Reply With QuoteSounds weird, but Engine oil is one of those things everyone seems to have an opinion about. I have been using full synthetic oil in my last 3 boats for over 12 years. My old 21' Daycruiser with the 350 King Cobra is still going strong (sold it to my neighbor across the street) with over 1200 hours on the engine.
Mercruiser used to recommend a single weight 30 or 40 weight oil. It seems when they went to EFI they also got the engines running a bit warmer than they did when they had Carbs. I think that is when they went to the 25w 40 oil.
I used the Mercruiser oil on my Eliminator Eagle 300 XP with twin 502 Mag MPIs until the original factory warranty was up. Then I switched to Full Synthetic oil. Switching to the synthetic oil reaaaaly quieted the valves and lifters.
I have read quite a few articles in Powerboat, Poker Runs America, and ***boat... and the consensus among the writers was the synthetic was a better option.
It does not create sludge in the engine like conventional oils and is significantly slicker, resulting in a measurable increase in HP. Just how much that increase is seems to be debatable. As I recall, Teague said in excess of 10%, but I have read other places as little as 4%. Regardless you should notice it.
Now it is a good idea according to all I have read to stay with either a 20w-50 or 15w-50 synthetic oil. Lower weights are not recommended in anything I have seen.
I have tried Amsoil, Red Line, Castrol Syntec and Mobil 1 Supersyn. I have settled on Mobil 1 supersyn 15w 50 as the best bang for the buck. Amsoil and Red Line cost 2x what Mobil 1 does.
I now use that in my Ultra 21'LX with the 350 Mag package. It purrs...
I have since been corrected, I think it may have been Tyler Crockett in Powerboat that gave that 10% figure. Teague likes single weight oils.
