From one of my Hwh documents that I have downloaded. My fluid is already red so I used the Dexron when I did some maintenance.
The fluid discussion is a relatively simply discussion. HWH recommends using only
“HWH Hydraulic Jack Oil”. Multi-purpose transmission fluid or the “Dexron” transmission fluids have been
used and are compatible with the HWH hydraulic jack oil. The advantage of the HWH oil is it is clear. This
will make clean-up from an oil leak easier. There is no dye to ruin carpet or other fabrics. All of these fluids
will mix with each other, but it is not recommended to add a red fluid to the clear HWH oil. DO NOT use
bottle jack oil, brake fluid or power steering fluid. Synthetic oils may or may not be compatible so do not use
these oils without checking compatibility.
The two main things to remember about oil are; 1. Only clean, compatible oil should be added to a system
and 2. The oils mentioned above are flammable. This is why it is critical to protect hoses and equipment
from extreme heat sources.