Castrol GTX Diesel is engineered to clean away and protect against harmful diesel engine deposits. (API CI-4/SL) Application Castrol GTX Diesel 15W-40 is suitable for use in automotive diesel engines including inter-cooled and turbo-charged engines where the manufacturer recommends an API CI -4 or earlier specification 15W-40 lubricant. It may also be used in gasoline engines where the manufacturer recommends an API SL or earlier Specifications. Advantages Outstanding diesel engine wear protection Superior cleaning power to maintain engine performance Reduces build up of harsh deposits Helps prevent oil from thickening and keeps it flowing freely