Yanmar Hydro. Fluid

[neilw]

I'm from the green side of the Yanmar world or some would say the dark side.

I'm approaching my first hydro oil change and have been researching hydro oils. Of course JD recommends a low viscosity version of their own hydro fluid ( cSt viscosity at 100C 7.0 min.) for my model the 790. No one else makes a hydro. oil that has that low a viscosity at 100C.

What does the manufacture recommend?

Before you answer I suspect that Yanmar recommends a universal hydro oil that everyone else uses and JD uses the lower viscosity fluid to increase the PTO hp output. Sort of like the big three auto makers use 5w-30 and now maybe 5w-20 to meet their CAFE target.

For reference the 790 is a 30hp sliding gear 4 speed 2 range transmissioned machine with 26hp on the PTO.

 

[JeffRey30747]

I use a generic fluid that meets the JD 303 spec in my 186D. This spec should have been current at the time that most Yanmars were manufactured (regardless of whether they wore a red or green/yellow paint scheme).

 

[roger_scotty]

If I can paraphrase your question, it sounds to me that you are asking: "Why does JD all of a sudden specify an oddball viscosity in the trans-hydraulic fluid for a tractor built from parts that already have a good performance history with another oil spec?

Of course we don't know, but that won't stop us from having some fun with it. I'm going to take the side of doubting that the PTO HP is the reason. JD has been fairly honest on the HP game, and they spec. the 790 at 30 hp engine and 25 PTO...values which we know are normal with this engine/transmission package because it has been around for decades and well proven - Hmmm...I like your suspicious logic though ....maybe it has to do with fluid losses in that oversize dual open center hydraulic pump....If I were to look to cutting power losses I'd look first at that.

Another - and very likely - candidate is simply Yanmar's poor track record of converting between metric and US measurement systems. As you know, viscosity measurement and conversion is particularly troublesome. It wouldn't surprise me to learn that Yanmar got the conversion wrong and JD copied the erroneous values without questioning them.

 

[Soundguy]

Independent ( powered ) powersteering?

Soundguy


<font color=green>....maybe it has to do with fluid losses in that oversize dual open center hydraulic pump...

 

[roger_scotty]

Yep, the 790 has one of those 2 into 1 hydraulic pumps where one input shaft basically turns two separate hydraulic pumps that live in the same housing. One part for 3pt and accessories and the other for power steering. The good thing about that sort of design is that the power steering fluid flow is fed by its own pump, so there is no need for a flow divider - which is a tricky part to build and adjust. The downside to the "dual pump solution" is that power steering tends to want large flows at low engine RPM. So if you do the simple thing and design the steering pump oversize enough to steer at low RPM, it wastes a lot of power at higher RPM where it is squeezing far more oil than the steering will ever use.

 

[Soundguy]

It would also appear ( open design ) that a catastrophic failure of either system would also cripple the other system. In a 1 pump system, the same situation occours.. loss of hydro+loss of PS, etc.. but this way gives you the same 'benefits' at more cost, and w/ more moving parts to wear out... I've had experience with a similar situation.

The firm I work with has a commercial highway milling machine that had a cummins 290 on it. The design had a pto on one side of the tranny housing that operated a hydro pump, which was then coupled to a dc generator( pulley on back of the generator to further extend the power via v-belt to a cooling fan drawing air through the oil cooler... )... bearings go out on the generator, hydro goes out.... hydro shaft breaks.. no dc power... no aux. cooling...best yet, the coupling design was similar to a differential setup, but with a hard plastic center piece. At first glance, it looks like some kind of breakaway device, allowing the plastic to break, and drop the generator out of the system... but it wasnt... the top-bottom pieces could contact the side-side pieces if the plastic gave way.. whole system runs unballanced for a minute, then the pump shaft breaks ( actually happened ).

After fighting with the system with a couple of years, we traded the engine out for a 300 and different pto and add on setup. Total nightmare.. I spent way too much time trying things to make that machine work...

Soundguy

 

[neilw]

Wow. What an education. Thanks

 

[kayssupply]

I am still waiting for someone to tell us the difference between TF300 and TF500. They appear as spec on different grey Yanmars. The FX175 I just got has TF500 in the front end and the transmission.