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I never thought I would have to ask this but so far I have put 475 miles using almost all EV.
Is it good for the gas to stay in the tank indefinitely or should I let it go down?
Loving my 2018 Clarity!
 

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2018 PHEV Touring Atlanta, GA
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I never thought I would have to ask this but so far I have put 475 miles using almost all EV.
Is it good for the gas to stay in the tank indefinitely or should I let it go down?
Loving my 2018 Clarity!
It's really no different a question than if someone has a second (or third) car that is rarely used. If you search online you will find a wide range of opinions on how long you should keep gas in the tank in those situations. Some people say no more than a month or two. However many Clarity owners have gone a year on the same tank of gas with no apparent problems. However the key word is "apparent". Some problems would be readily obvious, like rough idle, problems starting, etc. However other problems like corrosion caused by moisture may not become noticeable until the car is say ten or fifteen years old. If you are the cautious type I would say try and go through a tank of gas every couple of months. However if you are the "if it ain't broke don't fix it" type try going for a year like some people do. Or maybe something in between like six months.

A related topic is how often the gas engine should be run. Again many opinions on this as it relates to cars that are not used very often. Some say run the engine once a week, some say once a month. When the Clarity starts the engine it will idle through warmup then shut off if not needed. Some people feel that you should run it longer than that so that moisture can be burned out of the oil, and so that the higher pressures of acceleration can blow off carbon. Other people say that's all nonsense for a modern car with pressurized fuel tanks burning fuel with modern additives.

Maybe this isn't an answer, but at least it's some things to think about. You can do some research online, but again I think you will just find a lot of different opinions with no actual proof given to support any of them.

Some people add fuel stabilizer, but in my opinion that makes sense more for something like a lawnmower that will be sitting through winter, or a backup generator where it's not convenient to run it every few weeks. But in our case we just barely have to lift a finger and press the HV button to give our engines a workout and burn some fuel.
 

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I burn the gas out after a year. This is in-line with what my Chevy Volt will do.
 
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I burn the gas out after a year. This is in-line with what my Chevy Volt will do.
That is an interesting data point, as it gives some indication what GM engineers thought about it, at least for the Volt. From what I have read there will first be messages appearing on the screen encouraging the owner to let EV miles go to zero and burn some gas. At some point if the suggestions are ignored it will start burning gas on its own. Not sure if it's based solely on the calendar or if it is also measuring any other parameters. Could be that it is partially based on how the engine performs during the Volt's version of the Clarity "System Check" every few weeks.

I found an old article from 2014 quoting a GM spokesperson, not sure if this applies to Gen2 Volt also.

"If a driver always commutes in all-electric mode, the engine maintenance mode will activate after five to six weeks, and there is a fuel maintenance mode that runs every nine months to a year, according to a G.M. spokesman, Shad Balch."

I thought I read that Chevy does not recommend E85 in the Volt, if so then I would think the maintenance mode schedule assumes that the correct fuel is being used.
 

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That is an interesting data point, as it gives some indication what GM engineers thought about it, at least for the Volt. From what I have read there will first be messages appearing on the screen encouraging the owner to let EV miles go to zero and burn some gas. At some point if the suggestions are ignored it will start burning gas on its own. Not sure if it's based solely on the calendar or if it is also measuring any other parameters. Could be that it is partially based on how the engine performs during the Volt's version of the Clarity "System Check" every few weeks.

I found an old article from 2014 quoting a GM spokesperson, not sure if this applies to Gen2 Volt also.

"If a driver always commutes in all-electric mode, the engine maintenance mode will activate after five to six weeks, and there is a fuel maintenance mode that runs every nine months to a year, according to a G.M. spokesman, Shad Balch."

I thought I read that Chevy does not recommend E85 in the Volt, if so then I would think the maintenance mode schedule assumes that the correct fuel is being used.
Per my owner's manual, E85 is fine. Engine maintenance mode (EMM) occurs every six weeks if you don't get the engine hot enough to fully activate the catalytic converter and EGR system. Fuel maintenance mode (FMM) occurs when the average age of the gas in the tank reaches one year. Also, Chevy recommends against fuel stabilizer additives.
 
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