Castrol GTX 5W-30 is a synthetic blend motor oil with a double-action formula proven to clean away sludge that can block engine oilways and help prevent new sludge formation.Sludge is a thick, tar-like substance caused by severe driving conditions such as heavy traffic, poor fuel quality, harsh driving conditions, and exceeding oil change intervals. Like cholesterol in arteries, sludge can block your engine’s vital oilways, robbing it of power and ultimately shortening its life.Tested in engines with a high level of sludge.Meets or exceeds the following specifications: API SP/SN PLUS/SN/SM, ILSAC GF-6, Meets Ford WSS-M2C946-B1, Meets Ford WSS-M2C961-A1.