Castrol GTX 20W-50 is an API SN/CF mineral engine oil designed to clean away old sludge* and protect against new sludge formation better at a rate that exceeds industry standards. Severe driving conditions like those found within major cities can cause the build up of the thick, tar-like substance. Sludge can block your engine’s vital oil galleries like cholesterol in an artery– and if untreated it can rob an engine of power and in severe cases can cause catastrophic engine failure. Help extend the