Duragard Diamond Synthetic CK-4 SAE 5W-40 - 5 Gallon Pail - Meets Ford WSS-M2C171-F1 Exceeds warranty requirements of engine manufacturers that require a type API CK-4/SM premium 100% synthetic SAE 5W-40 motor oil. (HTHS) High-temperature, High-shear viscosity. Excellent oxidation protection for hotter, heavy duty engines Meets Fords stringent 2017 and newer WSS-M2C171-F1 & prior specification. Backwards compatible for all engines currently requiring CJ-4