It can be difficult to tell if your gas has been siphoned. The best way to tell is to keep track of your fuel level before you leave your car and make sure the level hasn’t changed when you return. If you do have a locking gas cap, there might be scratches or damage on it where thieves attempted to access your gas.
Is 2 year old gas still good?
However, gas that is more than two month old is generally OK to use with only minor decreases in performance. Gas that is older than a year can cause issues, like engine knocking, sputtering and clogged injectors. Bad gas can be drained from the tank to prevent damage to the engine.
