Dear Tom and Ray:

I just bought a new Mazda, and the owner's manual states that I should use 0W-20 oil. I wonder if that is too lightweight for summer travel at interstate speeds, and would it not cause the engine to wear more than using 5W-30?

The vehicle is a CX-7 with a 2.5-liter I-4 non-turbo engine. I like getting 100,000-plus miles on my vehicles: I currently have an '03 Protege with 120,000 miles and a '97 Toyota with 140,000, and I would want this CX-7 to get that kind of use. Please advise on your feelings about this 0W-20 oil.

-- Jim

RAY: It's good stuff. My brother uses it in salads.

TOM: For years now, car manufacturers have been pressuring oil companies to make oil better and less viscous. And they've done it.

RAY: Just because oils are less viscous (thick), that doesn't mean they don't lubricate, dissipate heat or protect well against wear and tear. It just means they do all that stuff while creating less friction, which means you get better mileage and longer engine life.

TOM: You're probably not old enough to remember when cars routinely took 40-weight oil in the summer and 20-weight oil in the winter. That stuff was real sludge. You could still see the dinosaur bones in it.

RAY: Then, multiviscosity oils were invented. So, for instance, you could use a 10W-40 oil that would act like a 10-weight (thinner) oil when the temperature was low and a 40-weight (thicker) oil when the temperature was high.

TOM: And, through the years, as lubricant technology has improved, the viscosity of the oils has dropped, to the point where we can now use a zero-viscosity oil in cold weather. That means the engine uses less energy to push its parts through the oil. That energy goes into miles per gallon instead.

RAY: It also means the oil coats the inside of the engine more quickly --in a fraction of a second after startup -- which protects the engine from wear and tear during cold starts, and makes it last longer. It also means the engine starts more easily in cold weather. Pretty good stuff, huh?

TOM: We've seen no problems as cars have gone from 10W-40 down to 5W-20. And while the 0W-20 is fairly new, I don't expect any problems from that, either.

RAY: That said, most vehicles have "severe duty" recommendations in the owner's manual. They'll tell you that if you're planning to climb Pike's Peak with a trailer, if you're using your car as a taxi or if you live where it's regularly above 100 degrees out, you qualify for special maintenance procedures. Those can include more-frequent oil changes and/or use of a different oil.

TOM: So, if that describes you, Jim, check your owner's manual and look up the severe-duty recommendations. But if you're just driving the car like the rest of us, I'd go with what the manufacturer suggests.