Hi, I normally drive apx 13 miles a day during the week, and top off every night as recommended in the owners manual. My question is before I recharge or top off my battery each night I have a 100% full fuel tank as I should since my dealer filled up my tank prior to purchasing my Volt. In the week of ownership I have not used one drop of gas since purchase. How come when using the Onstar app on my Droid it shows a 100% full tank of gas and before plugging in later that evening (13 miles), the updated info on charge status shows 90% and 8 gallons of gas when I never use gas? Charge overnight It's back up to 100% and 9 gallons of gas. Any suggestions?

That's most likely related to ambient temperature. Gasoline expands and contracts with temperature. That's why they suggest filling up in the morning before it starts to warm up outside. You get more gas per dollar that way.

Edit: Or I suppose it's possible that it has something to do with the tank being vaccum sealed and the pumps regulating the pressure. But I'm not familiar enough with that to know if that's a possible cause. But if it's right on the cusp, I'd guess even parking on an incline or decline could affect the reading. In any case, charging has no effect on your fuel levels in any way, shape or form.

Thank you that would make sense.

I'm with dwl on this, its most likely the temperature over variables...not only feeling up in the morning is a good idea, also allow the fuel to fill slowly so as not to produce a lot of air bubbles that take up valuable fuel space....