JD 440 (GM 2-53)

[JD440ICD2006]

DELO 100 40wt is the correct oil for the GM 2 cycle, 2 stroke diesels. This is Chevron's brand, and as you state other companies have a similar oil.
(CF-2)

[tuney443]

Or 30 wt. depending on the ambient temperatures.You certainly wouldn't want 40 wt.when it's 30* or lower outside.

[JD440ICD2006]

Good point!
The Detroit mechanics tell me that 40 wt is good for engines with "time" on them and as long as it is not very cold weather.
Specs do call for 30 wt on new engines. It actually calls for lighter weights with colder temps, but we do not get that cold here very often. Since there is no cab on mine, I do not run it when it is very cold.
But they also state that the most important point is to use the Delo 100 (or equivalent rated CF-2) and ONLY a single weight oil.