That is one of the things that too many don't understand about some engines especially the Detroits. There are so many options available for them no one answer can be considered right for another engine.It could be any number of different oil pans. Hopefully you have a dipstick? I'd guess somewhere between 3 and 5 gallons.
I'm going to play Devils advocate here so take it as you will. I have built numerous detroits over the years and have always used Rotella T 15W40 in all of them.
I run a collection of detroits , 353 471 671 s . They are all getting on on years now but i have always ran them on straight 40 as recomended with good results. Most of mine are in cranes which really is a bad application for them so they slobber a lot. I have always run mine at the half level on the dipstick which keeps reduce the mess from slobbering down .
In Kens post it is specifically stating not to use the multi viscosity oil in marine engine builds. This is due to the continuous load marine engines have, those builds even have special oil control rings for marine applications. I realize I am in the minority here but I always stay with what has worked the best for me through experience. Count me as one of those old dogs that can’t learn this new trickI'll play, I realize the delo is a little harder to find and you have to order it some places. But with the price the same, why wouldn't you just get the straight 40 wt. that they formulate just for the 2 strokes?
I pulled a pair of 16v-92's that had been in a big boat, and they always ran the 40wt. As do most of the big boats running 2 stroke, and those engines run and run and run and run.
From Chevron about Delo 100:
Applications
Delo 100 Motor Oil is recommended for use in two- and four-stroke diesel engines in farm machinery, construction equipment, marine, and other off-highway
applications where SAE 40 grade is specified by the OEM. Delo 100 Motor Oil is recommended for use in two-stroke diesel engines requiring highly effective
control of wear and deposits. Delo 100 Motor Oil utilizes exceptional quality technology to provide excellent performance in older engines burning ultra low sulfur
diesel fuels. Delo 100 Motor Oil meets the requirements of:
• API Service Categories
— CF†, CF-2†
• Detroit Diesel Corporation two-stroke engine
recommendations, including the 0.85% ash
maximum limit for Series 149 engines.