Why not Zeng?
CD is an old Diesel engine oil classification.
TO-4 might pass CE,CF,SA, SB, SC, and maybe SD.
That brings us up to 1972 is spark, and later in Compression ignition.
A little bit of history .....
a )API CD motor oil specifications were introduced into markets in the States in 1955 (MIL-L-2104C/D) for use in (Naturally Aspirated;Supercharges or Turbo) diesel engines.
b )After which Caterpillar adopted Shear-Stable (powershift) Transmission Oil Specifications in TO-2 (in year 19xx,anybody?) whose approved list includes only Monograde SAE 10W/30/40/50 SAE CD Motor Oils, not multigrade SAE CD if it existed (since year 19xx,anybody).
c )Then comes SAE CE motor oil specs in 1983 (MIL-L-2104D/E) whose Monogrades are similarly approved to Shear-Stable TO-2 specs.
d )In 1989, SAE CF-4 motor oil specs was introduced only in multigrades form , no monogrades were included.
Therefore there wasn't any TO-2 approval for any CF-4 motor oils due to non-compliance of TO-2's requirement of Shear-Stability.
e )Meanwhile, in mainly overcoming short wear life of powershift transmission friction clutch discs with use of TO-2/SAE CD and SAE CE monogrades oils ....
then comes a new superceding specs in Shear-Stable TDTO TO-4 of viscosity grades SAE 10W/30/40 and SAE 50.
No motor oils in any SAE Cx class were ever
approved to TDTO TO-4 specifications.
f )These Transmission Drive Train Oil (TDTO) TO-4 are gear train oils and replaces TO-2 in gear train systems and this TO-4 does NOT replace the so-called TO-2 in engine crankcase which belongs to SAE CD/CE monogrades or CF-4 multigrades.
The TO-4 oils are NOT motor engine oils (which falls under SAE CD/CE and CF-4 then).
Hence my remarks in all my previous postings above and other threads as well.
Just my 2 cents.