My old wagon, NA/standard, has 110k on a rebuilt B21f with Jetronic-K injection (everything standard equipment). It uses a quart of oil around every 600 miles, but no visible smoke...

EXCEPT--sometimes when I stop just for a moment, say at a stop sign, then start off, the engine knocks loudly (the only time it knocks, otherwise it's happy on regular) and it lays down a major smoke cloud. Makes me look like a one-man ozone hole.

Then I can drive away and it runs like there's no problem. This happens only after the car is thoroughly warmed up. It also doesn't happen most of the time--just at random moments when I'm not expecting it.

What's going on here?

Thanks for any help you can provide.

Doug Harvey

Here's an idea, born of an experience I had with a 1960 Ford 390 V8 many decades ago.

As the engine revs are dropping down to idle, manifold vacuum is at its highest. Somehow there is oil being sucked into the intake system.

While you are driving at a "normal" speed, the vacuum is not as high and/or the oil burns off at a lower rate, so any exhaust change would be hard to detect. But, at idle, the oil builds up, so when you accelerate there is a good bit of oil, and it makes that gawdawful cloud of smoke out the rear.

This theory would also mean that you don't see that cloud when first starting a cold engine in the morning. Is there a cloud then?

Why the knock? Well, I would guess that if your usual gasoline had enough oil vapors blended with it, the octane rating would drop substantially.

Check the entire PCV system for excess oil. You might also run a compression test, including the adding of oil to find weak rings, to find out if you have excessive blow-by. Have a look at the plugs, too. The problem should leave them black and sooty, I would think. Another source of oil would be leaky valve guides.

Let us know what you find out.

Good Luck,

Bob

:>)

I have a 68 chevy pickup 250 straight 6 (I also own 6 Volvos). Every time that I would go down the mountain (Hillbilly) and gear the truck down for a mile or two, it would puff blue smoke at the bottom upon acceleration. Compression checked out OK, so I figured it must be in the head. Turns out the valve guides and rubber seals were worn. I replaced the guides and seals and eliminated the problem. If your engine was rebuilt, it is possible that the existing guides were knurled (deformed inside and re-bored) instead of being replaced. In my experience, knurled valve guides do not last as long as new guides. Unless you are equipped to change the guides, you will have a machine shop do the work. (You can take it off yourself to save $$).