What oil offers best protection for Hydrostat pumps/motors?

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Greetings,

Some of the hydrostat systems I service call for a 20w-50 motor oil instead of a true hydraulic oil or even UTF. My question, is what attributes should one look for in a 20w-50 for best protection? Do differences in friction modifier levels or ZDDP levels matter more?

The two subgroup options I can think of are simply motor oil, and motorcycle oil in the specified grade.

One high end option I am considering is Redline 20w-50 which is polyol ester base stock based with and SN rated.
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Another option below is Redline motorcycle 20w-50 that apparently is PAO and Ester base stocks and 2200 ppm of ZDDP for antiwear and rated SJ with JASO MA/MA2.
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Just "20w-50 engine oil". Hence dissecting academically if there is any benefit between motorcycle older SJ oil specs and newer SN oil specs when it comes to wear inside the system.
 
No need to over think this.
If they required a motorcycle type oil, i.e. JASO MA, MB etc, I would think they would state it.

Typically in industry, we look for the most reasonably priced product that meets the OEM specifications.

There is no justification for using a premium product unless prior performance data has indicated that the OEM spec is substandard.

Is your current MTBF too short?
Does used oil analysis of your current lubricant indicate a problem?
How would you justify the increase in lubricant cost to a reliability engineer or to the larger engineering team.?
 
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Update: The manual actually does specify SL. "Typically, an engine oil with a minimum ratingof 9 .0 cSt (55 SUS) at 230°F (110° C) and an APIclassification of SL is recommended. A 20W-50engine oil has been selected for use by the factory and is recommended for normal operatingtemperatures . Biodegradable oils are not ap-proved for this unit as they degrade too quickly while in service ."

1. This admittedly may be overthinking, but like I said since it requires 20w-50 I am simply looking for an academic discussion about what should provide the best protection. I am sure the choice to use motor oil instead of a actual hydraulic fluid for example, was a choice based on what oils would be easy for the average consumer to find. This choice may or may not be a compromise?

2. Also for consideration: To keep them in warranty I am interested in using the best possible oil (that still meets 20w-50 specified in the manual).

3. To add to the variables, some of the units involve a planetary gear reduction similar to the illustration below. Is a SN oil sufficient for this type of gear reduction in an oil bath or would a SJ oil offer benefit due to ZDDP levels or is SN good, or possibly better?

Thanks!
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1. ........I am sure the choice to use motor oil instead of a actual hydraulic fluid for example, was a choice based on what oils would be easy for the average consumer to find. This choice may or may not be a compremise?
Not necessarily. The motor oil spec would likely be a result of the working conditions if the machine. Industry typically assumes you have access to the spec'd lubricant. That is what industrial lubricant suppliers exist for.

2. Also for consideration: To keep them in warranty I am interested in using the best possible oil (that still meets 20w-50 specified in the manual).
To keep them in warranty, you use a reasonably economical lubricant that meets the OEM spec. You don't use 'the best possible oil' (whatever that may be) unless you have data to justify the cost differential.

3. To add to the variables, some of the units involve a planetary gear reduction similar to the illustration below. Is a SN oil sufficient for this type of gear reduction in an oil bath or would a SJ oil offer benefit due to ZDDP levels?
Unless the OEM states otherwise, industry assumes that you use the latest service category for the viscosity grade specified. That is why new service categories are backward compatible. If an SH, SJ, etc oil was required, the OEM would have stated it.

With all that in mind, there are certainly exceptions and special circumstances that would be counter to what I have stated above. Those circumstances usually come with a raft of machinery failures, extended downtimes and reduced throughput. From what the OP has stated, these types of circumstances are not part of the situation.

Good luck!!!
 
Not necessarily. The motor oil spec would likely be a result of the working conditions if the machine. Industry typically assumes you have access to the spec'd lubricant. That is what industrial lubricant suppliers exist for.


To keep them in warranty, you use a reasonably economical lubricant that meets the OEM spec. You don't use 'the best possible oil' (whatever that may be) unless you have data to justify the cost differential.


Unless the OEM states otherwise, industry assumes that you use the latest service category for the viscosity grade specified. That is why new service categories are backward compatible. If an SH, SJ, etc oil was required, the OEM would have stated it.

With all that in mind, there are certainly exceptions and special circumstances that would be counter to what I have stated above. Those circumstances usually come with a raft of machinery failures, extended downtimes and reduced throughput. From what the OP has stated, these types of circumstances are not part of the situation.

Good luck!!!
I must have been updating while you were posting :)

Update: The manual actually does specify SL. "Typically, an engine oil with a minimum ratingof 9 .0 cSt (55 SUS) at 230°F (110° C) and an APIclassification of SL is recommended. A 20W-50engine oil has been selected for use by the factory and is recommended for normal operatingtemperatures . Biodegradable oils are not approved for this unit as they degrade too quickly while in service ."

Does that change anything for you? Thanks for you input to the discussion!
 
My real zero turn, A Grasshopper 430D just calls for a hydro fluid change every 1,000 hrs. Their branded fluid is $20~25/qt and it takes 4.71 quarts. I've not been able to find out anything about this fluids properties other than it contains mineral oil and zinc alkyldithoiophosphate. But for a 1,000 service interval, I guess that's better than most.



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Clean oil that meets the specs offers the best protection.
Based on the manual stating "Typically, an engine oil with a minimum ratingof 9 .0 cSt (55 SUS) at 230°F (110° C) and an APIclassification of SL is recommended. A 20W-50engine oil has been selected for use by the factory and is recommended for normal operatingtemperatures . Biodegradable oils are not approved for this unit as they degrade too quickly while in service ." would you prefer an SJ rated 20w-50 or a SN 20w-50?
 
My real zero turn, A Grasshopper 430D just calls for a hydro fluid change every 1,000 hrs. Their branded fluid is $20~25/qt and it takes 4.71 quarts. I've not been able to find out anything about this fluids properties other than it contains mineral oil and zinc alkyldithoiophosphate. But for a 1,000 service interval, I guess that's better than most.



61SFbdqrV4L._SL1200_.jpg

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Interesting, I had no idea Grasshopper had their own fluid. I imagine that 1000 hour interval is paired with a decent oil cooler and good filtration.
 
I must have been updating while you were posting :)

Update: The manual actually does specify SL. "Typically, an engine oil with a minimum ratingof 9 .0 cSt (55 SUS) at 230°F (110° C) and an APIclassification of SL is recommended. A 20W-50engine oil has been selected for use by the factory and is recommended for normal operatingtemperatures . Biodegradable oils are not approved for this unit as they degrade too quickly while in service ."

Does that change anything for you? Thanks for you input to the discussion!
Ok so now you need to determine if the SL spec is specific to the application or if it was just the current spec at the time of manufacture. A quick call to the OEM tech service line should clear it up.
From there, you're golden.
 
Amsoil 20w50 Synthetic Hydrostatic Transmission Fluid (AHF) may be a option. Using it in my SCAG and like the feel over what OEM was filled with.
 
Based on the manual stating "Typically, an engine oil with a minimum ratingof 9 .0 cSt (55 SUS) at 230°F (110° C) and an APIclassification of SL is recommended. A 20W-50engine oil has been selected for use by the factory and is recommended for normal operating temperatures . Biodegradable oils are not approved for this unit as they degrade too quickly while in service ." would you prefer an SJ rated 20w-50 or a SN 20w-50?
I couldn't say which oil would be Better. I would if my choice of between the two, posted above the Redline car oil ,still changing as per recommended
 
Interesting, I had no idea Grasshopper had their own fluid. I imagine that 1000 hour interval is paired with a decent oil cooler and good filtration.
Yes, In addition to the pump fans, I do believe there is finned heat sink in the system and of course a spin on fluid filter. I only have about 500 hours on the unit, but after this mowing season I am going to replace the hydro fluid. I was thinking about using a less expensive fluid, but as I purchased this around 2012 and this would be the first fluid change the cost per year would be negligible even if I went with the Grasshopper brand.
 
Looking up by my mower Cub Cadet recommends to only use Cub Cadet Hydrostatic Transmission Oil.

Searching by the model of the hydrostatic unit Hydro Gear recommends either 10w40, 15w40 or 20w50 motor oil. I filled mine with Super Tech 15w40 about 6 years ago and have had no issues. It might be worth looking into the recommendations specifically for the hydrostat unit.
 
Well.. my take is that given the long service interval, cost is not really an issue. At lest for me, I do not mind dropping 10-20$ per quart, esp if that buys me some extra longevity and improved reliability . Trying to save some money on the lubricant is simply not a consideration for me.
The per year cost works out to something manageable in any case.

The hydros are a high temp, high shear environment. There is no combustion, so acid neutralizer (TBA) content is probably not relevant.
No cat converter, so high anti-wear additive levels are OK. My sense is that high viscosity index is probably not important, since, the
typical use is not cold temp. The very high viscosity indexes are usually achieved by friction modifier additives, which
tend to shear down to some degree. So I would stick w thew 20w50 recommendation, unless there is a good
reason for a lower winter viscosity.

I am thinking: a high quality true synthetic 20w50 , with maxed out anti-wear additives. So on that count the redline motorcycle oil sounds
pretty good to me. The ester content in the base stock should help eliminating carrier ( usually dyno) oils for the additives, as it is an excellent solvent for those. Expensive, but at least you know what you are getting, instead of just some marketing claims such as "superior performance" .

I don't much care of the "Cant tell you what base stock we are using, it is a trade secret".
Seriously? For my hard earned money, I require that a manufacturer goes on record and discloses what base stock(s)
are used in their product. No disclosure, no buy. Esp. if I see from the MSDS that they are using a significant amount of
the cheaper group 3-s yet charging top $$$. So in general I mistrust the highly hyped/marketed boutique oils such as Royal Purple
and Amsoil. I could be wrong and those may be actually fine products, but simply, some key info is withheld.

A low "W" oil, (to me) implies 2 things: Better cold starts when it is very cold, and a higher viscosity index. I do not believe either is beneficial in the hydro/zt use case. Because of some amount of shear down, esp. over the expected many year service interval, I would like to have some extra margin on the 120 celsius cSt number, so after a few years it still meets the minimum recommended. All this so far implies a high quality, true synthetic oil. The 20w50 redline motorcycle oil does actually look good to me. I am on the fence on whether the oil should be detergent. Since there are no ashes or other combustion blow-by, I am thinking "detergent" is not relevant. You cant go too wrong with a M1 20W50 either,
where the base stocks are PAO+GTL these days.

I recall reading on this forum, that the reason for the motor oil preference is the high heat operating environment. Something about gear lubricant being too thick for this. For example I read the a sometingW60 oil is worse for a very hot application than a W50.

I dont claim to be a lubrication expert, just tabulating the data from what I am reading.
 
I did a bit more research, and it turns out that TBN may be relevant relevant. Gravely has their own branded 15w50 synthetic
"hydro oil", which turns out to be a Mobil-1 15w50 extra (some older product manuals actually state this) . When Gravely talks about this lubricant, they mention "high TBN" as if it was a good thing. The m-1 15w50 has 1200 ppm zddp, it looks like a pretty solid bet.

Motorcycle oils sometimes contain friction modifiers to make them work better with wet clutches, not sure if that is an issue for the hydro. I think the point is to increase the friction to prevent the clutch from slipping. I have always wanted to try redline, I will try it as my engine oil on ther Kawi Fr691 I have. Slightly unrelated, Kawasaki has a "KTECH" synthetic motor oil, it looks like that is mostly group 3, based on the msds.
 
Your way over thinking this your working on Hydro-Gear transaxles in a garden tractor cub cadet, craftsman, husky, etc.. etc..? if manual calls for a SL 20w50 then use it nothing special is required, or what allot of guys on tractor forums use is M1 15w50 witch has lots of Zinc and works just fine, my HGG730 in my cc states the same thing in the Hydro-Gear service manual, I use 15w50
 
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