I’m flushing all the fluids in my old Hydra Mac and red fluid, assumed to be ATF, drained from my hydraulic reservoir. I was planning to replace it with ISO 46 hydraulic oil but am now concerned with any remaining ATF mixing with the ISO 46. Should I return the oil and use ATF? Perhaps ATF is better for the machine anyway. Thanks in advance.
My personal opinion would be to go with what ever oil is recommended for the machine, assuming you have something to tell you what that was!
46 is a lot heavier oil than ATF. Might be a concern.
The red fluid might just be a dye that was added to the oil. Its very unlikely that ATF was ever ran in the hydraulics, as its not very suitable for hydraulic oil. ISO 46 is likely a better oil for your machine, assuming you live in a warmer climate. As kshansen said, the best thing to do is follow manufacturers recommendations.
My Hydro Axe feller buncher has run the hydraulics and hydrostat drive system on one big single reservoir tank ATF fluid system since the late 70s. It is still just the way it came from the factory. It works well in summer and winter.
I have a galion 15 ton crane that runs ATF in it. If your current system has atf in it, I wouldn't try to change it. It will be a pain to try to completely remove it , you won't get it all out and you'll end up with a mixture. Which probably wouldn't be the end of the world, but why complicate things. I would take back the hyd. oil and buy atf.
Cat SOS might be able to tell you if it is ATF if you tell them this is what you are trying to determine.