Wednesday, May 2, 2007

Does My Car Really Require Premium Fuel?

One of the questions we seem to come across a lot is whether it's really required to put premium-grade fuel (i.e., high-octane fuel) in vehicles whose Owners Manuals call for it. We've seen a few articles address this topic recently and this seems to be the consensus:

  • It probably won't hurt your car to put in a lower grade of fuel; and,
  • There may be a drop in performance and fuel economy if you use a lower grade of fuel, but you should test this yourself with a couple of tanks of gas.

As to the first point, Jonathan Welsh--in his Me & My Car feature in The Wall Street Journal--explains that most modern vehicles are equipped with engine-management systems that "adjust the engine's tuning automatically to accommodate a range of fuel grades." But he advises: "In most cases the higher-octane premium fuel allows a car's engine to run at tuning settings that generate optimal horsepower while still operating efficiently. Changing to a lower grade of fuel may result in a noticeable loss of performance, but your car also may run just as well. It's worth trying a thankful or two."

As to the second point, Chris Longhurst over at The Car Bibles explains why (You'll have to scroll down to the "Octane and gas mileage" section, just over a third of the way down) performance may drop with lower-grade petrol. (According to Chris: As the vehicle's engine-management system retards ignition timing to prevent engine knock, engine performance can drop.) He also shares a story of his experience using a lower-than-recommended grade of gas in his engine. (His fuel economy was nearly 20% higher with the higher-grade gas.)

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