Castrol GTX is one of the world's most trusted engine oils. It's more than just oil. It's liquid engineering that protects against the problems your engine faces every day. Severe driving conditions can cause the build-up of a thick, tar-like substance called sludge. Sludge can block your engines vital oilways like cholesterol and if untreated, it can rob an engine of power, and ultimately, its life. Castrol GTX Double Action formula cleans away old sludge**, and protects against new sludge formation better than tough industry standards. Help extend the life of your engine with Castrol GTX. **When tested in engines with high levels of deposits.