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  1. #1
    Platinum Member
    Join Date
    Mar 2010

    Default BX HST foam / air entrainment in oil -- HELP!

    I have a BX1860 (ca. 2010) with ~190 hours on it. For the most part I use it for mowing (MMM) and some FEL work (mulch and topsoil).

    A couple of weeks ago, in prep for this mowing season, I changed all the filters and such -- including the HST filter. This is the second time I have swapped the HST filter, the first at 50hrs. After changing the filters I added about a pint of OEM kubota SUDT to get the HST level back at the high mark. Subsequently I cut the grass for the first time, and then moved some mulch, with both tasks uneventful. The MMM PTO and FEL had no power issues nor was forward or reverse movement problematic in any way whatsoever.

    But more recently I have noticed some driveline vibration. This only happens when the HST pedal is pressed in around the midpoint of slow-to-fast, and it happens in both in forward and reverse. I have been working through diagnosing exactly what circumstances produce the vibration. It happens in both low and high range. It happens whether the MMM PTO is spun up or not. It happens whether the FEL is mounted or not.

    The other thing I noticed after doing some FEL work moving a few yards of topoil was that the QD fittings were quite warm. I don't know if I had ever noticed this before; it just so happened that since I wanted to mow the next night I took the FEL off right away so I was ready to cut. In other words I went from moving topsoil to taking the FEL off with just two minutes or so between dropping the last FEL bucketful to decoupling the QD's.

    Last evening after I got home from work I rechecked the HST fluid level when the BX was cold. To my surprise it was slightly high, perhaps up 1/4" from the high mark on the yellow dipstick. Using some clear poly tubing, I siphoned about a half pint back out. The level at that point in the transmission sump was right at the top line on the dipstick. The HST fluid is clean and clear -- there is no sign of water or other contamination. I started the BX and as I let it warm up I went forward and backward about 15 feet without issue. I engaged the MMM PTO and then brought the throttle up to 3K RPM without issue. This is the standard way I would prep for starting to mow (the area I cut is about 1 acre).

    Rather than starting mowing, I decided to shut the BX back down and recheck the HST fluid level. In doing so I noticed that the oil was quite foamed down in the dipstick hole. There was about 1/2" of foam on top of the oil. This bothered me a bit so I cancelled the plan to mow and decided to do some reading. It's not clear to me from looking at posts here and on other sites whether foaming in the HST reservoir is normal or not. I don't think I have ever checked the HST oil after the tractor had been run first so I have no idea whether or nor this degree (or any amount) of foaming is normal.

    Based on what I have read here and on other sites there are apparently a couple of usual suspects of air entrainment in the oil: leaking HST filter gasket, leaking hose, or "other".

    SO: considering what you guys have read above, do you have any thoughts? Am I just paranoid? Did 4 months w/o tractor operation make me forget it's a machine that vibrates a bit? Is foam in the HST reservoir normal? Should I re-replace the HST filter? Is there some obvious "check hose X because it rubs"?

    Any ideas?


  2. #2
    Super Member radioman's Avatar
    Join Date
    May 2008
    Ontario, NY
    Kubota BX24

    Default Re: BX HST foam / air entrainment in oil -- HELP!

    mine is a bit foamylike when checking immediately after shutdown. Id wait at least 15 mins or so before checking.

  3. #3
    Super Member dodge man's Avatar
    Join Date
    Oct 2008
    West central Illinois
    Kubota BX2350

    Default Re: BX HST foam / air entrainment in oil -- HELP!

    I hate to say it sounds normal, because without being there its tough to say, but it sounds normal to me. Mine will be a little foamy after running it, but not so bad its trying to come out the dipstick hole. Also, the hydraulic fluid will get pretty warm, so the quick connects for your end loader will get pretty warm.

  4. #4
    Elite Member dex3361's Avatar
    Join Date
    Aug 2008
    N. of Charleston WV
    Kubota L4400-1 HST,FEL, 3x3 remotes, TNT. BX1500 54 mmm

    Default Re: BX HST foam / air entrainment in oil -- HELP!

    If your tractor is in releif or if there is moisture in the hydro oil it can cause an abnormal amount of foaming. If you have a suction side leak allowing air into the hydraulic system it can cause foaming. If your suctin screen is plugging off it can cause the hydro to act funny and foaming. Did you clean the suction screen on the return line?

    1Timothy Chapter 2:
    3 For this is good and acceptable in the sight of God our Saviour;
    4 Who will have all men to be saved, and to come unto the knowledge of the truth.
    5 For there is one God, and one mediator between God and men, the man Christ Jesus.
    From: The HOLY BIBLE

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