My reservoir is low. I called my dealer and they use Kendall 20w50 in the hydrostats but it is hard to find. They sell it, but my dealer is a good ride away. I picked up some off brand stuff at Walmart to keep it topped off until my first oil change.
Whether synthetic is better oil or not is a matter of opinion. HydroGear themselves said to run "Conventional" in their drives as man00 already stated and who better would know what to run than them/the manufacturer.
Depending on it's application it's use, (synthetic) can be beneficial in colder or hotter temperatures. As far as a drive unit on a lawnmower goes there is no real benefit I can see.
You say Ferris, Gravely and Hustler in their Super Z HD recommend Mobile One 15W-50 and maybe they do and I'll have to pull some PDF files/manuals and check just out of curiosity. Toro also says you can use the Mobil 1 15w50 but they also say if you select that type changing the 15w50 or 20w50 synthetic oil should be done every 250 hrs while the oil they recommend you use can be changed every 500 hrs so I don't think at least for me it's very beneficial to run 15w50 synthetic. I'll stick with what the manufacturer says or recommends.
20W50 is basically air cooled motorcycle oil. If you're having trouble finding it in your area ask the clerks where the motorcycle oil is. Wally World usually has it in a small separate section next to helmets etc. or a very small bottom shelf that's hard to find in the oil section.
Parts stores will usually have it also.
If you can't find it that way but live near a motorcycle dealership you can buy it there but it will probably be more$$
Can I ask you a question ric?Do and use what the manufacturer/ manual calls for, if it calls for a synthetic then use a synthetic if it calls for plain old 20w50 then use it. I ran the 2800 drives for 1400 hours total and used the plain 20w50 and never had an issue. I wouldn't recommend changing viscosity. If your manual doesn't say anything about synthetic then I wouldn't use it.
The best oil $ can buy off the shelf other than Amsoil is Shell Rotella,either the synthetic blend or full synthetic...ill fill my drives up with 15/40 and forget about it.
How do you guys like that!!...lol
You would think a lighter oil would get through faster,the thicker oil would take more force to squeeze through,,but hey it is what it is....I didnt do my change yet,,and have another 50 hours to research it,,Im probably going to go with Royal Purple 20/50 with the extra zinc and phosphorus to be honest.I'm not sure why you run a lighter weight oil. These transmissions use the oil as hydraulic fluid. So ruining a thinner oil would probably create more heat due to thinner oil squeezing by clearances in the trans.