Hydraulic fluid foaming?

Highbeam · Apr 22, 2009

So when I first start the machine and it is warming I will check the hydro fluid and there are no bubbles. I have to do the usual double dip to get a good reading.

Then after it is warm and being worked I will do another check and I have noticed that I find some small bubbles in the fluid. I have replaced the low hanging grey hydro filter mount twice over the years and I am having no leakage from those joints and everything on the tractor works fine.

I am most concerned that I am not damaging the HST tranny with bubbles. Is it normal to see bubbles on the dipstick? I overfilled the trans by about a 1/4" on the dipstick back about 400 hours ago and run it that little bit high. Oh and I have made an effort to run the engine at 2000 RPM when moving to see if the bubbles go away and they don't.

Not a lot of bubbles and the color, smell, is fine. Thoughts?

J_J · Apr 22, 2009

I believe that you probably have a small suction leak. Check the intake hose on yor pump. Sometimes when working the cylinders hard, you will draw a vacuum, and suck in some air, which will eventually get back to the reservoir.

kennyd · Apr 22, 2009

A few bubbles would be normal as the fluid coming back into the sump settles, actual "foaming" would look like it had soap in it.

Highbeam · Apr 22, 2009

So it might look like soap, there is a definite cutoff at the top of the liquid vs. a scumlike layer of suds but the dipstick will have several little pinhead sized bubbles. This is a hydrostatic tranny machine.

So what do I look for on the suction line? Nothing is leaking out that I can see. Do I run the engine and try to dribble oil on the joints looking for suction? Oh and which line is the suction line? I assume it is the big one that runs along the bottom with O-ring seals.

Will my small overfill cause foam?

TBDonnelly · Apr 22, 2009

Not sure if this would cause foam but, have you blown out the vent on the HST tranny lately?

Don

kennyd · Apr 22, 2009

The suction line is the big one, I don't believe an over fill would cause any problem like this at all...there is such a large margin for error because of all the cylinders that can be hooked to your tractor pulling fluid from and dumping fluid into the sump.

If your return line (suction line) and/or filter has dents like it's been beat up under there than it may be prudent to change the filter and put some fresh O-rings on you pipe...

BTW...I remember the thread that got you thinking about this, and I doubt your issue is anywhere near the problems he had...

J_J · Apr 22, 2009

Highbeam,

Is the fluid actually foamy or just a few bubbles? Is there just a top layer of foam?
Bubbles usually rise to the top, and the draw for the hydrostat is probably a couple inches above the bottom. Does your hydrostat draw fluid through a filter?

Highbeam · Apr 23, 2009

Several bubbles along the length of the dipstick, no actual foam but I can't say I've ever seen foamy hydro fluid to know. This is not the same type of foam that makes up the "head" of a glass of beer for example.

The hydrostat has a seperate filter that is unique to HST models of my tractor but I am not certain of how the fluid gets there. The sump is common to both the trans and the hydraulic system. All UTF.

No filter damage though I am coming up on 800 hours where I get to do an extensive filter and fluid change. The suction line runs lower than the sump so I fear that having to replace the seals along that line would require dumping the 7 gallons of oil.

So does anyone with a HST Kioti ever see bubbles on their dipsticks after working the machine? I would love to be able to dismiss this as normal but the cost of a failure is very high.

TBDonnelly · Apr 23, 2009

I've checked the HST dipstick several times recently since rebuilding the leaky curl cylinders on the FEL but did not note any bubbles on the dipstick. However, I have not had a long outing with the tractor recently to comment on bubbles on the dipstick.

Don

Highbeam · Apr 23, 2009

I can see that this is one of those cases where a picture is worth a thousand words.

Should I hear a sucking sound or see any fluid leaking with a suction leak? Would the power of the suction leak be based only on engine RPM since the pump is in theory always moving the same amount of fluid?

Thinking I can go around with an eye dropper type device to try and check connections. Is that a decent idea?