HST power loss at operating temperature

[browns40]

Hi All,

Actually had an opportunity to do some snow removal last week, which reminded me of something that seemed a bit odd to me about the 3320 I have...

When the motor is at operating temperature, and the hydraulic fluid is still cold/thick (just starting to work) , there seems to be distinctly more power...

I find I need to nudge the tach up 300-400 RPMs higher once the transmission/hydro has had a chance to heat up, to maintain the same speed/power it had when cold.

Is this normal with the loss of viscocity heat brings? I used tractor hyd fluid that met the specification listed, but wasn't brand name...

Are there additives anyone is aware of that can raise hydraulic viscosity? I hate the thought of it, but it seems weird...

Any advice from experienced HST folks would sure be appreciated... I'm tempted to dump it & start fresh, although there's only 90 hours on the current fluid.

Oh:
---No there is no water in the system... fluid still looks/feels basically same as when put in

---Yes, there is a bit of "hydraulic whine" I hear, but always have, even when tractor was new with JD fluisd

Look forward to hearing what the "braintrust" has regarding this one... What a great site! /forums/images/graemlins/grin.gif

Happy tractoring!
/forums/images/graemlins/cool.gif

 

[BGL990]

With the caveat that I don't have any experience with "big" hydrostatic transmissions (just my garden tractor), it sounds more or less normal to me. Hydrostatic drive, by it's very nature, will be sensitive to oil viscosity changes due to the internal leakage always present in hydraulic pumps and motors. A good synthetic fluid would likely help as it won't change viscosity (as much) with temperature changes.

My Sears garden tractor does the same thing. When it gets really hot, there is a VERY noticeable difference in the amount of "go" the hydro tranny has. Unfortunately it is a sealed unit and I can't change the fluid to something better /forums/images/graemlins/frown.gif

 

[browns40]

Thanks BGL990,

I have -zero- experience with HST so I was at a loss for what was happening...

I think I'll do some research on what holds viscosity best with temperature fluctuation and make the switch with the next oil change... sure won't be happening soon with "all" the snow removal hours she's racked up this winter. /forums/images/graemlins/tongue.gif

Appreciate the feedback!

Happy tractoring! /forums/images/graemlins/cool.gif

 

[CT_Tree_Guy]

Hiya Nathan -

We've been having NUMEROUS discussions about hydro fluid in the K****a forum, and the general feeling is that hydros want the best synthetic oil money can buy. There are plenty of people who will tell you that it doesn't matter; that you can use Amalie All-Trac, PermaTran, or anything that says it meets the specs for your particular machine.

My opinion is that given the expense and complexity of a hydrostatic transmission and the superior cold-weather characteristics of synthetics (whether motor oil, hydraulic fluid or an other lubricant), it's a slam dunk, and darn cheap insurance.

We just had a post about a K****a BX-23 hydro tranny that just plain blew up with low hours on it, which is very unusual. The failure occurred during fairly cold weather, and synthetics were not being used. Does this prove anything? No. Does it further encourage me to recommend synthetics in hydros? Yes.

I'd be interested to see if you notice less difference between cold and warm performance with the synthetics.

Good luck, John