Under Pressure: How the Volt Stores Gasoline

It's very interesting. Often when I'm explaining to someone about how the Volt functions as an extended range electric vehicle, the questions immediate turn to the gasoline and not the electric. "How often do you use the gas?" and "What kind of mileage do you get on gas?" And of course, as soon as I mention that I haven't put gas in the car yet and don't anticipate needing to do so any time soon, "Isn't the gas going to get stale?" and "Don't you think you should run it on gas often so it doesn't ruin your engine?"

Any Volt owner who has done his or her homework knows that gas is not a big concern. The Volt was designed to be used in a lot of different ways. For the sake of argument, you could choose to never charge it and run it purely on the gas generator. But then, why buy a Volt to begin with? Many Volt drivers (perhaps the majority) make a good effort to use the Volt as an electric vehicle with a gas backup for the occasional long trip, or morning after the night where you forgot to plug in the charger (what do Nissan Leaf drivers do when this happens?). Many Volt drivers take the "gas-free lifestyle" idea seriously. Many Volt drivers can tell you how many particles they have kept from emitting into our atmosphere every time they hit the road running on electric.

So how does the Volt make this possible? Gas left in an average car would begin evaporating after a couple of days or weeks of non-use. Most modern combustion engine based cars have carbon filters built into their gas tanks to trap the fumes and return them to the gas tank the next time the car runs. This works fine when you're using gas to run your car on an almost daily basis. If you rarely use gas, you need a special gas tank. And that is absolutely what the Volt possesses.

Volt engineers and supplier Spectra Premium Inc. developed the Volt's gas tank from 1/4 mm thick hot-dipped tin-zinc coated steel to resist corrosion from both inside and out. Despite the strength of the tank, it has a mechanical pressure relief valve that begins opening at 3.5 psi and a vacuum relief that opens at -2.3 psi, levels that are rarely exceeded (Chevrolet Press Release, 3/11/2011).

Even with a tank that doesn't let humidity in or let fuel vapors out, you still need to use the gas and replenish it periodically. What does that mean in Volt terms? Every six weeks, if the integrated combustion generator hasn't been powered on, the powertrain controller sends a message to the driver letting him or her know that the engine needs to run. This is called "maintenance mode". The driver may defer maintenance for up to 24 hours at which point the gas generator will just up and run on its own to use some of the fuel and keep the internal components lubricated and fit for use.

Furthermore, if the driver goes a full year between fill-ups (and the car does knows this via the powertrain controller, more about this in a minute), then maintenance mode will kick in and and use up the old gas until and unless the driver fills up with fresh fuel to mix with the old fuel.

FYI, you're right - I totally intend to be in this maintenance mode boat at some point. Partly for the experience, but mostly because I'm using almost no gas at all.

As Chevy's fuel system integration engineer for the Volt, Jon 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."

How does the Volt know that you have not filled your tank? In the Volt, there is a gas-tank release button as in most modern automobiles. To the naked eye, it doesn't seem to operate much differently from your standard gas door release. This is what mine looks like.

When you hit the button though, the gas tank door doesn't simply open. In fact, the door is spring loaded. When you hit the button, the gas tank pressure is released so that you can open the door and unscrew the cap to add gas. It takes a few seconds and a message on the display in the cabin will let you know when you may safely remove the cover.

I haven't tried this, mind you. I'm just going by what my owner's manual tells me to do. I'm not sure how often I will do this but I gather it will be seldom and I'll need to look back at this blog to remind myself how to do it each and every time.

The cover looks like this.

So, nothing really special there. But as you've already read, there is specialness going on behind the cap.

Chevrolet recommends premium top-tier gas for the Volt. Pro drivers on the Chevy Volt Owners Facebook group also recommend ethanol-free petrol, but this seems to be not as important as the premium top-tier part. I've been scouting out top-tier ethanol-free stations in Orlando. I wish I'd known to do this when I was still driving my Camry, because I was filling it up at a different gas station almost every week. But alas... who knows when next I'll be purposefully pulling into a gas station? Maybe if I need a pack of gum or I'm hunting for the ever-elusive Pineapple Fanta.

One last photo, so you can see how it all fits together.

This is a Volt "skeleton", if you will. For reference, what you see towards the upper left corner is the FRONT of the car... in other words, what's under the hood. What you see in the back is below the rear chassis. The upside-down T shape in the middle is the 17.1 kWh battery pack (in a 2015 Volt - only 16.5 in prior year models) which sticks up into the cabin, accounting for the reason why the Volt is only a four-seater rather than five. Incidentally, my kids, Sheridan and Bryce (10 and 8, respectively), who sit in the back most of the time, consider the four-seater a definite upgrade from the five seat sedans of their past. Who wouldn't rather be in a bucket seat?

Even though the car is meant to be Sheridan's someday, Bryce wants to make sure he's hedging his bets, just in case.