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'Tis the season for winter gasoline

Just as the weather changes from summer to winter, so does gasoline. Stations are now selling winter gas, specially blended for the season.

“Winter gas can have a higher RVP, or Reid Vapor Pressure,” says Wayne Moorehead, marketing manager for Canadian Tire Petroleum. “That is a measurement of the volatility of the fuel, and how subject it is to evaporation. In winter, you want a fuel that has higher volatility, because it’s easier for the vehicle to start.”

But there’s more to it than that, and it comes down to government-mandated emissions standards. There are several places where gasoline vapours can enter the atmosphere: at the station when you’re filling up, out of the filler neck if your gas cap isn’t tight, and possibly out of the tailpipe, if small amounts of unburned fuel make their way back there.

Gasoline evaporates faster when the outside temperature is hot. A fuel with lower RVP—one that’s refined specifically to evaporate more slowly—is less likely to send harmful emissions into the air, and so the mandated standards require refineries to make lower-RVP fuel for sale during the summer months.

However, lower-RVP fuel requires a different refining process. It’s costlier to make, and Moorehead says it’s tougher to produce the large quantities of fuel needed in winter. Since gasoline naturally evaporates more slowly at cold temperatures, the emissions standards allow for higher-RVP fuel to be sold in the winter.

When it’s cold out, some drivers worry about their fuel freezing up. However, it’s far less of a problem now that cars have fuel injection, rather than carburetors, which were far more likely to experience issues with their fuel lines icing up.

Keeping your fuel tank full will help prevent water in the gas, which is the stuff that freezes. “Drive on the top half of the tank, not the bottom half,” Moorehead says.

“A fuller tank has less area for condensation to take place, and having more fuel will spread out any water that is in there. People should also make sure the fuel cap fits properly, too. If you have a loose cap and it’s not sealed properly, there’s an opportunity for moisture to get in.”

That full tank could also help ensure your safety. Cars generally get poorer mileage in the winter, and if the weather turns bad or traffic backs up, your commute could take much longer than normal. If your tank is close to empty, you could run out of gas and be left stranded.

Tips

• Manual. Go by the octane recommendation in your owner’s manual. If you only need 87-octane regular fuel, there’s no need to use premium.

• Location, location. Be smart when fuel-shopping. You’ll burn up a few cents difference if the cheaper station is far away, or there’s a long line at the pumps.

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