15W-40 is a very common viscosity grade for diesel engine oil. GTX Diesel is a 15W-40 diesel engine oil formulated to help extend engine life.
If you need a 15W-40 diesel oil, Castrol® GTX® Diesel helps extend engine life, protecting against the wear and tear of severe weather, rough roads and heavy tows. As a 15W-40 viscosity grade, it flows like a 15 weight oil from start up in Winter, but provides the protection of a 40 weight once the engine reaches full operating temperature.
When your owner's manual calls for 15W-40 diesel oil, Castrol® GTX® Diesel has the ability to extend your diesel engine's life in a variety of applications and duty cycles. It provides superior protection, conforms to the strict requirements of PC-11 engine oil technology and can be used in diesel engines where API CK-4, CJ-4 and below is required.