoke immediately after decel.

You answered your own question on why you get smoke on decel with bad valves - vacuum. Accel is just the opposite - poor ring sealing allows oil in the combustion chamber.
How about a decider before the comp/leakdown tests are known? Blue smoke when its fired up first thing in the morning and which clears fairly quickly is valve guides/seals-caused by oil running down into the combustion chamber overnight?

[BMWDriver]

Well, I have come down a ramp slowing down and stopping at lights right there. Then as I had to give power to get out of a messy situation shortly after the green light (a strange intersection that was anyway), I saw a puff of smoke out the back in my mirrors.

We're close I think to all of your diagnostics.

Will keep you posted.

[Jeff N.]

That's pretty much a cylinder head problem - seals or guides. But it you're not burning a lot of oil, who cares?

Also, with as many miles as you have, if you seal up the head you'll likely have some more blowby problems at the bottom end. I'd spend the money on a compression and leakdown test before you decide to invest anything.

[Barney Paull-Edwards]

Before you collapse you credit card,clean the whole crank/rocker box vent system,if you run on cheap fuel like the rest of us and the pipes are old it wont do any harm and might be the answer.

[BMWDriver]

Well, it's pretty inconsistent. No smoke on start this morning, nor a few days ago. It's somewhat good news. I probably should leave it as is for now. It seems to happen on somewhere around full throttle though... but only on occasion.

[taseal]

kinda bringing an old thread up but i'm having similar problems :(

did you figure out what it was, or just left it? how much oil ya burning?

[BMWDriver]

Talked to the mechanic too, and being that it's really occasional, he said it's only normal considering the high mileage. There are no other serious problems, so I'm quite content with the way things are right now. So I just leave it as is for now, and perhaps an engine swap some day.

I haven't calculated how much lately, but I remember about every 2000-3000 kms I had to add a liter before I had switched over to synthetic. The PO had regular.