Hydraulic Drive Oil Cooling Fan System Hydrapak. Hydraulic oil cooling package. It includes the oil reservoir, cooler, return line filter and system relief valve. All components are designed into a small, lightweight and quiet.10GA, 316 stainless steel mainframe, reservoir 14 GA, 316 stainless steel double wall construction integral diffuser eleminates foaming and vortexing. Heavy duty, corrosion resistant, high efficiency oil cooler. Hydraulic motor driven fan is factory set for optimum performance. Standard spin on filter with 10-micron element. Cartridge style relief valve. Auxiliary tank access for case drain port. 4 (1/4″) SAE gauge port.