Hello all. Do someone here know Hitachi hydraulic pump gearbox system. When i fill it with oil to the max on stick the gearbox puke up 150 - 200 ml thru the ventilation cap. I have been using it like it is but It is annoing because there is no oil on the dipstick. I am using 80w-90 gear oil on the gearbox. No leaks Or anything The dipstick on pics are not original but it is right. Am i using wrong oil?
I'd fill the gearbox to the full mark then run it until it stops leaking then drain the oil to confirm how much oil remains in the box. If there's sufficient oil in there then run it with 200mils less oil. The only places oil can enter the box during operation is the engine rear main seal or the pumps input shaft seals. An oil analysis would confirm whether it's engine or hydraulic oil if in fact the gearbox oil level is increasing while operating.