Mixing detergent and mineral oils can lead to engine damage. A low viscosity oil may be used in cold climates and a high viscosity oil may be used in hot climates, but oil grades should never be mixed. Jet oil should not be used in piston engines.

Since oil seeps slowly through the small crankpin clearances before it is sprayed on the cylinder walls, considerable time is required for enough oil to reach the cylinder walls, especially on a cold day when the oil is more sluggish. This is one of the chief reasons for preheating the engine or diluting the engine oil with gasoline for cold weather starting.