Hydraulic fluid foaming?

[Highbeam]

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]

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]

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]

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]

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

Don

 

[kennyd]

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]

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]

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]

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]

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?

 

[J_J]

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?

No, you won't hear a sucking sound unless you have a severe leak. and then you will really see a lot of bubbles, and foam.

If you have an 8 GPM pump,at 3000 psi, at max RPM, that only means that at the highest RPM , and you have enough resistance to the pressure, then you will produce a pressure of 3000 psi. At low RPM, you might be only 2 GPM, and if you have some resistance like a cylinder lifting a half load, then you might see 1500 psi. A hydraulic gage is very handy to have and use.

 

[IslandTractor]

I don't know if this is relevant as you have double checked your HST fluid levels but I had a lot of foaming one day with my CK20 when I inadvertently overfilled the HST oil reservoir. In my case it was due to checking the fluid level before running the motor then adding fluid when it appeared to be low. It doesn't sound like that is your issue though. Nevertheless, it does seem that one cause of foaming (my fluid was a light brown is was so foamed after mowing) is too much HST oil. I never saw foam again after realizing my error and draining the excess oil.

 

[Highbeam]

Hi IT, how overfull was it to cause the foam? I am a healthy 1/4" above the full mark when the 3ph is at half and the loader is on the ground.

 

[J_J]

Are you checking your fluid cold or hot. It will expand and show more on the dipstick when hot?

 

[Highbeam]

Checking when warm, we haven't had enough grass grow yet to really heat it up.

 

[IslandTractor]

Hi IT, how overfull was it to cause the foam? I am a healthy 1/4" above the full mark when the 3ph is at half and the loader is on the ground.

I had checked the fluid before starting the engine that day and noted the level was very low (below minimum). Loader would have been on the ground and 3PT would also have been down with a mower on it. I therefore filled it to the max normal level and then just started and used the tractor without rechecking. I imagine that the original level was probably within the normal range really and that it was just the vacuum lock or whatever phenomenon is responsible for giving low readings before starting the engine. I therefore think I added about a quart or maybe a bit more than needed so I'd guess there was an extra quart above max.

I did not notice anything wrong until I stopped mowing a couple of hours later and saw a small amount of HST oil bubbling out of the dipstick tube. When I checked the level I immediately saw the foamy light brown fluid full up the dipstick tube. I muttered and scratched my head but did not check again until the next morning when the foam was gone and I saw that the reservoir was way overfull. After draining out about a quart all was normal afterwards.

 

[TBDonnelly]

I had checked the fluid before starting the engine that day and noted the level was very low (below minimum). Loader would have been on the ground and 3PT would also have been down with a mower on it. I therefore filled it to the max normal level and then just started and used the tractor without rechecking. I imagine that the original level was probably within the normal range really and that it was just the vacuum lock or whatever phenomenon is responsible for giving low readings before starting the engine. I therefore think I added about a quart or maybe a bit more than needed so I'd guess there was an extra quart above max.

I did not notice anything wrong until I stopped mowing a couple of hours later and saw a small amount of HST oil bubbling out of the dipstick tube. When I checked the level I immediately saw the foamy light brown fluid full up the dipstick tube. I muttered and scratched my head but did not check again until the next morning when the foam was gone and I saw that the reservoir was way overfull. After draining out about a quart all was normal afterwards.

You have me wondering if your HST vent may have been plugged...

Don

 

[Highbeam]

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

Don

No, never, I'll get right on that. The red rubber has faded into pink and there is an oily dark spot below the little outlet from the vapor I assumed. Easy to clear and check.

I think I will plan on removing some fluid soon to get the fluid to within the dipstick range. As I recall, the final drives had only a small amount of UTF in them so it should be easy to control the release.

 

[TBDonnelly]

No, never, I'll get right on that. The red rubber has faded into pink and there is an oily dark spot below the little outlet from the vapor I assumed. Easy to clear and check.

In case anyone is wondering where the vent on a CK30 HST is, here's a couple pictures.

Don

 

[IslandTractor]

You have me wondering if your HST vent may have been plugged...

Don

If a clogged vent would cause there to be "hydro fluid lock" as the tranny cooled down the night before I checked the level cold then perhaps that was a factor. That might have mislead me into thinking the level was low. I would have removed the cap/vent in order to put more fluid in and perhaps that cleared any clog. I did not specifically look for a clog or notice one.