Fuel and oil additives aren't miracle cures, but they do work when used correctly. Fuel additives keep injectors clean, prevent carbon buildup on valves, and improve combustion in engines that regularly run on short trips.

Oil additives reinforce or compensate for properties of the engine oil: they inhibit oxidation, reduce friction, or seal minor leaks. Always use them within the dosage the manufacturer specifies, too much disrupts the chemical balance of the oil.