Mercruiser 454 Carb engines

[tonyiiiafl]

On my 1994 390 I have the port engine which is original at 1180 hours, Starboard 3 years old at 125 hours. I have been using Quicksilver 25W40 oil and same filters, Quicksilver. What is the opinion of switching to the 25W40 synthetic blend? I don’t run hard if that matters, but those girls are pushing a lot of boat.

[Viper]

Really comes down to how much you run the engines IMO. If you only require one oil change annually, then I say mineral oil is fine unless the engine specifically requires otherwise. The synthetics remain more stable longer, so if you boat year round and wanted to stretch out that oil change interval, then go synthetic. Since we're in northern climes, and the recommendation is to change the oil prior to every winter layup even if there was little use, then mineral oil will do IMO.

[tonyiiiafl]

Thank you. That confirmed my opinion also.