I have this car im working on for a friend. It'* a 93 Buick Centry with a 3.3 V6. When she got it, it would run until you got to about a 1/2 tank then wouldn't run anymore until you put more gas in. At first i thought the gauge was bad, (its had the pump replace already), when me and my dad were towing it home we stopped and topped it off and it started right up. This leads us to believe there is ALOT of water in the gas. It has sat for many years, even before she got it. Can i just burn out the old gas with some octane boost then put some HEET in there then fill it up with some fresh gas, or do i need to drop the tank, drain it and so on? I really don't want to drop the tank.