An oil's properties are improved with "additives." But what are they? Monarchi, like all oil chemists I've talked to, declined to identify the few additives actually used, but did reveal their purpose in the brew. Additives for detergency help oil dispose of deposits created during the combustion cycle. Other elixirs add corrosion protection and some adjust viscosity, a property of lubricity required by say, an outboard motor running full speed in 100-degree weather. Additives for extra lubricity protect against piston scuffing, and yet others improve engine performance by keeping the exhaust system clear of restriction caused by deposits.