20W-50 for a hydraulic pump in a hydrostatic trans

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Posted in another section about a VST 205-024c Peerless trans in a murray mower but want some opinions on the best fluid.
There are two chambers (one is easy, takes 80W90). The other is controversial...

The choices are a mystery peerless oil vs 20W50(which many say works exceptionally).
20W50 comes in Motorcycle flavor or race oil (which has lots of zinc).

The mystery oil has to be delivered and is expensive, and I'm leaning to a synth 20W50. Any opinions on this? Probably anything would be better than what came out of it!
 
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Hydraulic oil usually doesn't have moly or zddp in it because those additives will form sludge in a gear box. They also have protection for yellow metals.

You can buy 20 weight hydraulic oil cheap at tractor supply. 30 weight too. There's also syncromesh.
 
What's your typical max/high side operating temperatures of the two chambers i.e 80W90 and 20W50(recommended by OEM?) as well as lowest/highest ambient temperatures?
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This unit is essentially a throw away unit, but it will be running in temps say 32-95. No winter.

Maybe in light of this the OEM fluid is best to get?


I see people using the 20w50 motorcycle oil for years, and some manufactures suggest exactly that fluid.
 
Originally Posted By: Oldmoparguy1
Isn't that the unit that many are using M1 15W-50?

That or 20W50. Some guy updates that his is running great for years.

Don't motorcycles have a similar wet clutch system?
 
My Toro Z master commercial calls for Mobil 1 15-50. It's 12 yrs old. I change it every other year. It has separate pump/motor and is commercial grade.
 
I run Castrol or Mobil 5W50 syn and have for years on my Tuff Torq K51. I have over 1000 hours of trouble free use. I have used 20W50 conventional with no problems on various hydrostatic transmissions.
 
5W may be good for winter, this is a summer tractor.

Guess M1 or synth 15W-50 or 20W50 will be fine. The mystery fluid is supposedly synth, and this unit has a pulley fan and runs hot.

Whatever is cheaper at the Wally.
 
No, at that temperature (pretty much anything above 50 degrees) the viscosity of the three oils is going to be very similar. Nothing is really known about the 20W-50 but between the Mobil 1 oils it is very close.
 
Originally Posted By: ford46guy
Originally Posted By: Oldmoparguy1
Isn't that the unit that many are using M1 15W-50?
That or 20W50. Some guy updates that his is running great for years.


You already had the proper selection.
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Went with M1 20W50 VTwin, was 2 bucks off a qt at the Zone over memorial day(Motorcycle season?). I also ran it by a volume small engine shop when I bought my bolts, they said they offer it as an $30 option for extreme use. Otherwise they use conventional store brand 20W50. He said in that unit it is likely lifetime.

Mower is about 20% faster with the new oil. I have a distance that I benchmarked. Case was hot enough to be hard to touch after mowing for an hour, now it is luke warm.

Took 1 qt + about 12 oz. Rest goes in my lube can. Nice thick oil.

Other side got 80W90 VV durablend synth (had some left over, took about 20 oz).
 
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