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I've heard that from a lot of different people but can't seem to get a consistent reason why. What's the reason you don't run synthetic oils during break-in? Ring seating?


becuase it's too dang good at preventing wear.
there are more than a few that say the rings and bearings won't run in right unitl they got some solid wear between everything. that bieng said, every new corvette is delivered from the factory with Mobil 1 synthetic in the crank case. personally, I ran the first 20 minutes on my new motor with non-synthetic.