M59 hydraulics got slow and weak.

[Hersheyfarm]

That's how we've all been taking the samples, but there's a problem with that method. By all means do the test, but until we figure this out be cautious about what you see.
When we draw a sample from the rear dip stick hole on our tractors we do it by pulling the oil up with vacuum. That lowers the pressure on the fluid substantially. Add that lower pressure to a transmission oil that is a little bit warmer from being run and maybe a little bit entrained from normal pump action and simply drawing up a sample could be enough of a pressure change to cause the normal dissolved air to come out of solution in the form of bubbles....What I'm saying is that without a doubt some part of what we are calling "entrained air" is nothing more than an artifact of how we are collecting the samples. We just don't know how much we are causing. Might be near nothing and then again it could explain it all.

Bottom line: I believe we are making a mistake. The way we are collecting the oil sample is causing some part of the bubbles which we have been calling "entrained air". We need to be drawing the samples at normal operating conditions. And not by using a vacuum or syringe.
Enjoy!
rScotty

Well since I started this.. The first time I saw this oil in this condition is when draining it into a clear jug for filter change. If your so curious try that, or take your little syringe and slurp some warm fluid up from a bucket and see what you see. If your syringe tube is bellow the surface of the fluid and doesnt itself have a "suction" leak you are getting good results.

Most equipment that works this much fluid have a large tank for hydraulic fluid storage, not just the tranny. Think about all the fluid circulating in this thing. And untill I see samples from other types of equipment this fluid could be more normal than most think. Plus the suction part of the system is in itself a large vacuume, or syringe. same physics.

 

[indianaEPH]

OK, I also checked my fluid after use. I don't have pictures but it is the same as RScottys. Before use it is clear, after use it has lots of tiny bubbles. However, The loader, transmission and back hoe all work well.

I would say that this is not evidence of an issue with Hersey's Back hoe.

 

[Hersheyfarm]

OK, I also checked my fluid after use. I don't have pictures but it is the same as RScottys. Before use it is clear, after use it has lots of tiny bubbles. However, The loader, transmission and back hoe all work well.

I would say that this is not evidence of an issue with Hersey's Back hoe.

OR its an issue with all ours...kidding(kinda)

Thanks for checking, I feel better with three of the same samples. I have raised my fluid level just to see if it helps with bubbles but no. I am now starting to think the back boom is just kinda slow compared to a full size backhoe. I'll learn to live with it. I will check my tractors fluid out of couriosity.

 

[indianaEPH]

1 other bit of information. When I took the sample with the suringe I did it very slowly. So the suction, or negative pressure, would have been very low. So I think Scotty's suction induced buddle theory is out the window..

Also, this is my fisrt BH and it does what I need it to do. Hersey may be expecting and needing more. Maybe what is acceptible to me, in terms of the boom swing speed is not enough for someone that is use to more? BTW I measured my boom swing speed and it was a bit less than 3 seconds from 90deg to center. Have you done this Hersey?

 

[TBarD]

It appears that some amount of air entrainment is normal with hydraulic systems and with the M59 in particular (according to these tests we likely see this in all cases). In hydraulic systems this is a common issue. The main reservoir is designed with this in mind, e.g., it should be large enough to allow some time for air to bubble off (and for the oil to cool), anti-foam agents are added specifically to reduce foaming resulting from this process, the return line must be below the surface to avoid agitation, the suction line must be well separated from the return and sufficiently below the surface to avoid formation of a vortex which could suck in air. The suction section must be short and without bends, clogged filters, or other obstructions to minimize a drop in pressure which would increase bubble formation. Cold temperature and increased viscosity increases suction pressure drop which makes bubble formation and cavitation more likely during startup, which is why we have multi-viscosity fluids such as SUDT2.

The amount of dissolved air a hydraulic fluid can hold decreases with higher temperature, and the pressure drop in the suction line increases with the flow rate of the hydraulic pump, at constant temperature/viscosity. The amount of heat produced increases with engine RPM and with the system load as well as with the flow rate working against obstructions in the hydraulic circuit. Open center systems run at full flow rate regardless of load so all factors leading to increased air entrainment are enhanced as engine RPM increases. The diesel engine may be able to run at max RPM all day but this does not mean that the hydraulic system can do so as well, at least not without heat buildup and increased air entrainment as a result. If the M59 produces 16 GPM at 2700 RPM it should deliver e.g. 13.6 GPM at 2300 RPM, with consequent reduced system resistance and heat buildup, and increased cool down time in the circuit.

I don't think we can rule out an air leak or other issue with HersheyFarm's M59, but it is quite possible that the machine can be worked hard enough to overheat the hydraulic system. System load, ambient temperature, or oil viscosity and formulation could all be an issue. Perhaps we should be monitoring oil temperature and maybe engine EGT, and reducing load if necessary, if we are working these machines to their maximum.

 

[indianaEPH]

Tbar

I think that your analysis makes sense.....but Kubota is not a small equipment fabricator so I find it hard to believe that they would recommend 2700 rpm if the hydraulic system can't keep up with the thermal loading. But who knows. If the oil cooler is obstructed, or slightly obstructed this could certainly push the hydraulic system over the edge, so to speak.

My oil cooler got blocked with various chaff and I had to remove it to clean it out.

I never run my machine at 2700rpm but I'll try it this week end to see if I can determine any ill effects (I doubt it because it will be in the 60s this weekend).

Hersey: Have you inspected your oil cooler? Sorry if this has been covered but I don't want to read the 15 page thread again.

 

[Hersheyfarm]

Tbar

I think that your analysis makes sense.....but Kubota is not a small equipment fabricator so I find it hard to believe that they would recommend 2700 rpm if the hydraulic system can't keep up with the thermal loading. But who knows. If the oil cooler is obstructed, or slightly obstructed this could certainly push the hydraulic system over the edge, so to speak.

My oil cooler got blocked with various chaff and I had to remove it to clean it out.

I never run my machine at 2700rpm but I'll try it this week end to see if I can determine any ill effects (I doubt it because it will be in the 60s this weekend).

Hersey: Have you inspected your oil cooler? Sorry if this has been covered but I don't want to read the 15 page thread again.

Yea its been inspected by dealer, not me. this thing was in shop hooked up to their hydraulic tester and they only found a couple of bad check valves. They even looked at the screen in sump.
Anyways I am looking in my shop manual at it says swing cylinder from 90 degree to center is 2.1 second but they dont list rpm. what was your rpms when you timed.

 

[indianaEPH]

I tested at 2500 rpm. I think they would normally check it at max RPM.

 

[TBarD]

I think that your analysis makes sense.....but Kubota is not a small equipment fabricator so I find it hard to believe that they would recommend 2700 rpm if the hydraulic system can't keep up with the thermal loading. But who knows. If the oil cooler is obstructed, or slightly obstructed this could certainly push the hydraulic system over the edge, so to speak.

It should be able to run all day at 2700 without overheating - with no load. When working the machine hard though, overheating is definitely a possibility, with any hydraulic system. Overheating is also possible if there is any leakage in the hydraulic system, e.g. a faulty valve, seal, or just too much time at relief pressure. If overheating is suspected it is easy to check with an infrared temp gun. Normal operating temp should be between about 130 and 150 max. Anything over 180 is too hot and will harm components. If the oil cooler is suspect it is easy to check with the IR gun, just measure the temp at the outlet vs the inlet to see how much cooling is being delivered. If an overheating issue is suspected it might be wise to install an oil temperature gauge or alarm.

Also, in the case of "slow and weak" don't overlook the obvious! (the directional levers used to switch between backhoe and 3pt modes). This one caught several of us out already.

 

[Hersheyfarm]

Mine is right at spec for cycle time.

Kubota told me they are ok with 180 degrees on their hydraulics systems. I have no ideal why, nobody here agrees with that. One of the pumps is bolted to the block which gets pretty hot itself. How can they cool against that? Most pump are not bolted to the block and that makes since.