Yamaha SHO Oil

The ONLY oil I've found that prevents "making oil" in my 4.2 F300s is Amsoil 10w40 marine. Have tried many others, and all result in significant fuel dilution.
 
I did the song and dance of searching for a higher quality oil/better price oil for my 250 Sho last year.
I found all kinds of people with f-series motors on offshore rigs running Rotella. There's a bunch running various pcmo as well with no issues.

The thing is, those guys use of a motor is completely different from what a SHO's typical life is on a bass boat. They'll cruise around 4500 rpm for an hour or 2, troll for 4-8hrs then cruise back. Oil is allowed to get up to temp and stay there for hours on end, rpms not too high, and during the season they're ran daily.

A typical sho will sit for a week, 2 weeks, a month, get fired up to idle for a few minutes then hammered to 6k for a couple of minutes and shut down. Repeat, repeat, repeat all day. The oil very rarely makes it to operating temperature. That type of use is brutal on an engine and oil.

I'm much easier on mine than most by letting it warm up before getting on plane, gradually increasing rpm as the temperature comes up, and letting it idle to bring the temp down before shutdown, but I still would never trust a pcmo to protect it.
T6 is out also. The F series motors are spec'd to run 40 weight oils, the sho is not. 5 or 10w30 is all the book specs. Could you run thicker oil? Probably in warm climates, but I wouldn't.

The yamalube is no doubt overpriced, but it's not a bad oil. I really like the big shot of moly in it and the zddp is pretty decent. I will however be giving amsoil a shot when I change it this year. It's pretty much the same price as the yamalube synthetic. If I can't get something I trust for cheaper, I can at least try a perceived higher quality oil for the same price. I'm going to send out uoa on the yamalube, and a voa for the amsoil when I do the change. More than likely, I will get a uoa around the 25hr mark to check up on how the amsoil is doing then a final uoa at next year's drain to compare.
 
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