AeroShell Piston Engine Oil 100, a straight mineral oil, is made from carefully selected high viscosity index base stocks. It contains no additives, except a small amount of pour point depressant to improve fluidity at low temperatures and an antioxidant. This oil is mainly used during the break-in process of new or recently overhauled four-stroke aviation piston engines. Break-in duration and lubrication guidelines vary, so operators should consult the engine manufacturer or overhaul facility for specific recommendations.