Whoa! 20w50 is not the oil of choice for a Jinma steering system. The manual, and the Jinma dealers I know, recommend using AW-32 hydraulic oil and nothing else. Deviate from that at your own risk.
Is the squeaking noise coming form the pump, the steering motor, the priority valve (if so equipped) or is it a mechanical squeak from something rubbing? A hydraulic pump that is stalling (pumping against excess back pressure) will make a noise that I'd call "whining", while a relief valve that is opening makes a noise that is what I'd call a "groaning" sound. High p[itched squeaking noises are usually from friction - rubbing, dragging, scraping, etc.