For high speed marine craft and railway applications higher quality oils are required. Refer to manufacturer
b.
Alternative viscosities: Ambient air temperatures above 35°C or raw/seawater above 25°C, SAE 40; ambient air temperatures above 4°C or raw/seawater below 25°C, SAE 30; ambient air temperatures -6°C to 4°C SAE 20W-20 (except Deltic)