Originally Posted by Alaskan Sea-Duction
Ok folks there may be some bad info here.
In my Cat Marine Engine (3208) and Twin Disc (MG-507) manuals it calls for certified TO-2 or C-3 test specification. TO-2 is the old spec. The replacement spec is TO-4. Again this is GEAR oil, not motor oil.
For Delco it is Delco Torqforce 30wt
For Cat it is TDTO 30wt.
Check your manuals. I can't stress that enough. Most of the spec may have been updated. Pretty simple.
Many if not most good single weight CD motor oils meet the TO-2 specification, for example Shell Rotella T1 30W or Delo 400 30W. These are marketed as a motor oil, not a gear oil. There are tractor hydraulic oils that meet TO-2/4, but are harder to find on the dock. Many oils marketed as gear oils have hypoid gear EP compounds in them, and these are specifically prohibited by TD. It is all in the manual, but proprietary oil specs can be a quagmire. There is really not a heck of a lot of difference between gear and motor oils in a 30W.
Also, true synthetic multi-vis oil may not shear easily, but what is allowed to be marketed today as "synthetic" is quite loose. Most of them are dyno oils that have been "converted" to synthetic, and the additive packages that achieve the multi-vis rating are similar.