Sierra 25W-40 4-Stroke Synthetic Catalyst-Compatible Marine Oil This Sierra Synthetic Blend Engine Oil meets modern recreational 4-stroke engines with or without emission catalyst systems. Features Minimizes corrosion that is formed inside the engine. Displays enhanced detergent properties to suspend and prevent engine sludge formation. Industry leading wear protection and deposit control. Prevents excessive thinning under extreme performance operations. Capitalizing on ZDDP anti-wear additive t