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Due to environmental considerations, I am planning to purchase a plug-in hybrid electric vehicle when the vehicle I want becomes available (RAV4 Prime). However, I am concerned of the gasoline in the tank going stale. I have the possibility to charge the car at both home and work. So, given the 60 kilometer range, I don't believe I have to drive on gasoline except perhaps two times per year. I mainly do short trips.

I'm worried of two things:

  1. If the car always prefers electricity given enough charge in the battery, I can end up having the same gas in the gas tank for a year or two. I have understood that gas eventually goes stale.

  2. If the car has a system to automatically use some amount of gas occasionally, even if you always charge the car, the gasoline consumption can actually be pretty high, so the car doesn't deliver the gasoline usage savings I'm expecting. Example: 56 liter tank, 2 month turnaround, 336 liters / year used (ok, I guess that's better than 1300 liters / year I'm currently using).

Are my worries real? How do plug-in hybrid electric vehicles handle gas going stale in the gas tank? How quickly does the gas actually go stale?

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This is what the Prius plug-in manual says:

Notice about fuel

●For plug-in hybrid vehicles, fuel may remain in the tank for a long time and undergo changes in quality depending on the how the vehicle is used. Refuel at least 5.3 gal.(20 L, 4.4 Imp.gal.) of fuel every 12 months (refuel a total of at least 5.3 gal. [20 L, 4.4 Imp.gal.] over a 12-month period), as this may affect components of the fuel system or the gasoline engine.

●If the vehicle has not been refueled for a certain amount of time and it is possible that the quality of the fuel remaining in the tank has changed, “No new fuel has been added recently. Please refuel” is displayed on the multiinformation display when the power switch is turned to ON mode. If the message is displayed, refuel the vehicle immediately

And also:

The fuel tank of your vehicle has a special structure, which requires a reduction in fuel tank pressure before refueling. After the opener switch has been pressed, it will take several seconds until the vehicle is ready for refueling.

So I assume the combination of a pressurized fuel tank and forcefully using 20 liters of fuel per year ensure the fuel stays fresh. Thus, my worries seems not a real problem: the fuel stays fresh, and the fuel consumption can be extraordinarily low.

Link to the manual: https://www.toyota.com/t3Portal/document/om-s/OM47A88U/pdf/OM47A88U.pdf

Some proposed strategies mentioned in comments to further improve gas longevity:

  • Use fuel stabilizer along with regular fuel.
  • Use small engine gasoline which apparently from Neste (Neste PRO small engine gasoline) is compatible with engines requiring as high as 98 octane fuel. It will cost at least twice of what regular gasoline costs, but two times a small number is still a small number.
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    if you are particularly concerned about useful fuel in the tank and the dealer or manufacturer does not recommend against it, consider a fuel stabilizer, commonly used for generators. I've had a three-year-stored generator fire on the second pull with Stabil, one brand of stabilizer.
    – fred_dot_u
    Dec 13, 2019 at 22:37
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    @fred_dot_u That's a very valid comment. I tried to search the linked manual for recommendation against using a fuel additive / stabilizer and found no such recommendation against using it. So I guess I could use the stabilizer.
    – juhist
    Dec 13, 2019 at 22:40
  • If I were using a hybrid under the conditions you're talking about, I'd definitely use fuel stabilizer. No sense in crudding up your injectors/fuel pump/filter because you don't. From my point of view, there'd be no down side to doing so.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 13, 2019 at 22:47
  • Another idea: I could use "small engine gasoline" which has twice the costs when compared to regular gasoline. I understand the "small engine gasoline" should stay fresh for years. Link: neste.com/benefits-small-engine-gasoline -- although I'm not sure if it has the required octane rating.
    – juhist
    Dec 13, 2019 at 22:55

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