20,000 Posts & Climbing
Join Date: Jun 2009
Location: Sault Ste Marie, Ontario
Re: Hydro Fluid vs Motor Oils in Transaxles and Pumps
Estimated service life expectancy of a Sundstrand Series 15 hydro is 15,000 hours at pressures not exceeding continuous duty rating and using fluids that meet the Allison C3 or Caterpillar TO2 specifications.
Ambient temperature determines the viscosity required. You can probably get away with 30W oil, I can't due to winter operations at temps lower than -20į F. I use Dexron ATF.
Some find that the hydro whines more with certain fluids, and others have noted a slight improvement or decrease in response between different fluids. The human animal, being as adaptable as it is, can adjust to the minor differences.
Shock loads are not a problem with Sundstrands, the wheels will break traction first. The continuous duty pressure rating is 2500 psi (an iffy pressure to achieve with any GT under anything resembling normal operations), and the peak pressure rating is 4000 psi.
Can it be broken with a shock load? Yes, if it drops off a trailer when traveling down the road. The hydraulic lock caused by the swash plate being in the neutral position when the tires contact the ground at speed will cause instant and severe damage.
Contamination is the reason for changing fluids in a hydro. For all practical intents and purposes, oil doesn't break down at a rate that will cause any issues. Any oil, motor oil, hydraulic oil, ATF, or synthetic. Industry uses the same oils that are recommended for hydros, and they don't get changed for thousands of hours. A six month oil change schedule can mean up to 4000 hours on a 24/7 operation.
Bottom line, if it meets the specs noted above, all is well. Just don't mix types of oil. The additive packages may not be compatible and can cause the system to gum up. Whatever you choose, use the same to top up the system when required.
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