IH HyTran was developed having no zinc. Zinc is an inexpensive anti-wear additive used in many hydraulic fluids. Caterpillar, for instance specified minimum 900 ppm zinc. Interchange is going to contaminate one. The old tale was detergent engine oils would foam in a hydraulic system and cause failures. What about engines then with all the high speed parts? Cat specifies 15W-40 engine oil in hydraulic systems used in the Middle East where temps can exceed 50C or like 122F. Cat tractors is a broad statement because Original Challengers were Cat design. Cat Challengers with tractor size rear wheels were build for Cat by New Holland and so were basically New Holland tractors with Cat running gear so fluids would be what the Canadian New Holland plant used.
