The 8921 uses 6.7 gal. (23 liters) Silicone Oil, part number 5-1070-x.
Depending on availability, you can order the silicone oil coolant in a variety of sizes:
|Part Number of Silicone Oil||Container Size|
For convenience, Bird offers various maintenance kits for the 8920 series that includes the silicone oil here: 8920 Series Repair & Maintenance Kits.
Please see the Material Safety Data Sheet (SDS) for further information: Silicone Oil SDS