Hydrocruiser

There are now many dual rated oils...both diesel and gasoline..yes they are good. Rotella Synthetic..Mobil-1 DelVac 5W-40 for trucks/suvs etc.

Good stuff and great for boats in the 15W-40 formulations.

gsmith9898

which is better in a boat. mobile 1 ep or rotella synthetic or mobile 1 delvac?

Hydrocruiser

I believe the DelVac and Rotella-T synthetics are 5W-40's. They would be better off in a towing vehicle with that weight.
API CI-4 PLUS, CI-4, CH-4, CG-4, CF-4, CF
API SL, SJ, SH

Note the DelVac and Rotella T synthetic also carry the API SL rating...so it is intended for use in heavy loaded gasoline applications too..not only diesel.

The Mobil-1 15W-50 EP is a great choice for a boat.

The Rotella and other conventional diesel/auto rated oils in the 15W-40 weight are good choices.