Kioti DK-45 Hydraulic fluid Air bubbles

[bonz]

We have a 2001 DK-45 tractor that has air bubbles in the fluid when checked at the dipstick, they start off large and then become smaller, more "foamy". I have changed all the suction side, o-rings, filter, and rubber hose connecting the two suction hard lines. I cleaned everything and checked for leaks, i can't see any fluid leaks.

The tractor has 270 hrs, when we bought it, now it has 460 hrs. We had the "stealer" do a service when we bought it. They changed the hydraulic fluid and filter, they gave us a sample of the old fluid, it was pretty greenish, brown nasty stuff. since then we bought a backhoe, which we have used quite a bit, in hard conditions in the middle of summer. A few times we had the hydraulic temperature warning light come on, if it did, we stopped and let the tractor cool down until the next day. We thought it was low on fluid so we added some, but now I realize it was on a slight hillside, and we overfilled it. I started noticing the foaming when i was working it up at the neighbors and it shuttered (cavitation) while using the loader.
Any help on this would be very appreciated, I think it might be the pump. I do hear a slight whine, but it could be normal, never paid much attention to it.

 

[J_J]

Cavitation will cause bubbles. That is probably the sound you hear when the valve is relieving.

Install a 3000 psi pressure gage and use it to monitor and trouble shoot the hyd system.

 

[dfkrug]

I have changed all the suction side, o-rings, filter, and rubber hose connecting
the two suction hard lines. I cleaned everything and checked for leaks, i can't see any fluid leaks.

The suction side of the pump would be my first suspect, after making sure the fluid is not low. You
are checking the right stuff.

My Kioti is not the same as yours, but I do notice that I can starve the pump inlet when using the
backhoe on a steep slope. When you entrain a little air, fluid heating can be quite rapid and take
a while to clear out. Hope that's it.

 

[J_J]

You will not see a small suction leak as the leak is air getting into the fluid by suction.

You could smear some grease over the suction hoses and fittings and observe the results in the hyd tank.