What are Symptoms bad gas in tank?

Answer 1

The vehicle will be running poorly or down on power for no apparent reason. The fuel will be contaminated from the internal rust building up over time since gasoline is acidic and eats away at the metal. The best way to tell is to physically remove the tank and inspect the internal surface for obvious rust and corrosion. This is very true of a vehicle has been sitting for long periods of time and especially if no additives were added to preserve the fuel. A quick way if the vehicle is carbureted is to remove the fuel line and attempt brief bumps of the starter to push some fuel thru the pump to drain into a clear container for inspection. Option two is to inspect the fuel filter if it is fuel injected.