Carver Owners Forum

I have twin 5.7 litre merc cruiser engines. Thunderbolt ignition. I bought the boat used and the former owner who had it for 18 years has always used 30W non-detergent oil on the engines. Mechanic recommendations are 25W40. Does anybody know if there would be any issues with switching to the 25W40 oil now?

Ask Mercury in Fon du Lac on current thinking on weight.
That's your very best answer.

Go with Merc 25W40. No problem with switching over.