Castrol GTX Ultraclean is our cleanest GTX ever. The unique Double Action formula cleans away old sludge* and protects against new sludge formation giving you more control over today's environmental challenges. The modern world creates difficult challenges for engines. Poor fuel quality, heat and tough driving conditions can all lead to sludge that potentially shortens engine life. Sludge is a sticky deposit that builds up in an engine's oil-ways and it can prevent the oil from protecting the engine. Provides superior protection in gasoline direct injection engines (including but not limited to GDI, FSI, SIDI, EcoBoost – check your owner’s manual for details). *When tested in engines with high level of sludge