Hydraulic oil viscosity

[Yooper]

I noticed that my stump grinder loses a fair amount of power as the oil gets hotter. I'm seeing oil temperatures between 130-140 degrees F. I'm using AW 46 and was wondering if went to 68 (or higher?) if that would help. When the oil is cold, say sixty degrees, the pressure gauge will show 50 psi when free wheeling. After the oil warms up, it shows zero. This leads me to believe the oil is 'bypassing' in the motor.

Just an FYI, the hydraulic oil is only being used to power the grinding wheel. Not used in any of the controls. The pump is a Prince PTO gear type. Motor is a DMC from Surplus Center, not sure if it is a gear or vane type. Both have less than 25 hours.

 

[North Idaho Wolfman]

You could try bumping it up or better yet try motor oil, older bobcat's use motor oil for hydraulics because it doesn't thin out as easy under temp for running the drive motors.

 

[Yooper]

That's interesting! Did they use a straight weight or a multi viscosity?

 

[D2Cat]

It's multi viscosity. I think you can use the same oil as the engine.

I'm working on an early '80's bobcat 825, made by Clark back then I think.

Manual says use their hydraulic/hydrostatic transmission fluid or 10W-30 or 10W-40motor oil API Class SE or SF can also be used.

(this critter takes 27 GALLONS)

 

[boz1989]

Our case skid steer uses 10w30 motor oil. I believe that there is an anti foaming agent that is recommend to add to it. I would have to find the bottle to be sure.

Sent from my LGMS330 using Tapatalk

 

[amsoilman]

Send me a PM and I will give you some resources to help you out there

 

[Yooper]

I'm going to give the motor oil a try. AW46 is equal to 10 weight according to my research. 10w-30 should be a good choice. Oils with an API rating have anti foaming additives in them, so I should be good there. The diesel rated oils seem to stress this point, so maybe I should consider that? I've learned this much, researching oil is complicated!

 

[Yooper]

Update: I replaced the AW 46 with some 15W-40 diesel rated oil. It did help a bit, but not as much as I was hoping for. I think my expectations were a little too high.

 

[North Idaho Wolfman]

Sadly it's sounding like you have an issue with either the pump or the motor.
how do pressures look?

If the motor, pump, and valve are both good, then might need more cooling or maybe run 80W 90 in it.

 

[clay45]

I use 20w-50 conventional motor oil in my SCAG zeroturn mower hydraulics. They caution you to NOT use synthetic or any special energy conserving oil as its not beneficial to the hydraulic system. Naturally the hydraulic oil filter is a motoroil filter. And an annual change of "hydraulic" oil and filter perks it up. I'm a Pennzoil guy in the crankcase but I used Fred's 20W-50 (Warren oil) in my hydraulics last year and it worked great. I'll do same this year.

 

[Yooper]

Sadly it's sounding like you have an issue with either the pump or the motor.
how do pressures look?

If the motor, pump, and valve are both good, then might need more cooling or maybe run 80W 90 in it.

A cooler might be in the works. When I ground stumps this weekend, the air temperature was in the mid 70's. Oil got to 150 degrees on Sunday after pushing it hard all day.

Today the air temperature was in the mid 40's. Oil got to only 115 degrees and the grinder was working noticeably better. Going to start doing some research.