As long as your car is running properly, you’ll usually have no need for fuel or oil additives. In fact, almost all gasoline and oil you put in your car already has added detergents and other additives. One additive that may be useful if there’s moisture in your car’s fuel system is dry gas or methyl alcohol. Dry gas makes it easier for the moisture to burn off once it reaches the combustion cylinders. Another problem that can sometimes be helped by a fuel additive is excessive knocking. If your car knocks upon acceleration, you may not be using a high enough octane-rated gas. If you’re already using the highest-rated octane gas and the problem persists, octane booster may help. If your car has a large number of miles and smokes from the exhaust, an oil additive may help. A mechanic or clerk from your local auto parts store may be able to help you with any further questions you may have about fuel and oil additives.