Dear Tom and Ray:

My co-worker and I are having a disagreement about oil changes. Our question: When changing oil, is it advisable to use the same brand of oil all the time? I have always used the same brand, and think this is the way to go. She feels that as long as the oil is changed every 3,000 miles, it doesn't matter which brand is used, as long as you use winter- or summer-weight oil appropriately. Thanks. -- Jacki

TOM: I hope you don't have a lot riding on this, Jacki, because your co-worker is about to collect. She's certainly more correct about oil changes than you are.

RAY: Motor oils are incredibly similar. And even the same brands sometimes alter their formulation from time to time to make their oils better ... or cheaper.

TOM: There are only a few things you need to look for to make sure the bottle of oil you're buying is suitable for your car. First, you want to look for the API seal. That's the American Petroleum Institute, an organization that certifies that motor oils meet the cooperative standards set by engineers, manufacturers and graduate students in chemistry.

RAY: Next, you want to use the grade of oil recommended in your owner's manual. There are really no "summer" or "winter" weight oils anymore except in the most extreme climates. Most cars use a multiviscosity oil like 5W-30 all year 'round (which performs like a 5-weight oil in cold weather, and a 30-weight oil in hot weather), but check your manual to be sure.

TOM: Then check the performance level. API changes the ratings as standards improve, and you want to be sure you're getting the latest and greatest additives and technology. Currently, "SL" is the highest-rated oil for gasoline engines.

RAY: And finally, you want to be sure that the bottle doesn't say something like "may contain small pieces of dinosaur bones." That would suggest that it hasn't been in the ground long enough.

TOM: You can change your oil every 3,000 miles if you're really particular, but we recommend changing it every 5,000 miles at most. Today's oil is good enough to easily go more than 5,000 miles. So if you change it more often, you're just wasting your money and creating a disposal problem.

RAY: Right. Other than using it on his hair and in his salad, my brother can't figure out what to do with all of our used oil.