QUESTION: I was taught about 10 years ago in diesel mechanic school that if your engine has over 70,000 miles on it and you did not use synthetic oil from the beginning – don't use it. Is this still true today? I love the fact that synthetic oils are a great starter for cold diesels engines and want to use it in my gas engine. I have 99,500 miles on it, can I go ahead and use synthetic oils?

ANSWER: We do not have the information you seek. You'll need to ask the manufacturer of your truck and of the synthetic you wish to use.

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