Why premium gas is a waste of money

Q: Friends have told me to put premium gas in my two old vehicles—a 2001 Toyota Sienna van and a 2005 Toyota Corolla. They say this will make the vehicles run better. Is this true? I’d rather not so I don’t have to pay the extra costs of premium gas over regular gas.

– Liam, Ottawa

A: The short answer is, don’t bother, it’s a waste of money. Feeding your vehicle a diet of premium gasoline may feel like feeding your pet a diet of premium food but the experts say the benefits are negligible for a vehicle designed to run on regular grade gasoline. Furthermore, the price spread between regular and premium has increased in recent years and is now close to 20 cents a litre in many markets. The best bet is to read your owner’s manual and follow the recommended fuel octane; if you’re offered a choice, regular grade fuel is likely more than sufficient unless you are towing or carrying a heavy load in hot weather. If you’re storing a vehicle for a long period, look for a fuel advertised as having no ethanol, which can contribute to corrosion damage in the fuel system if left in the tank for a very long time.

Chris Muir, an instructor with the Motive Power program at Centennial College in Toronto graciously provided us a more technical explanation:

Octane ratings relate directly to a fuel’s resistance to pre-ignition. Premium fuel requires higher temperatures to ignite spontaneously. Requiring a higher temperature allows an engine to run more compression without risking detonation, or knock. In some vehicles with lower compression ratios, running a higher than prescribed octane may actually do more harm than good. The cylinder pressure isn’t high enough to take advantage of the anti-knock properties, and you risk incomplete burning of the injected fuel. This leads to slightly higher than normal emissions.

Gasoline contains detergents to help keep the inside of the engine clean, but there is no magic cocktail of detergents in premium gasoline. Regular grade fuel will remove oil and varnish as well; good detergents are present in all top tier fuels, not just premium.

Georgy Iny, president of the Automobile Protection Association

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