Oil capacity varies by variant: 34 L (6BTAA-5.9-G2), 21.4 L (6BTAA5.9-G13), 16.4 L (6BTAA5.9-G3). The Cummins/Onan 6BTAA5.9 engine line groups 9 variant designations. Parts and fitment are pooled here so a cross-reference found on one variant surfaces for the whole family.
| Variant | Displacement | Cylinders | Rated rpm | Oil capacity | Coolant |
|---|---|---|---|---|---|
| 6BTAA-5.9-G2 | 5.9 L | 6 | 1,500 | 34 L (35.9 qt) | 23 L |
| 6BTAA5.9-G13 | 5.9 L | — | 1,500 | 21.4 L (22.6 qt) | 26 L |
| 6BTAA5.9-G3 | 5.9 L | 6 | 1,500 | 16.4 L (17.3 qt) | 26 L |
| 6BTAA5.9-G5 | 5.9 L | — | 1,500 | — | — |
Each figure is from that variant’s own documents (see its engine page for sources). Oil capacity can differ between applications of the same engine; check the manual for your generator set.