My car has 90k miles on it and I recently changed to synthetic. Actually at my last oil change, I put in 3 quarts of Mobil 1 synthetic 10w-30 (that's all they had), and then 5 quarts (a big jug) of Mobil 1 10w-40. I have yet to have any leaks, and car runs as good as ever. My next oil change is going to have 5 or 6 quarts of synthetic, and 2 or 3 quarts of dino, respectively.
I'm doing a transition just to make sure it goes ok. I am going to push oil changes to 4k or 5k with the partly (and then fully) synthetic oil.
But everything's fine so far!
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