You mean, a hydraulic fluid?
There are hundreds of them, depending on the desired properties. They are difficult to develop, because some drawbacks must be addressed precisely. Like: wetting ability, defoaming, corrosion protection, viscosity index, behaviour under extreme load, and so on.
So just trying quickly won't work. This is a hard process.
Vegetable oils are a decent start. At least, they lubricate and don't corrode, and they are biodegradable. They serve (with additives!) in forestry machines.