The 8251 uses 1.1 gal. (4.1 liters) Silicone Oil. The Bird part number is 5-1070-2.
For convenience, Bird offers various maintenance kits for the 8251 load that includes the silicone oil here: 8251 Repair & Maintenance Kits
Depending on availability, you can order the oil coolant in a variety of sizes:
|Part Number of Silicone Oil||Container Size|
Please see the Material Safety Data Sheet (SDS) for further information: Silicone Oil SDS