When you shut off your engine, the oil on the cylinder walls drains back into the crankcase. Also, any residual gasoline in the combustion chamber either evaporates, leaving carbon deposits. This results in what is called dry starts and accounts for most of the engine wear. Using Marvel Mystery Oil leaves a thin layer of oil in the combustion chamber and cylinder walls which reduces or eliminates dry starts. Also, the thin layer of MMO in the combustion chamber prevents the formation of hard, baked on carbon deposits.