Question Which oil for Cummins ISL 9 and ONAN 8K?

[Rich W.]

I just serviced mine and used Delo SDE 15w-40 which is a CK-4 oil and I think is semi synthetic, but I used it because it was on the shelf. Had Rotella too so it was a toss up, The unit just calls for 15w-40 and since it doesnt have a DOC/DPF I dont think it matters beyond that. No need for ultra low sulfur or post 2017 greenie happiness (ISO Clean, GHG17...) or whatever.