If you put sugar in a gas tank, it wont destroy the engine, but it can cause problems by clogging up the cars filtration system. Sugar does not dissolve in gasoline, so it will sink to the bottom of the gas tank and settle there. If there is too much sugar, it can clog the fuel injectors or the fuel filter, which might make it necessary to replace the fuel filter or even empty out the gas tank. However, sugar wont turn into a semisolid, gooey substance that totally clogs up the gas tank, fuel lines, and so on, as some rumors suggest. If you suspect someone has put sugar in your gas tank, its best to take your car to a mechanic to have it inspected and cleaned out.