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I've a similar problem, compressions are 150,150,152,145,150 and 152. Vacuum is at 20 in hg. PCV vacuum test lowered cranking vacuum by 3. I ran synthetic in it until I found everyone here runs 20-50 dino oil so I changed to it and after 400 miles it still smokes at startup and under heavy loads. The engine was reported as a recent rebuilt by the seller. I'm losing about a qt. every 350 miles. I think it is the valve guide seals. I don't know how you can lose a qt. of oil in thirty miles w/o some kind of engine failure in the near future. Now I've also heard that synthetic oil glazes the cylinder walls but that must be with new rebuilt engines cause you wouldn't get high compression values...would you?
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