M59 hydraulics got slow and weak.

[rScotty]

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.
SNIP
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.

Yes, the directional levers sure caught me out.

Good point about heat being due to how hard the machine is being loaded. At first I didn't see how Kubota could anticipate load. Then as I read through the workshop manual on their flow tests I see that they do the hydraulic flow test by setting at 2000/2200 RPM, loading the system until a specified minimum temperature is achieved, then remove the load and go to full RPM. Then load it again for a pressure test. I thought I'd seen warnings on max temperature, but today I only see the standard range (104 to 140 F)

The tests are very exact for flow rate and pressure. It does take a couple of special tools and a workshop manual, but given those things Kubota has made it easy to verify if the system is operating as designed.

Not having the special tools and all, I did a "cowboy" version of the flow tests by warming the machine up with no load and then timing the backhoe loader cycle times with a stop watch. Near as I could measure, mine came out right at factory spec. I timed it at full rated RPM - that being how I interpret the info on pg 7 of the backhoe manual.
rScotty

 

[TBarD]

I thought I'd seen warnings on max temperature, but today I only see the standard range (104 to 140 F).
<snip>
I timed it at full rated RPM - that being how I interpret the info onl.pg 7 of the backhoe manual
rScotty

So far as I have been able to determine from standard hydraulics resources, oxidation of a typical oil starts to increase dramatically around 150 (probably depends somewhat on the specific formulation and additives). Around 180 rubber seals such as in cylinders and valves begin to degrade. The viscosity of oil decreases with temperature, again depending upon the formulation - multi-viscosity oils have a wider range of useful temperature. Lubrication decreases if the oil is too hot/thin (low viscosity), increasing pump wear, and the oil is more prone to leak past the pump gears, valves and seals, decreasing system efficiency and enhancing heat generation. Lower viscosity decreases the chance of air entrainment due to vacuum (e.g. in a cold start), but the capacity of the oil to hold dissolved air decreases with temperature, which will increase the chance of air entrainment due to dissolved air coming out of solution. Air entrainment if severe enough can cause cavitation (superheating of air bubbles as they are compressed in the hydraulic pump), which is very damaging to the hydraulics, and can destroy a hydraulic pump.

The bottom line is, performance will depend upon the characteristics of the hydraulic oil, how the system is designed, e.g. reservoir capacity and design, suction design, etc., and how it is used. The best oil to use could vary depending upon usage, e.g., cold temperature use in the winter vs summer use working the system hard. The top of the line, expensive hydraulic oils we use are presumably good all purpose multi-viscosity oils, although it is very hard to get specs. If you have an unusual use, such as running the system hard in high temperatures, a different (higher viscosity) oil might be more appropriate.

So far as hydraulic oil temperature goes, a good rule of thumb is probably 1) anything up to 140 F is safe, 2) start being concerned at 150 or above, 3) try to not exceed 172 or so, consider backing off, 4) at 180 slow it down, stop, or fix the problem, unless you really know the system and what it is capable of or only plan to work at this level for a short time. At least, this appears to be the general recommendation for hydraulic systems. I note this is similar to what is recommended for the AT in my truck. Yes it can survive a higher temperature for a time, but it will shorten the life of the transmission. These systems are not that different.

> pg 7 of the backhoe manual...

Whoa, is there a backhoe manual for the M59? I could not find one hence have been using the one for the L39. There probably isn't much difference, but it would be good to get the specific manual if there is a part number.

 

[lhansman]

Hi TbarD

The manuals that came with my L45 cover both the L45 and the M59. The L39 and the M59 were out before the L45 so early M59's may have come with a combined L39/M59 manual but I'm just guessing.

Regards,

Lauren

 

[rScotty]

> pg 7 of the backhoe manual...

Whoa, is there a backhoe manual for the M59? I could not find one hence have been using the one for the L39. There probably isn't much difference, but it would be good to get the specific manual if there is a part number.

In 2008 my M59 came with the operator's manual for the tractor and loader as well as a backhoe manual. Both were slightly soggy from being in that leaky plastic manual holder behind the seat. The backhoe manual is for the Kubota Backhoe model BT1200 - which is the M59 backhoe. The manual is 21 pages, the format is like the operator's manual. On page 2 it says "Note: the specifications are taken with the Kubota M59 tractor".
I thought everyone got one of these. Page 3 of the specifications has the cycle times I've been referring to. Also lots of other interesting info.
rScotty

 

[indianaEPH]

I was operting the back hoe yesterday pulling out stumps. This is fairly demanding work on the BH with a lot of stalling of the BH and going to pressure relief. IT was a cool day about 60F. I measure the sump hyd fluid temperature after running at 2000rpm for about an hour. It was 120f. I measure it at 2700rpm. After an hour it was 123F. Cooling system is working well

 

[Hersheyfarm]

I took my infrared temp gun and checked my hydrualics friday. Outside where about 78 degree. The engine block itself hits close to 200, so shooting the front pump was worthless, it came in at about 180.

Now the transmission mounted pump reaches 160, as does the tranny case that is mounted to the motor. The return line going to front pump got about 145-150. The back boom cylinder reached 145-ish. these temps are running at 2600.

IndianaEPH, How did you take fluid temp? I didn't draw any fluid out so all my reading are from surface temps.

 

[indianaEPH]

Hersey:

I have a thermocouple temp measurement. I stuck the wire (on a stick) into the sump from the back filler. So I was sure it reached the fluid when I did it(It was dripping). I dont have an infrared meter so I could not do surface temps very well. I would expect the sump to be generally less than the return line because it is cooling in the sump prior to getting sucked into the pump for another round through the circuit. I think 145 from the return line may be an OK reading (not too hot).

 

[TBarD]

Hersey:

I have a thermocouple temp measurement. I stuck the wire (on a stick) into the sump from the back filler. So I was sure it reached the fluid when I did it(It was dripping). I dont have an infrared meter so I could not do surface temps very well. I would expect the sump to be generally less than the return line because it is cooling in the sump prior to getting sucked into the pump for another round through the circuit. I think 145 from the return line may be an OK reading (not too hot).

Removing the fill/vent cover and pointing an IR gun in should also work well to measure the fluid temp in the reservoir, it seems like it is a straight shot. These temps sound normal to me. I'll try to take some measures on my M59 in a week or so when I get back to work with the tractor.

 

[TBarD]

I finally got a chance to check the hydraulic fluid temperature, after working the backhoe for a few hours peeling a bank back. I have an excavation with a cut 6-7 feet high, vertical, at the back where it cuts into the hill (nothing is flat around here). The job was to slope it back 12' or so above the 4' level. Anyway, a lot of typical backhoe work, a lot of cylinder action and fluid motion. The ambient temperature was about 65. After 90 min or so at a moderate level (2K RPM) I measured 140 at multiple spots with the IR gun. The temp down the fill hole was not appreciably different than the reservoir housing or the pump end of the main hydraulic pump. I increased the RPMs to 2.2K and ran hard for another couple of hours, after which the temps averaged about 158 measured a multiple locations. This is higher than I am used to but I was working it harder at a higher RPM than usual (I did not want to go any harder as I was on the edge of a 7' vertical cut and anyway this was precision work trying to get a level surface). I could not test the in/out temps of the oil cooler as they are not easy to get to while the engine covers are on. My feeling is that these are normal temps when working hard for hours - they are not much different than my truck AT when driving unloaded. At no point was there any issue with performance or power.

 

[indianaEPH]

that sounds like a lot more work <time> than when i measured the sump temp. I will retest after longer operation.