I have read the older forums where various operators said to use SAE30 oil in their cat pumps. When I read the cat pump oil bottle it says ISO68 "petroleum-based , hydraulic oil with advanced additive package to protect against wear, oxidation, rust and corrosion" So why wouldn't you just use ISO68 hydraulic oil? Am I missing something here? ISO68 oil is 20 weight oil to begin with not 30 weight. Not sure what the difference is between motor oil and hydraulic oil though. I thought hydraulic oil was designed not to mix with water and to let it settle to the bottom of the hydraulic tank which is what I would think you would want with a cat pump as well.