Cat 426 Hydraulic Oil Change Purge

Since i am doing the fuel tank and the hoe is down i thought i would just go ahead and change the hydraulic oil. I thought it was just a matter of pulling the plug and draining it all out and then refill the tank with 21 gallons of fresh IOS 32 oil. But, i soon realized that there will be a considerable amount of fluid left in the CYLINDERS.
So question is, how do i get all the old fluid out of those cylinders? I don't want to leave the old fluid in there as that kinda defeats the oil change theory.
All ideas are much appreciated.

Pull all the cylinders apart and repack them. Then drain the tank.

It isn't just the cylinders. ALL of the lines need to be flushed to.
Here is a link to a thread that describes in detail how to do it.
https://www.heavyequipmentforums.com/threads/best-way-to-flush-a-hydraulic-system.20793/#post-262665

unless it's contaminated with metal, or water, or a completely unsuitable oil, I'd just change the filter and drain the tank, refill. And do it again at the suggested interval.

Thanks for all the tips. There is nothing wrong with the fluid in it now, it is probably very old and that is why i wanted to change it. I never thought about it being this difficult until i decided to do it then and realized there is a LOT of fluid in each of those cylinders. I believe i will just drain out what i can, loosen the hoses on all the cylinders and let them gravity drain and refill. The current fluid is fairly clear and has no color to it at all.

edgephoto said:

Pull all the cylinders apart and repack them. Then drain the tank.

Click to expand...

Now you are talking work. lol

Tinkerer said:

It isn't just the cylinders. ALL of the lines need to be flushed to.
Here is a link to a thread that describes in detail how to do it.
https://www.heavyequipmentforums.com/threads/best-way-to-flush-a-hydraulic-system.20793/#post-262665

Click to expand...

WOW, i did look and that is also lots of work. I did notice that in the cases cited each one had a contamination problem, which mine does not. So maybe i can skip some of the extreme procedures.

Delmer said:

unless it's contaminated with metal, or water, or a completely unsuitable oil, I'd just change the filter and drain the tank, refill. And do it again at the suggested interval.

Click to expand...

Yes, i think this is my best route. My fluid is clear and smells good, not burnt. I just wanted to change it .

Aside from draining the cylinders, some of them you can shut the machine off with the loader in the air, then drain the fluid and filter, then lower the bucket, then the loader boom, and similar with the backhoe to get more fluid out. IF you do any extra draining like that to let air into the cylinders, then you have to work the cylinders at idle very little bits each direction a little more each time to try to work the air out without ever reaching the end of the stroke on any cylinder. The air can diesel inside the cylinders, and you'd be better off leaving the fluid in, or doing it the hard way with new fluid pushing everything out if you diesel a cylinder and destroy the seals.

If it is just a maintenance oil change, don't fret getting every drop out. I would drain the tank for an extended period of time...leave the plug out for a couple of days, if the machine is down anyhow. What I would do, is look to see if there is a suction screen/filter in the tank and clean that, or replace if it is not reusable. If the suction strainer is plugged it will, over time cause you problems. And, since you are draining the system it is a perfect time to make sure it is good to go.