NOTE: The Environmental Protection Agency (EPA), through the Clean Air Act, has required that detergent additives, also referred to as Deposit Control Additives (DCAs) be added to all gasoline from January 1, 1995.
Practically as important as octane rating and volatility are the additives that refiners put into their gasoline. Carburetor/Fuel injection detergent additives help clean the tiny passages in the carburetor or fuel injectors, ensuring consistent fuel/air mixtures necessary for smooth running and good gas mileage. Other additives are used to help control combustion chamber deposits, gum formation, rust, and wear. One additive you may have noticed in your vehicle is manganese. Since the advent of the catalytic converter and the resultant widespread use of unleaded gas, manganese has been used in many fuels as an anti-knock additive in unleaded gasoline. Manganese works, but it leaves reddish deposits on spark plugs. So, if you pull your spark plugs and notice that they are covered with what looks like rust, don't panic. It's only manganese and it's as harmless as the lead deposits it replaces.