What oil do you recommend?

[Amkeer]

I use Mobil 1 in my Mercury Outboard. It gets used, cleaned, and then put in the shop. I change it once a year.

 

[Peted]

Quicksilver 25W-40 is one of the best oils on the market - period. For any full load or HD application it is superior to many automotive oils. Does not shear down as quick as many automotive oils...

Gets used in race engines, motorcycles, and LOTs of boats, worldwide. It's my go-to oil for flat tappet breakin's and most high output street engines, now that I can no longer get Delo 400 SD (severe duty).

I'd use it in that motor in a heart beat. Unless the rings or the valve seals are bad, the CAT's will never see enough oil to matter. We ran HDEO's in gas trucks with CAT's for decades and as long as the motors are in good shape the CAT's don't fail. Once the rings start to go, the CAT's ash cap before they fail from Phosphorus "poisoning". Just not a real worry.

From my extensive research for the best Marine engine oil, whether old school engine block or higher end Yamaha 300s then QuickSilver 25w40 is the go to lubricant. Amazing stuff. I use it in my 2006 Yamaha F250s, Motors run great