Iíll drain the oil that shipped with the engines and replace with the Shell Rotella.
I would get and read the manual and follow the break in procedure religiously. I would not change the oil they shipped the motor
with. The oil when you get it may have a higher zinc content and maybe a break in type oil. If Yanmar wanted you to change the oil before running they would tell you.
Most likely the lowest C spec listed in the Yanmar manual is CD and that is available if you go looking for it (usually as single weight SAE30).
Very true. While the manual says CD or higher is fine they state the recommended viscosity is 10w-30 or 15w-40. Finding a CD oil in multi vis may be near impossible. Rotella T6 is a CK-4 oil and the motor
he has is modern, common rail and low emission. For low sulphur fuel
like today (as opposed to high sulphur or 30 years ago) works better with higher grades than CD. Like CK-4 which is fine for the application, easily had and what the owner wants. https://dieselnet.com/tech/lube_clas...tions.php#ck-4
As they are new engines there is a warranty to consider and it would be wise to use and operate the motors exactly the way the Factory tells you. With all due respect to Mr. Bunyard I would think Yanmar would be the authority on what to use in regards to lubricants.
Don't forget to change the marine gear
oil and adjust the valves. Keep an engine
log book as it may aid in any warranty issue (save your receipts) and resale value.