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Burning oil


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Recently changed to synthetic oil, Syntec 5W50 from Castrol 20W50. 77 280z has 37k original miles. Engine has good compression and works well. But, has started to show a little oil smoke when rpm > 4500, none below. Oil consumption is 1 liter (qt) /2500 miles.

Switch to synthetic probably losened some dirt/varnish that has caused the oil rings to stick allowing some high rpm blowby. Pcv valve is good.

Considering an engine flush to free up/clean oil rings.

Any experience or recommendations re my situation/strategy??


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Here's my guess... Since it is low miles, but has age against it I would guess you are sucking oil past the valve guide seals since synthetic is a lot slipperier and only 5 weight. That and the fact that it only happens above 4.5K, there's a lot more oil on top then than at lower r's. I'd install new valve guide seals and try again, cheap fix and it wouldn't hurt.

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Your diagnostics are good.

I forgot to mention that the head was professionally rebuilt last year with new valve guides and seals when the old head gasket failed and needed to be replaced.


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Close but no cigar!!

Well Don, you're making it tougher :) Since the head is rebuilt that can pretty much be eliminated. Seems strange that it's only at hi r's, if it was rings I would expect it all of the time. You can try an engine wash, I have no experiance with them so don't know if they really work. If you try it and it doesn't help I would probably switch back to regular oil. Eventhough you are not burning that much I wouldn't want to be adding that carbon to the combustion chamber along with the added plug fouling.

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