What causes hydraulic oil to go black

[ROAMER_AUS]

Hi all,

Customer has some hydraulic hoses to be made. Hoses inside had oil in them but black as used engine oil almost. He mentioned that he was aware of that and can't find a solution and if I could look into it. Fiat Cobelco 16 ton. Don' know model yet. He says that they changed the oil, but it turned black again.
Now what causes hydrauilc oil to go black usually? Honestly, I've never seen it before.

Thanks!!!

 

[grandpa]

Pull a sample and send it off. Takes the guess work out.

 

[Tinkerer]

Is cross contamination with the engine oil a possibility ?

 

[Vetech63]

Draining and replacing the hydraulic fluid only gets you so far, it still leaves oil in all the function cylinders and hoses. As soon as you fire it up and work a few functions, the black oil left in the machine will turn your new oil black also. You would have to do oil changes several times to get even close to clearing that up, but you have to know what is causing the black oil and repair that issue first.

 

[Chrisso]

A good question to ask is "are any oil levels rising/dropping noticeably?" If so, that's definitely a problem.

 

[Kobelco ireland]

Take a sample and send it off to make sure no one poured in anything that should not be there. How many hours are on the machine and has the hydraulic oil ever been changed before. Hydraulic oil should be changed ever 2000 hours but is nearly always over looked by customers or there reply is "i put 5 gallons of new oil into it after it burst a hose three years ago" lol. Also check both finals to see if there are full of hydraulic oil, I have seen drive motor seal go a few times and final drive fills with hydraulic oil and the dirty gear oil gets flushed back through hyd system

 

[Randy88]

Is there any sort of hydraulic lock brake in the system somewhere that could have been dragging causing it to burn, or clutch packs?? Whats the history of the machine? owned it forever or just purchased it and only put a few hours on it? Engine and hydraulic oil coolers in the same unit?

I agree with the others, oil sample it and then go looking when you know for sure whats in the oil to give it a black color

 

[ROAMER_AUS]

Thank you all for your inputs! I'll pay attention to it all and report back!

 

[Nige]

Ask the customer does the black oil have a burned smell, or any other type of smell for that matter.?
Also ask them what brand & viscosity grade of oil they are using.

 

[d9gdon]

My guess is from cross contamination with engine oil, most likely from a hydraulic pump driven off the engine that has a failed seal in it.

 

[BSAA65LB]

Some cylinder/center swivel seals will cause oil to start turning black as the seals start to fail.