I've had a Komatsu D65P-8 for a few years now for some bush and farm work. I had always been using regular tractor trans-hydraulic fluid in the hydraulic tank. I finally got a manual for the machine and I see they recommend 15W40 in the engine AND in the hydraulic tank. I'm replacing all the filters and some of the fluids in the machine this summer. My question is, should I drain the hydraulic tank and replace it with all 15W40? or will it be fine as a blend of 15W40 and hytran?
The Komatsu experts will be able to advise you further but if KM are anything like Cat they went through a "one size fits all" phase regarding lubricants. The idea being to reduce the different oils a customer had to keep in stock. With Cat that methodology has now gone by the board and lubricants are specified by type based on the system in which the oil is being used. So hydraulic systems get hydraulic oil, etc. Personally I would say you are fine to continue using what you're using right now in the hydraulic tank.
What he said^^
I looked if I could use a single oil across my machines including wheel tractors ,4x4 and Mitsubishi truck . My dozers have two grades ,recommended 15w40 in motor, hydraulics, finale drives and winch with Castrol offroad transmax 30 in the transmission , Komatsu recommend a different oil in the transmission for a reason , which is a bit odd considering the winch has clutch packs not much different to the transmission yet uses 15w40 . In the finales I use 80w90 . It won't be much different in the price between hydraulic and 15w40 so using whats recommended next oil change must be best . I'm not keen on running two different oils together . Cold or hot temperature operation recommendations will be different across the machine to .