Hi Robb,
Castrol did/do make a range of excellent Heavy Diesel engine lubricants that are market specific (Country of engine origin mainly)
I believe that only one is a "full" synthetic like Delvac 1 5w-40 and this a Euro engine only product
I assisted in the development of their first semi-synthetic 15w-40 HDEO for American diesel engines commencing around 1991-2. It ("Enduro LD" LD = Long Drain) was an excellent product - it has been renamed and updated twice since 1997
It is possible that the Belgium made 5w-40 could be used in heavy engines (especially if Euro sourced and under 10ltr) but it really depends on the engine/oil specifications
Since the BP buyout of Castrol many engine lubricants are now cross marketed and BP had a full US spec. synthetic 5w-40 HDEO at one stage
I would not use any oil in a Heavy Diesel engine that did not meet the engine maker's stated specification. I have seen too many problems (sludge/rapid piston/valve train wear/combustion chamber deposits/high oil consumption) caused by such action
Regards
Doug
