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.

?(C) 1999 by Tom and Ray Magliozzi and Doug Berman
Distributed by King Features Syndicate, Inc.