ZD331 Oil Capacity Guide
Direct answer and scope
The Kubota ZD331 zero-turn mower diesel engine typically takes about 3.7 US quarts, or roughly 3.5 liters, of engine oil when the filter is also changed. The commonly cited service fill is 3.6 to 3.8 US quarts depending on whether the filter is included and how completely the oil drains. This figure applies to the standard ZD331 model with its Kubota diesel engine.
What the capacity covers
The oil capacity is for the engine crankcase only. It does not include the hydraulic or transmission system, which uses a separate fluid and has its own service interval. When refilling after an oil change, owners should add slightly less than the full listed amount, then check the dipstick and top up gradually to the full mark.
Filter and drain considerations
The stated capacity assumes a standard oil filter replacement. If the oil is changed without replacing the filter, the required amount may be slightly lower because residual oil remains in the old filter. Conversely, a completely dry engine or one that has been apart may require a small additional amount beyond the normal service fill.
Practical fill note
Use a diesel-rated engine oil that meets Kubota's specification for the ZD331. The owner's manual is the authoritative source for the exact viscosity and API classification for the expected operating temperature range. After refilling, run the engine briefly, shut it down, wait a minute, and recheck the dipstick on level ground.