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Car maintenance tips

Got gas questions? We’ve got answers

Wheels writer Eric Lai talks fillups, prices, ethanol and more

Published September 22, 2013
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Q: Will the ethanol content of gasoline affect my car’s fuel economy?

A: Federal law requires an average of 5 per cent ethanol content in gasoline sold in Canada, but it’s not uncommon for that amount to be exceeded.

Signs posted on gas pumps typically indicate that fuel may contain up to 10 per cent ethanol. Industry observers say the national average is estimated at 6.5 per cent.

Ethanol cuts certain tailpipe emissions, but also reduces your car’s fuel economy slightly, since it has less energy content than gasoline.

According to the American Petroleum Institute (API), a 10-per-cent or less ethanol blend would have only a slight impact on fuel efficiency. On the other hand, an E-85 blend (85 per cent ethanol) may reduce fuel efficiency by 26 per cent.

E-85 fuel is virtually impossible to find in Canada, although several flex-fuel vehicles being sold today are capable of running on it.

Q: Will keeping my tank near full prevent evaporation and fuel loss?

A: “Technical changes to vehicle fuel systems have virtually eliminated fuel evaporation losses,” states the API.

But generally, it’s better if you always keep your tank at least half full. This helps reduce condensation in winter and you’re less likely to run out if stuck for a long time in an unexpected traffic jam.

Letting your tank run dry or near to it can also damage the fuel pump, which is dependent on surrounding fuel to cool it. And the pump make take in contaminants from the bottom of the tank that can damage it or the rest of the fuel system.

Q: Will I get more gas by filling up early in the morning when it’s cooler?

A: Gas station storage tanks are buried underground to help insulate them and keep the fuel temperature relatively constant. According to the API, gasoline expands about 1 per cent for every 8 degrees Celsius and “the benefits, if any, of filling up in the morning versus the evening would be hard to notice.”

Also, gas pump meters are “volume corrected” to compensate for temperature.

Q: Why do stations post gas prices in fractions of a cent?

A: Historians at the API report that this originally came about as a way for discount gas stations opening in the 1930s to emphasize their price discount on large signs out front.

Posting prices at intervals of one-tenth of a cent is now standard industry practice. Studies show that a price differential of just two-tenths of a cent is enough to affect drivers’ choice of station.

This information is courtesy of the Canadian Petroleum Products Institute and the American Petroleum Institute.

Email your non-mechanical questions to Eric Lai at wheels@thestar.ca. Due to the volume of mail, personal replies cannot be provided

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