Originally posted by SteveS
Not to go off onto a different tangent, but Mobil Delvac is designed for commercial diesel engines, not gasoline engines. Diesel and gasoline engines have different needs when it comes to an oils chemistry, etc. So while it won't necessarily harm your engine, it won't provide all you are probably expecting.
Mobil is now repackaging their Delvac 1 as M1 Truck and SUV formula 5w40, so they seem to think it works in gas engines.
The Delvac 1 will last longer each interval it is used. I would suggest going 3 intervals of 6,000 before doing a UOA and determining OCI.