For partial fill-ups (a few ounces or less) use SAE 140, SAE 85W-140 or SAE 80W-90 weight gear oil with an API rating of GL-4 or GL-5. For full replacement use SAE 140 or SAE 85W-140 gear oil with an API rating of GL-4 only.

We also found that 80W-90 oil with an API rating of GL-1 is acceptable for both partial and full replacement of tiller gear oils.