Hydraulic oil – ISO AW 46 or multi-grade ISO AW 32/46/68.
If it’s a diesel engine it has a fuel injection pump/governor assembly. These are normally driven from the accessory gear train on the front of the engine. How about a picture of the left side of the engine?
I have a Foton 404. The Fotons work best in all temps with aw32 hydraulic fluid. My steering is two hydraulic cylinders and I use the aw32 in the steering resevoir and the injector pump. I use 80/90 weight gear oil.