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I’m considering replacing my older Toyota RAV4 with a RAV4 Prime. With hybrids, if I’m primarily making short trips in the city and running in EV mode. Is there a risk that the gasoline in the tank will degrade over time?

– Melanie

Gasoline doesn’t come with a best-before date, but it’s still got a shelf life.

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Gas can start to break down after three to six months – and that could cause your car to break down.

“We see it in our fleet vehicles that get used for four months and then sit parked for eight months,” said Steve Elder, an automotive instructor at the British Columbia Institute of Technology (BCIT). “All the high-end additives evaporate out of the fuel and leave behind a varnish on the valves.”

As gas gets old and evaporates, it becomes thicker and less combustible. In your car, that might mean rough idling, a check-engine light or even a total failure to start.

“We’ve had the valves seize up in some of our vehicles, although that shouldn’t be a problem in an engine with bigger valves, like a Chevy V8 – they’ll run on anything,” Elder said.

If you bought gas from a station that doesn’t see a lot of business, it might have already been sitting in their storage tank for a month or longer before you put it in your car.

A problem in PHEVs?

So if you’ve got a plug-in hybrid (PHEV), which has a bigger battery than a traditional hybrids and lets you drive about 25 km or more on battery power, should you worry about gas going stale?

It depends. Some hybrids, such as the $199,700 Karma Revero GT, which has a reported 98 km of electric range, let you drive without using gasoline at all.

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But on most others, including the RAV4 Prime, which has 68 km of electric range, the gas engine will kick in if you press hard on the accelerator or if you’re going up a hill.

Most people will use at least some gasoline in a PHEV, Elder said.

“With the RAV4 Prime, I don’t think that’s a problem for most people because you’ll end up running the engine anyway,” said Steve Elder, an automotive instructor at the British Columbia Institute of Technology (BCIT). “If you only ever go back and forth to the grocery store, it’s possible that the engine may not start.”

Some PHEVs – including the Chevy Volt, which GM stopped making in 2019 – sense when gas is stale and will run the engine instead of the battery to burn gas, Elder said. The RAV4 Prime doesn’t do this.

The RAV4 Prime’s driver’s manual states “fuel may remain in the tank for a long time and undergo changes in quality depending on how the vehicle is used.”

Toyota recommends adding at least 20 litres of gasoline every 12 months. If fresh gasoline hasn’t been added in a while, the main display will flash a message telling you to add fuel.

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Toyota said stale gasoline isn’t usually an issue in regular hybrids, such as the Prius or RAV4 Hybrid, because they can only be driven in EV-only modes for short distances – sometimes for less than a block.

Ethanol dilemma

Filling up the tank adds fresh gasoline to the stale gasoline, but it also leaves less room for water condensation, which can make gas break down even faster, Consumer Reports said.

You can also add fuel stabilizer, which makes gas last longer, to a tank of fresh gas. It can’t reverse the degradation process, but it can slow it down.

“We use one called Sta-Bil,” Elder said. “Once you pour it in, you have to drive the vehicle so the gas sloshes around and it can mix in.”

But Elder’s biggest tip? Use a premium gasoline that doesn’t contain ethanol.

“We found one from Chevron here that has no ethanol,” Elder said. “When we put that in our fleet vehicles, we don’t have a problem,”

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While Natural Resources Canada (NRCAN) said all gasoline can degrade over time, whether or not it has ethanol, Elder finds that gasoline containing ethanol degrades faster.

Although diesel can last up to a year before going stale, pure ethanol evaporates faster and can get stale in less than a month, J.D. Power said.

Chances are the gas you’re buying contains ethanol. It’s added to make the gas greener. That’s because ethanol is renewable – unlike fossil fuels, which we’ll run out of eventually – and the crops grown to make it absorb CO2.

Since 2010, Ottawa has required that companies sell gasoline with at least 5 per cent ethanol, on average. There’s an exemption in the Atlantic provinces, the territories and Northern Quebec. Ontario, Manitoba, Saskatchewan, Alberta and British Columbia have their own rules and require gas to be anywhere from 5 to 10 per cent ethanol.

While the maximum amount of ethanol allowed in regular gasoline is 15 per cent, the average gasoline blend contains 6 to 7 per cent, NRCAN said.

Several companies, including Shell and Canadian Tire, advertise ethanol-free premium gasoline.

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It’s usually their top-tier gasoline, so you’ll have to pay anywhere from 20 to 30 cents a litre extra for it.

Have a driving question? Send it to globedrive@globeandmail.com and put ‘Driving Concerns’ in your subject line. Emails without the correct subject line may not be answered. Canada’s a big place, so let us know where you are so we can find the answer for your city and province.

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