More Kubota Confusion

[Jay4200]

OK, I did search but I have not found the answer.
Kubota M9540 - manual says for the front axle case and the front differential that you can use either UDT Hydraulic fluid OR SAE 80-90 gear oil.

There is a big difference in these two types of oil. Dealer says they put in UDT Hydraulic fluid whenever they do fluid changes.
I am not questioning the dealer, I just wonder how the thinner hydraulic fluid can be OK for the axle case and differential.

It's not really all that different. UDT is equivalent to about a 20w (SUDT is ~10w), and 80-90 gear oil is roughly 30wt, so they are pretty close. Gears don't care.

I'm running 85w-140 in mine. It's like molasses in January. Not to say it's the best thing to put in there, but it helps keep my bezel seal leak under control

JayC

 

[jdjdjd]

I just read on Messick's site that they recommend replacing the factory UDT with SAE 80W-90 Gear Lube.

Their quote: "Summary:
Often times front axle housings are filled with the same fluid that the transmission is. This is perfectly acceptable as a good quality fluid is used from the factory. When changing this oil consider upgrading to an 80W-90 weight oil. This is suited best for use in heavy duty gear boxes."

 

[clemsonfor]

It's not really all that different. UDT is equivalent to about a 20w (SUDT is ~10w), and 80-90 gear oil is roughly 30wt, so they are pretty close. Gears don't care.

I'm running 85w-140 in mine. It's like molasses in January. Not to say it's the best thing to put in there, but it helps keep my bezel seal leak under control

JayC

I dont claim to be an oil expert, but know a good bit and a ton more than any guy off the street, but how is 80W-90 the same thickness as 30W. The gear oil acts like 80wt cold and 90 wt warm and 30wt is 30wt?

 

[284 International]

Clemson, it has to do with how the lubricants are rated by the SAE for their purpose (gear oil or motor oil). Here is a chart showing the viscosity differences. At "cold" temperatures, like room temperature, there may be a lot of difference in viscosity between gear oil and motor oil of, say, 80w-90 and 30w. However, the oils are rated at 100C, or 212 Fahrenheit. If you warm the containers up in boiling water, the two lubricants will be the same viscosity. :thumbsup:

 

[sw03]

I run Amsoil grear fluid in my front diff since UDT does NOt have the same properties as a gear fluid...Hence, why they make it.

 

[clemsonfor]

Clemson, it has to do with how the lubricants are rated by the SAE for their purpose (gear oil or motor oil). Here is a chart showing the viscosity differences. At "cold" temperatures, like room temperature, there may be a lot of difference in viscosity between gear oil and motor oil of, say, 80w-90 and 30w. However, the oils are rated at 100C, or 212 Fahrenheit. If you warm the containers up in boiling water, the two lubricants will be the same viscosity. :thumbsup:

i see, isint this kind of confusing? i guess this is what the GL and the crankcare rating are for to tell you.

 

[Jay4200]

i see, isint this kind of confusing? i guess this is what the GL and the crankcare rating are for to tell you.

No, the previous explanation was incorrect, or at least incomplete. What you see is that gear oils and motor oils (any hydraulic oils, etc) use different measurements - I suspect that they use different orifice sizes for the tests. 80wt gear oil is the same as 30wt motor oil. In multi-grade oils, the number next to the 'W' is cold viscosity, and the other number is the 100C viscosity.

That being said, the 85W-140 I put in my front axle, even though it should be the same as 30wt motor oil according to the charts, flows like molasses in January...literally.

JayC

 

[284 International]

I'm not sure what was incorrect in the information. I don't know enough to give genuinely complete information, and don't claim to. But the units of kinematic viscosity (essentially how easily a fluid pours) are Stokes. Stokes are Stokes. The data for lubricants are normally listed in hundredths of a Stoke, or centiStokes.

Engine oil SAE 10W-40 [SubsTech]

At 104 degrees Fahrenheit, SAE 10W-40 motor oil measures 108.5 centiStokes, and at 212 degrees Fahrenheit it is 15.4 centiStokes.



Synthetic gear oil SAE 75W-90 [SubsTech]
At 104 degrees Fahrenheit, SAE 75W-90 gear oil is 110 centiStokes, and at 212 degrees Fahrenheit it is 19.2 centiStokes.


The attached chart shows how the ratings correspond again. I don't have a source for it, I'm sorry. The acceptable range for 90 weight gear oil spans from more viscous than 50 weight motor oil's high end at 210 Fahrenheit to nearly as low as 40 weight motor oil's low end. At low temperatures (say, household temperatures) gear oil is definitely thicker than motor oil, but around here, in the summer, spilled motor oil looks about like spilled gear oil; gear oil just stinks worse! :laughing:

I don't want to get the thread off topic, but wanted to clarify and apologize if I didn't do a good job of explaining things.

 

[crazyal]

For my old 2002 Saturn with a standard transmission ATF is the recommended fluid. I haven't got to the point where I need to change the fluids yet but when I do I'll probably go with a synthetic gear oil for the front since SUDT is not cheap and I do you my Kubota in cold weather.

 

[Jerry/MT]

Clemson, it has to do with how the lubricants are rated by the SAE for their purpose (gear oil or motor oil). Here is a chart showing the viscosity differences. At "cold" temperatures, like room temperature, there may be a lot of difference in viscosity between gear oil and motor oil of, say, 80w-90 and 30w. However, the oils are rated at 100C, or 212 Fahrenheit. If you warm the containers up in boiling water, the two lubricants will be the same viscosity. :thumbsup:

I think you maybe misreading that chart. As I understand it,the single weight oils read across to the 40C scale while the gear oils read acros to the 100C chart.