Plug-in Hybrids and Range-Extended EVs Need To Keep Your Fuel Fresh – Here’s How They Do It

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You won’t need fuel stabilizer in your next plug-in hybrid electric car’s gas tank. Here’s why.

Here and there across America, and in decent numbers in California, many green vehicle owners now drive plug-in hybrids and electric cars like the Chevy Volt with onboard gasoline engines or gasoline range extenders that help their cars go farther once the EV charge runs out. As it turns out, many of those owners use their vehicle as an EV almost all of the time. That means the gasoline could sit in the tank for months at a time.


2018 Chrysler Pacifica Hybrid

One CarTalk Community member is typical of this growing population of green vehicle drivers.  Member Sisyphus1 recently asked for help from the many mechanics and vehicle experts in the Community who offer sage advice. Sisyphus1 has only been using about a pint of gasoline every 500 miles or so traveled in a new Chrysler Pacifica Hybrid. The Pacifica Hybrid is a Plug-in electric hybrid vehicle. It can travel 33 miles on batteries alone. With one tank of gas possibly lasting a full year or more, this owner posed the question, “Should I use a stabilization additive with my gasoline?” That is a logical question, but as it turns out, automakers thought of this too. After all, they are not keen on the idea of flocks of vehicle owners showing up on flatbeds with fuel systems plugged with sludge.

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There are a few key ways automakers manage this issue, but one solution has a simple premise; “Burn it” in the engine.  Automakers use an algorithm to determine the age of the gasoline on board and periodically instruct the vehicle to use it up. In the case of the Chevy Volt, Jon Stec, Chevrolet fuel system integration engineer, says that if a Volt owner relies on the vehicle to consume the aging fuel it doesn’t add up to very much waste.

Stec says, “For the driver who starts the year with a full tank of 9.3 gallons and runs 15,000 miles on electricity, the maintenance mode will use just enough gas to average a very respectable 1,613 miles per gallon.” And more importantly, will keep the gas fresh by periodically burning up the old stuff in the tank avoids any gas-related mischief. Chrysler employs this same type of system to burn enough gas to keep the fuel stable, and told BestRide, “If needed, the Pacifica Hybrid will automatically shift from electric to hybrid mode to cycle through any fuel that is more than 90 days old, eliminating the need to add a fuel stabilizer – meaning customers have one less thing to think about.”

Running gasoline engines also helps keep the lubrication system happy. Oil needs to be circulated and condensation in the engine needs to be eliminated by the heat and flow of the oil. Running the engine to keep the gas fresh achieves this.

Automakers have also thought about evaporation. In most vehicles, the fuel tank is made from formed plastic and works with a carbon system to manage the vaporization of the fuel. This is done mostly as an environmental protection issue. However, in vehicles like the Volt and Pacifica which may not run the gas engine often, that fuel may sit so long that vaporization could cause problems in the remaining fuel. To deal with this issue, Chevy constructed the tank of the Volt from steel and created a closed-loop pressurized fuel system to eliminate vaporization. Any pressurized vessel needs to have a way to relieve pressure, so Chevy engineers included a 3.5 psi positive pressure relief valve and a vacuum relief that opens at -2.3 psi, levels that Chevy says are rarely exceeded.

Plug-in hybrid and extended range vehicles have been selling at rates equal to or greater than battery electric vehicles as the green vehicle market expands. Going forward, more and more vehicles will use gasoline as a range-extending tool, more than a primary power source. Many plug-in hybrids are now available for sale used. Methods like these will ensure that owners of new or used green cars don’t need to worry about the hassles of adding in fuel system stabilizers to keep their vehicles healthy.