Dear Tom and Ray:

I have a 2009 Nissan Cube. I take the car to the dealer for oil changes. I always use synthetic, but at the last oil change, they put in regular oil by mistake. I drove the car for 3,000 miles and then asked them to put in synthetic oil. Now my husband says that I have "ruined" the engine by switching the oils back and forth. Is this true? He says that I immediately should have asked them to drain out the regular oil and replace it with synthetic before I drove the car away. What do you think?

-- Mary

TOM: I think he's got his head up his oil drain, Mary.

RAY: When synthetic oils first came out, we heard rumors that you shouldn't switch from regular oil to synthetic, or vice versa. But we never saw any proof that this was more than a rumor.

TOM: And now several of the major oil companies sell synthetic blends, which are what? Mixtures of regular oil and synthetic! So they mix them right at the factory.

RAY: So obviously, no harm is done by mixing them in your crankcase, or switching from one to another.

TOM: So drive happily, Mary. It sounds like the only thing you ruined here is your husband's credibility.