Castrol Transmax Offroad 50 Engine Oil 20L Castrol GTX is one of the worlds most trusted engine oils. The modern world creates difficult challenges for engines. Poor fuel quality, heat and frequent short trips can all lead to sludge that potentially shortens engine life. Sludge is a sticky deposit that can block your engines vital oilways and if untreated it can rob an engine of power and, ultimately, its life. Castrol GTX with 3X CLEAN formula works to Catch - Control - Clean dirt from engine oilways, keeping your engine cleaner for longer and helping to extend engine life. Castrol GTX also protects against new sludge formation better than tough industry standards. Help extend the life of your engine with Castrol GTX.