Ok, so I got all the fluids swapped today. No real difference in sound on the engine oil, as to be expected. But it sure runs nice and smooth!
Hydros, however are a different story! The Hydro-Gear OEM fluid was nearly silent; almost no whine at all while it was in. The Amsoil, even though I never had anything but fine performance from it, always had a fairly loud whine, much more noticeable than OEM. I even bled them multiple times to make sure it wasn’t trapped air. I kinda chalked it up to broken-in hydros, since this is my first ZT. However, after putting the Tractor Life in and moving the levers only 4-5 times to bleed them, the hydros are nearly silent again. The whine is gone, even though the filters are the same and the hydros now have many more hours on them since new. I did note for the 2nd time that my ZT-3100s take nearly 2 quarts less than what the internet says… about 3.25 quarts; the vent plugs are weeping and the reservoirs are happy, so not sure where that discrepancy is from.
I don’t know what causes whine in hydros (anyone know for certain? Entrained air?
@Pablo have you heard any similar comments re: Amsoil Hydro Fluid?) but the HPL is almost identical in sound signature to the Hydro-Gear fluid.
Not knocking the Amsoil since it did a fine job, and came out literally looking as clean as it did when new. I was amazed at how clean the fluid was. Guess the $14 Wix SL10102s didn’t have much to clean up!
I’ll check back in another 150 hours and see if the HPL fluids were worth it!