I use Pennzoil 15-40 marine all year and its a CI-4, CH-4, CG-4, CF/SL oil.
I also uses it in my Dodge WC-51, GMC CCKW, Oldsmobile diesel, John Deere diesel, Yale lpg forklift, Lister diesel generator++
If the engine oil gets to 100C it will have the same viscosity as a monograde 40 oil.