I am one of those on this thread that get flak from others over not using K branded lubricants and filters especially the SUDT hydraulic fluid. To ease my mind on this I undertook some research. The following paragraphs are a condensation of 2 hours of highly technical one on one discussions and another 2 hours reviewing internet and printed data perusal.
K has 2 products SUDT and SUDT2. As far as I can determine from my dealer and Ks literature the SUDT was formulated for low temps as a companion to Winterized diesel fuel and 5-20/30 motor oils. SUDT is their standard for above 20 degrees F. Another extrapolation is when you get below 0 you need to consider heating all those products until operating temps are reached. That is what the military does in the arctic and Antarctic.
I have extrapolated from the information available that SUDT is a product formulation that is proprietary to Kubota. It is a multi-viscosity product that approximates 5-20 motor oil. It is not a synthetic product as some have alluded, it is simply a petroleum based product with additives directed by Kubota to their supplier. Apparently K wasn't selling as much of their above market price UDT (which was pretty universal) so they decided to have something that other blenders could not duplicate due the copyright and patent laws. That is why there is no standards of comparison in their manuals or recommendations and their refusal to condone any substitute product. No other blender can use the term SUDT in their specifications.
SUDT is blended for K by Valvoline Corp. Their technical department will run you around in circles if you try to discuss the properties of the product. Their stock answer to a direct question is "we cannot discuss the product due to our exclusive contract with K". In reviewing their product line they have several heavy duty, multi-viscosity hydraulic fluid products. None are recommended for temperatures below 10 Degrees F, based on cursory review only, not conclusive.
I discussed the product I use, NAPA 85-405, with their blender Martin Petroleum. 85-405 is what they recommend as an equal product to Kubota SUDT as they have no standard for comparison except operating parameters. They do not recommend their Extreme line for that service. 85-405 is a multi-viscosity oil with various additives for all the reasons K has in their literature. They do not recommend it for temps below 10 degrees F. This years extreme cols in the north and east has convinced them they need a cold weather product and they will have one on the market for next winter. it is under testing now. They told me their are only 4 producers in the world for the additives and all blenders use them. Naturally , their contention is K's SUDT cannot have any magic ingredient that makes them unique.
Standard oil and others also makes a synthetic product considered comparable but it is even more expensive than K SUDT.
Conclusion for me: I feel comfortable with my product choices especially as I have 1000 HRs on my
BX25, have always used 85-405 since the 50 mile service when I found the Hydraulic oil contaminated and changed it and the filter then. After thwe switch I noticed no change in the performance or the noise level of the system. The HST has always had a low level whine which increases with RPM. Also I seldom work mine at more than 2500 RPM and usually around 2200. Yes, I change fluids more often than most but I work it hard and long plus here in the NW water contamination is always a problem when a lot of the time we are working in 100% humidity and a lot of moisture goes through the ventilation of crankcase and HST. We do not have the cold temps most of you experience so that is mot a problem. We had 10 days of temps below 20 degree F and I noticed no problems with the 85-405 or standard #2 diesel. I have also stayed with using it in the front axle. 90 W gear lube would have been pretty stiff on those cold days.
I know this is ling winded but I tried to be comprehensive. I find no fault with brand conscious folks, it is their dollar to spend as they see fit. We all have to make, hopefully, informed decisions on our own minus any hype by slick advertising. Mine is based on $ and proximity to the products and now experience. maybe I will know better when I get 5,000 HRs on my BX. That's about when I may decide to trade or no longer be operating.
Ron
