I was talking to a friend the other day today about the idea of using synthetic oil in my diesel and how starting is supposed to be easier in cold weather. That is one of the pros, and one of the cons is the extra expense. Then he said he was told that once you switch to synthetic oil, it is not good to go back to regular oil. If this is true, it would nix the idea of using synthetic in the winter and regular in the summer.

Is there any truth to this?

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