Dear Tom and Ray:

I recently bought a 1995 Infiniti J30t. It specifies to use only "premium" unleaded fuel. I'd like to experiment and see if I could safely save some money by using some portion of "less than premium" fuel along with the high-priced stuff. Can I do this without harming the car? And while I've got your attention, do you have a preference in gasoline brands? -- Conrad

Ray: Well, Conrad, we don't have a preference among gasoline brands for two reasons: 1. They're all basically the same, and 2. None of them has offered us a huge advertising contract to date.

Tom: And the answer to your question is no. I don't think you should use lower octane gas in this car over a long period of time. If you wanted a car that burned regular gasoline, you should have BOUGHT a car that burned regular gasoline.

Ray: Most modern cars have knock sensors, which detect pinging, which is often caused by the wrong grade of gas. When the engine pings, the computer retards the spark timing to compensate for the lower octane. That's designed to prevent engine damage if you get a bad tank of gas or travel someplace where the correct octane is unavailable.

Tom: But it's not a good idea to run your car with retarded timing over the long run. Among other things, you'll force the engine to run hotter than it's supposed to run, which will shorten its life. And you'll force it to run rich, which can eventually ruin your catalytic converter.

Ray: So I'd say you're stuck with premium unleaded, Conrad, at whatever octane the owners manual recommends. It's a good reminder to the rest of our readers. Before you buy a car, find out what kind of fuel it requires. If you don't, you may be unhappy to discover that you're going to be out an extra 25 cents a gallon at every fill-up for the foreseeable future. © 1999 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

To buy or not to buy -- options, that is. Are options worth what you pay for them, or are you better off just going with the basics? Order Tom and Ray's pamphlet "Should I Buy, Lease, or Steal My Next Car?" to find out. To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1999 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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