Path of hydraulic fluid to engine crank case.

[Raised on a Deere]

My Yanmar LX490 with about 1300 hours has suddenly started filling the crankcase with hydraulic fluid. This same engine is on some John Deere models. Crank case gains, probably a pint to a quart in about 3 hours of running. Problem initially showed up with engine blowing blue smoke at start up and taking several minutes before it would respond to throttle. Initially thought it was a fuel problem. In the head scratching phase I pulled the dip stick and it was way high on stick. No smell of diesel fuel but consistency was very close to the feel of hydraulic oil. I drained about 3 quarts out and ran the tractor for about 3 hours putt putting around doing some dirt moving and moving rocks, low rpm stuff. Now level is definitely up. Hard to tell from hydraulic dip stick if any missing but seems to be down somewhat.

The only path I can think of for the hydraulic oil into crankcase is via the two hydraulic pumps(power steering and hydraulics) on left side near front of engine driven off camshaft I believe. Each pump is driven by the same gear I believe and I have a diagram showing a shaft seal on each pump. I have ordered two seals but have not yet torn into things. Doesn't appear to be too big a job to replace the seals but I am wondering what to expect to see when I remove the pumps. No way to see the seal under pressure and the seal end is bathed in crankcase oil. For now I am ruling out worn pumps because of low hours and hydraulics are performing well under heavy loads.

I have gathered from what little information I can find that bad seal could cause this problem but also that worn pump can let too much fluid flow back to the seals and thus over pressuring them.

1: how would you diagnose worn pump?
2: how do you observe that the seal was actually leaking if it is not torn or fragmented in any way
3: how could I determine which pump is leaking. They both use common sump and connect to engine by same gear.
4. Tractor has hydraulic reverser clutch so I am wondering if there is a path there for hydraulic fluid into crankcase. Inconceivable to me but I just don't know. I have worked on just about everything there is except hydraulics. I have been one of the lucky ones whose hydraulics always worked.

I do remember the tractors on the farm I grew up on had front mounted pumps driven off the end of the crankshaft. You could see the seal leak and my dad replaced a pump on a 2020 John Deere.

Any experiences like this from any of you would be appreciated. I just need a little more light on the subject.

 

[Roadworthy]

I have no John Deere or Yanmar experience. My Mitsubishi tractor only had one hydraulic pump. The pump seal was a path from the hydraulic system to the crankcase. I don't know if you CAN tell by examination which seal in which pump has failed. If you can do it easily you may just wish to replace both. They are a gear type pump, that is two meshing gears make the pressure. It takes a LOT of use before they wear out. My 1942 D4 Cat was still running the original gear pump when I sold it last year.

 

[ptsg]

The only way I can think of is the shaft seal on one of the pumps going bad.

Make sure the vent for the transmission/hydraulic oil is not clogged as it can create backpressure on the inlet side of the pump and blow the seal out.

The shaft seal on gear pumps is a low pressure seal.

 

[TMGT]

Most likely the pumps internal seals are starting to fail, this will cause the shaft seal of the pump to start leaking into the crankcase. If you just replace the pumps shaft seal you will most likely be pulling the pumps back off.

I recently had this same problem on my forklift, actually it had the problem when I bought it (was able to get it at a good price). The seal kit was about $60 for my pump and they are pretty easy to replace.

If it's not the seals then your pump might be getting worn out.

 

[Jim Nelson]

I had a B7200 Kubota that started dumping hydraulic oil into the crankcase and thought it had to be the shaft seal after doing some research. I replaced the seal which was easy on that tractor and it continued to leak so I just replaced the pump. At that time the price wasn't that bad and I had work to do so didn't mind. The new pump fixed the problem. The hardest part of the whole experience was 2 oil and filter changes.

 

[Raised on a Deere]

Thanks, hearing from those who have been through this helps. Pump is almost $500 each and I would have just bought a new one but there are two as I mentioned, Power steering and hydraulic. So which one is the next thing.

I will just do shaft seals and see what happens. Somehow I don't see a shaft seal just suddenly going out, but hope so. Perhaps something becomes obvious once I get it apart. Parts should be here in 3 more days. Now I am trying to decide whether to try to work on this thing with loader on or off. I have never had it off but supposedly it is a pretty quick thing to do.

 

[TMGT]

I would at least pull the pump appart while you have it off. The shaft seals are a low pressure seal, maybe a couple hundred psi max, any failure of the seals that separate the gear section from the case will cause the shaft seal to fail.

Its almost a guarantee that the pump that actually attaches to the engine is the culprit (typically this is the implement pump) if the rear pump fails it will usually result in an external leak or a performance problem.

Here's a picture of a shaft seal that failed due to the high pressure gear section seal failing. Had i just replaced the seal, it would have blown out again as soon as I activated anything in the hydrulic circuit.

 

[Kernopelli]

I had a similar issue with a Mitsubishi K3F engine. The pump seal blew out and allowed enough hydraulic fluid to flood the top end and it actually caused an engine runaway scenario. My son was using the tractor when it happened and had the presence of mind to choke the air intake before anything catastrophic happened.

 

[Raised on a Deere]

I would at least pull the pump appart while you have it off. The shaft seals are a low pressure seal, maybe a couple hundred psi max, any failure of the seals that separate the gear section from the case will cause the shaft seal to fail.

Its almost a guarantee that the pump that actually attaches to the engine is the culprit (typically this is the implement pump) if the rear pump fails it will usually result in an external leak or a performance problem.

Here's a picture of a shaft seal that failed due to the high pressure gear section seal failing. Had i just replaced the seal, it would have blown out again as soon as I activated anything in the hydrulic circuit.View attachment 670943

Thanks for for your suggestions and the picture. Looking at that pic as you say, that is sure appears to be caused by excess pressure from some cause. If I see anything like that I will just go ahead and order a pump probably. The diagram for my pump does not clearly show any other circular seals. There is one part that looks like some kind of odd shaped part that is called a seal. I am tearing down today, shaft seals due at noon.

 

[TMGT]

Most likely that odd shaped seal is what isolates the gear section from the case. The pump in that picture had that seal fail, it was made out of a urethane material and had hardened and started to disintegrate.

These are examples of some of the different internal seals. (The pump I showed used the seals on the far left for example).