Cub Cadet transmission/hydraulic fluid

[esox07]

Guys, I have a CC 3165 (1998-1999 model year) that I picked up second hand. From what I understand, it is BDU-21L transmission. I need to fix a slow leak in the transmission so, I am going to wind up draining it, fixing it and then I will want to refill it with fresh. So, I am not paying $20 plus per quart for the recommended CC stuff. It is 25 years old and has 430 hours on it. I don't want to do something that will trash it, but I am not paying $100 to refill it with CC fluid either. I am looking at mostly summer time (Wisconsin) use at this point. When I picked up the mower, the original owner actually had to add fluid just to get it to move since it had mostly leaked out. He put in a quart of regular ATF oil and said "it is the same thing". I think he had been using that for a while.
So, I have asked some on other forums and gotten responses like Shell Rotella 15W40 diesel oil to 10W30 regular automotive oil, to ATF fluid and others.
This is for the Hydrostatic transmission in the 3165 which also runs the power steering and deck lift from what I understand. This is not for the motor.
So, are these all valid replacements for the factory recommended CC fluid?

Unless I am told otherwise, I will probably go with the Shell Rotella 15W40 Synthetic diesel oil.
https://www.walmart.com/ip/Shell-Rot...sRedirect=true

Is this also an option? It states: "Meets Case / IH (HYTRAN B-6) requirements"
https://www.farmandfleet.com/product...lic-fluid.html

What about just regular ATF:
https://www.farmandfleet.com/product...ion-fluid.html

What do you guys think of those three options? Am I making a mistake with either one? Do you have a preference?

Thanks for you help.
Bruce

 

[cptbarkey]

I found this from google. It sounds like the information you found was correct and the transmission isnt that picky. I recently poured a quart of 5W40 into a T46 and it has been fine for the last 5 engine hours.

https://www.hydro-gear.com/wp-content/uploads/2022/05/BLN-50327_P6.pdf

Page 17

 

[gman2304]

I’ve used Mobil1 15w50 in my 1998 TT K61 hydrostatic since new. Quiet as a mouse after 25 years.

 

[spk2000]

I used to use Mobil1 15w50 in my Snapper tuff torq K57. I have many large hills and it would break down in about 2-3 months. I switched to Amsoil Hydraulic fluid it's 20w50 and it's been going strong for at least 3 years now. I can only get about 50 % out so it wasn't a complete fluid exchange either. Far superior heat resistance

 

[JTK]

Back around 2005 when I owned my cub 2544 rider that also had a HG BDU series drive that drives the Cub cast iron trans axle I researched the expensive Cub Cadet Drive System Fluid Plus. I'm not sure it's even called that today. At the time I even had a correspondence going with someone from hydro-gear. He couldn't give me all the details, but the cub fluid was basically Shell Rimula 15w40 and any name brand 15w40 is all you need for this type of Cub drive system.

 

[Bighorn2500]

Over on Cub forum they’re saying the service manual indicates 20w50 for normal operation, 10w40 for colder climate operation, and synthetic 15w50 as an all climate/extended drain capable alternative.

If it were mine and I intended to keep it for a while Mobil 1 15w50 is what I would be buying.