69S with strange smoking engine problem - help.

[rngpc]

I recently purchased a '69S and am trying to figure out why the engine is smoking. When I initially made contact with the former owner, he told me he had a dealer rebuild the engine back in the 80s and it ran fine with no major smoking problems until 2 yrs ago when he took the car to a 10 min oil change place. He had the oil changed and the car came back smoking like a freight train. He then parked the car in his garage and it hasn't been driven until a couple of months ago.
The first time I looked at it, it was blowing a little black smoke, no gray or blue smoke - I figured it was running too rich. I then inspected the car a second time prior to having the engine looked at it was smoking like a chimney - clearly burning oil. We shut the engine down and I sent it off to be inspected.
Well, I had a leak down test performed with all cylinders between 4-6% . I went ahead and made a deal on the car. Several small oil leaks have been repaired and it was thought that maybe it was overfilled and oil had made its way to the muffler and it was buring it off. This doesn't appear to be the problem as the car has been run several times over the past couple of weeks as general maintenance items have been taken care of.
Now, sometimes it blows smoke like crazy and other times nothing. Any ideas what could be causing oil to be burned periodically and not continually? I know that valve guides could still be worn even though it has a decent leakdown, but is there anything else that could result in these strange symptoms? Any replies are much appreciated.

[BBausser]

My 67S has a similar problem. I think it's leaks on the heat exchanger that eventually burn off. It goes to the resto shop this week and hopefully in a year or so won't be a problem no mo

[glaverbel911]

Worn or Broken oil ring or intake valve seal gone bad.. You'll have to isolate the problem by inspecting each plug to see whiich is the oily one.
Also,, make sure the air cleaner breather line to the oil tank is not switched with the crankcase breather line to oil tank. This could cause the problem as well creating pressure in the engine case and forcing oil past the rings.

Robert..

[rngpc]

I appreciate the replies, I will pull the plugs and take a look.

[spydr32000]

Have you checked the oil level?
I know that sounds like an odd question, but, if the oil has been over-filled, then it can cause foaming of the oil, pushing it into the air cleaner and causing smoking. This will normally occur if the engine has been driven hard. I have seen it happen if the oil is severely over filled. These people should NOT be allowed in the same hemisphere as a 911!

[69911T]

Ditto on Mike's thoughts. The oil tank can be over filled and this condition often times will not make itself apparent until the oil gets warm and expands and then is pushed out where ever it can go, usually into the air filter box.

You didn't mention oil temperature. Is the oil/engine getting hot???
Check the engine thermostat...a real hassle...they do fail and cause heating/smoking.