Burn Auto > Cars > Parts > Motor Oil > Castrol GTX Diesel 15W-40 Castrol GTX Diesel 15W-40 Castrol® GTX® Diesel 15W-40 is designed to help your engine run more efficiently and extend engine life. https://www.castrol.com/en_us/united-states/motor-oil/conventional-motor-oil/gtx-diesel-motor-oil.html