I have a Nightster, I was reading in my owners manual about the oil and it says if you can't find Harley oil then use a diesel rated oil. I use Rotella 15W-40 in my diesel truck and I am wondering if this would be fine to use in my bike? I pretty much think the Harley oil is a gimmick, i'm sure it's fine oil and everything but I know there are lots of others out there that are just as good or superior. 15W-40 is just a little thinner than 20W-50 but I live at 8000 feet elevation so the hottest it gets up here is about 90. Usually only in the 80's.

 

Ask your dealer first.

 

15-40 ROtella has a LOT of detergent additives in it.

 

I would only use it if the temp. was below 80. If you want use 1 oil in both vehicles you could go with regular auto Mobil 1 15w-50.