Before assuming the worst, put a battery charger on the battery at the lowest setting for two or three hours. If it can be saved it will take up to a half hour for the acid to become conductive and the battery STARTS to take a charge.
Most people will say the gas will be stale but I have a 20-year-old fuel injected car with 4100 miles and an 80 model with a carburetor. Both currently have over five-year-old gas and both start and run fine. I'm told that is not normal. I'd try starting your engine on the gas that's in it now before automatically draining it. Even if you drain the tank, that won't get the gas out that's in the lines and injectors right now so it is still going to have to cranked on that old gas. If the tank is less than half full, consider adding some fresh gas.
My biggest concern has to do with an automatic transmission. The fluid will have drained from the clutch packs leaving the fiber plates to dry out. Front pump and clutch pack seals will also have dried out and could be brittle. Typically, if there is going to be a problem, it will shift fine at first, then develop leaks or slippage. If you don't have any transmission problems for 100 or 200 miles, you can probably stop worrying about that.
Friday, February 22nd, 2013 AT 5:43 PM