Examining used hydro fluid

[MESSMAKER]

When you change your oil, you can tell a difference between the used oil and new oil. I don,t really see the difference when changing hydo fluid. It is the same viscosity,color and looks nearly the same. Is it the same for you guys?

 

[Gary Fowler]

Yep. Just like new when drained. As long as it isn't contaminated with water, I think just changing the filter would suffice BUT (big but) oil is fairly cheap and not worth the risk of not changing it at recommended intervals.

 

[TractorGuy]

I have never changed the hydraulic fluid in my John Deere. I have changed the filter once and added some fluid. It remains clear and I see no reason to change it.

My backhoe had condensation get in the fluid once and has had a couple of major leaks that resulted in having to change the fluid. One time when it had water in it due to a missing cap gasket the fluid was fairly new. I saved all the old fluid and let it sit a few months then pumped the good fluid off the top for reuse. Last time I changed ALL the filters and made sure ALL the seals were good and it hasn't ever been milky again.

 

[DieselBound]

Doesn't hydraulic fluid suffer from viscosity breakdown?

I'd also worry about all the particles/contaminants that are smaller than can be filtered end up building within the fluid. The concern would be that this would tend to make up a greater, albeit small, percentage of the fluid: it's possible that it could also bond, which would then get collected up by the filter(s) (requiring a more frequent filter change interval- some filters aren't cheap!).

If one could get by with just filter changes I'd think that the big players might be pitching this practice to their big high-end machinery customers as that would be a huge savings (one could, perhaps, and maybe they already do this, have live/running filter switching like I believe already exists with fuel filters and(?) oil filters?- I could probably Google it!).

 

[EarPlug]

This looks like a good source of info

The Seven Most Common Hydraulic Equipment Mistakes

 

[Texasmark]

I have never changed the hydraulic fluid in my John Deere. I have changed the filter once and added some fluid. It remains clear and I see no reason to change it.

My backhoe had condensation get in the fluid once and has had a couple of major leaks that resulted in having to change the fluid. One time when it had water in it due to a missing cap gasket the fluid was fairly new. I saved all the old fluid and let it sit a few months then pumped the good fluid off the top for reuse. Last time I changed ALL the filters and made sure ALL the seals were good and it hasn't ever been milky again.

Slightly off topic but same result with motor oil. I had a covered pan of it sitting back on a shelf for quite awhile. Oil went in black but when I recovered it from the shelf, the oil was clear and all the contaminants were on the bottom. Found that interesting. Don't know how long it took. Don't know the contaminants left in the oil....sulphuric acid maybe to name one possiblity.

 

[mcfarmall]

Slightly off topic but same result with motor oil. I had a covered pan of it sitting back on a shelf for quite awhile. Oil went in black but when I recovered it from the shelf, the oil was clear and all the contaminants were on the bottom. Found that interesting. Don't know how long it took. Don't know the contaminants left in the oil....sulphuric acid maybe to name one possiblity.

A detergent style motor oil contains additives that grab on to contaminants and keep them in suspension. Perhaps the used oil that was sitting on the shelf for a long time was non-detergent oil and after enough time the contaminants settled out?

Back to the original topic, hydraulic oils contain additive packages that become depleted over time. The oil looks fine and perhaps nice and clean but doesn't provide the anti-wear and anti-foaming properties that it did when it was new.

 

[redman135]

I was told that the main reason that you change your hydraulic oil is because the additives wear out or are used up, not because the oil wore out.
At one time you could get additive packs (to replace the old additives) to add to your oil without doing an actual oil change.
I don't know if you still can or not.

 

[newbury]

This looks like a good source of info

The Seven Most Common Hydraulic Equipment Mistakes

From that:

The only way to know when the oil needs to be changed is through oil analysis.

If the cost of analysis is a lot less than the cost of a change get an analysis.

Example:
My F350 requires about 15 quarts for an engine oil change. "Recommended" every 3,000 to 5,000 miles. Using Rotella T6 I went over 18,000 miles with good UOA's.

 

[Texasmark]

A detergent style motor oil contains additives that grab on to contaminants and keep them in suspension. Perhaps the used oil that was sitting on the shelf for a long time was non-detergent oil and after enough time the contaminants settled out?

Back to the original topic, hydraulic oils contain additive packages that become depleted over time. The oil looks fine and perhaps nice and clean but doesn't provide the anti-wear and anti-foaming properties that it did when it was new.

Nope. Quality detergent oil, may have been some of the synthetic I use in most of my stuff. I was surprised. Course "held in suspension" has it's limitations with gravity being what it is over time.