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post #1 of 4 Old 05-09-2019, 07:36 PM Thread Starter
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Question Hydro Fluid vs Motor Oils in Transaxles and Pumps

These questions are for usage in a mower(s) that use the Sunstrand type15 pumps systems.

John Deere
Cub Cadet
Sears
Wheel Horse
Montgomery Wards
Others so equipped?

Is there a benefit or absolutely no difference when using a motor oil(Rotella T1 30wt) compared to using hydro fluid in one's transaxle system that uses the Sunstrand pumps?

Is one higher/lower viscosity than other?

Would one be quicker/better in system, to prevent damage from not being able to keep up with constant changing loads and gear shocks of forward/reverse?

Does hydro fluid break down sooner or hold up as well as engine oil?

Mower only used in grass cut season. No Winter usage if this makes difference.

I know people say keep using what you've been using, as it won't hurt anything, but the question is, is really using one better for system over the other?

If using Rotella 30wt oil ok to continue use, OR would going to a Rotella Synthetic 10-30/15-40 be better in your opinion.

Thanks
Del
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post #2 of 4 Old 05-10-2019, 03:17 AM
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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 -20 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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post #3 of 4 Old 05-10-2019, 08:05 AM
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Re: Hydro Fluid vs Motor Oils in Transaxles and Pumps

Its all about viscosity. My experience is mostly industrial, but I have many Hydraulic GTs. Mostly I use standard AW32 or 46, because I get it for free. I have tried ATF for better winter performance, with good results, and will use synthetic for even better winter performance. Synthetic oil seems to slip better, even though the viscosity is rated the same as dino oil. Oil life is proportional to the amount of heating of the oil, and of course contamination. When oil in hydraulic systems break down, it smells acidic. I have open 20 year old systems and the oil is fine; and one year old systems and the oil is burnt. The worst contaminant I've found in mobile equipment is water condensation. If you don't use the machine enough to warm the oil and "boil" off the water, you should change the oil just to remove the water contaminant, (why I use the free stuff, lol).

Bottom line; most my tractors are 40 years old, some have original oil (at least when I got them), I suspect they could last many more years. Just make sure the Sundstrands have oil, and its not milky (water contamination).

PS. As I mentioned above, I bought and will use synthetic oil for one of my winter tractors, I think its a good choice. I will report when I have used the tractor for awhile but its waiting for a repower.

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post #4 of 4 Old 05-10-2019, 05:40 PM Thread Starter
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Re: Hydro Fluid vs Motor Oils in Transaxles and Pumps

Thanks guys, you've really helped put my mind at ease.

I'm getting some whine from hydro system, so I think I'll go to a synthetic oil(for transaxle/pump system only) after this season is over. Had a leaking hose before mowing season started, so needed a new hydraulic hose line made, along with fresh oil and filter changeout due to draining system to r&r hose, so I'll wait till about November when I park this beast and do my winter maintenance on it for following cut season.. I mow about 5 acres a week, so this 1990 piece of iron/steel gets a good workout.

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