Change oil
There's several answers to that question. The "best" oil is what the manufacturer recommends in the owner's manual. You can also make that decision based on several things including the type of driving you do, the temperature you most operate in, and personal preference. I have found that over the years simply using the recommended weight provides the best resutls.
Some folks use synthetic oil because they feel they get better performance. Personally I don't use synthetic oil in a car that didn't come from the factory with it. I've run several cars well over 200,000 miles by following the owner's manual without a hint of trouble.
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