My old V8s 3.5rrc 3.9rrc ran on 20w50 never had an issue, and they ran like swiss watches.
my other engines 2.25 and 2.6 engines ran on SAE 50 without issue
The current tow pig 4.6 rr p38 runs on shell 10w40, changed every 5k.
my old vm ran on anything i had lying around in my shed usually a...