Hydraulic Oil - what do the numbers mean?

[dourobob]

My tractor manual calls for SAE 20 Hydraulic Oil in the power steering pump. I was in the local TSC store yesterday and the closest number they had was Castrol ISO 32 A.W Hydraulic Oil (no SAE numbers on the jug).

Can anyone tell me the difference between these SAE and ISO numbers?

Would ISO 32 work in an SAE 20 power steering pump without doing damage?

Are there better options?

Thanks
Bob

 

[Wingnut]

ISO and SAE are different ... ISO is the viscosity ... whereas SAE is the "grade.
For example, on the product data sheet I'm looking at right now, SAE 40 has a viscosity of 130 (this is for a specific diesel oil). I haven't found an equivalance chart ... but I'd say that 32 will be WAY too heavy fo rthe power steering. You'd want an AW 120 or 160.
Nut I'm very surpised to see the recommendation for SAE 20 hydraulic oil .... all of my analysis in the past month (I just happen to be reseraching lubricants) shows hydraulic oils using ISO viscosities.

pete

 

[jrlichina]

You have things backwards. Viscosity is the property of resistance to flow in a fluid so the higher the viscosity number the thicker/heavier the fluid. Also SAE stands for Society of Automotive Engineers and ISO stands for International Organization for Standardization. SAE is US based and the other an international body each have thier own definitions, classification, etc. for all kinds of things which I won't get into. Grade is used to simplify the selection of a oil of a given viscosity index. Using your example it should have been stated: An oil SAE 40 has a viscosity index of 130. A recommendation of SAE 20 is very typical in hydraulic applications. AW 120 or 160 should NOT be used due to it's high viscosity. These grades are used in applications like simple manual transmissions, gear driven transfer cases, front/rear drive axles, etc. In hydraulic applications the viscosity of the fluild is based on many factors like type of pump, open/closed center system, accumulators, cylinders, oil coolers/no oil coolers, etc. I hope this helps.

 

[dourobob]

Thank you gentlemen
While I feel I am becoming more knowledgeable I am not any closer to knowing what to put into the power steering reservoir on my tractor. I did make a slight error in my original spec as it is actually calling for SAE 10 W Hydraulic (Not 20 - I was reading the wrong line). From what has been said this would be even lighter.

A local tractor dealer offered to sell me a multi grade mineral oil that ranges from 7 to 15?

I am very reluctant to put in anything that could gum up the pump and woudl be really happy if I could find an exact equivalent to SAE 10W Hydraulic Oil.

Any suggestions.

Bob

 

[DFB]

An ISO 32 has the viscosity equivalent of an SAE 10w oil.

An ISO 68 rating would equal an SAE 20w oil requirement.

John Deere's LOW VISCOSITY HY-GARD (JD20D) has a viscosity rating of 32cST@ 40C. That's what I use.

Regular HY-GARD (JD20C) is 58 cST@ 40C.

http://www.hascooil.com/faq/viscosity_table_faq.html

DFB

 

[dourobob]

Excellent.

Thanks for the info and the reference table.

Very helpful.

Bob

 

[Soundguy]

At least my NH takes the same oil in the power steering as in the rear end / hyd resevoir , and the front final drive.

Not so much oil types to keep track of...

Soundguy

 

[markie61]

</font><font color="blue" class="small">( Not so much oil types to keep track of... )</font>

A big AMEN to that, brother!!!

Mark

 

[Wingnut]

THWACK ... (sound of hand hitting forehead) ...
you're right, of course .... fingers engaged before head fully involved.
All the applications I "support" are for very high viscosity oils ... I'm used to talking in terms of 120 being the low end and 2200 being on the high end.
Apologies for the confusion and thanks to jrlichina for being quick to correct me.
I've never seen SAE soecs used for a hydraulic application ???
All the ratings that I'm familiar with from locomotives through walking draglines use either ISO or just the viscosity index (which usually amounts to exactly the same thing).

pete

 

[dourobob]

Thanks to all of you. I talked to a local "Oil Expert" who says when he goes to seminars put on by the industry it isn't just an excuse to drink beer - he actually attends the presentations. He told me (and used the same chart referenced by DFB) that ISO32 and 10W are the same. Apparently ISO ratings came into use in North America about 15 years ago and, as my tractor manual calling for SAE 10W is about 20 years old, well ....

So, now I am back on the repair tasks with my power steering connections on the tractor.

Bob