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My 88 740 Turbo Wagen (5sp, 150,000 miles) has developed a smoking problem. This happened at 90,000 miles and I took off the turbo for a re-build. At that time the bearing was shot. This time the turbo seems to work ok (there is boost.) I turned the turbine with my finger. It had firm resistance but turns smoothly. No shaft play. Cleaned the oil seperator, hoses, drain tube from turbo. Still smokes. Haven't done a compresion test (don't want to find out its a ring).
It does stop smoking for about a minute after running 5 minutes of highway drive with plenty of turbo boost (morning race to work). Maybe all that spinning helps to temporarly seal in oil?
Tell me its the Turbo. I'd hate to spend $300 to find out it a ring. What kind of compresion differential clearly shows a bad ring?
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