HST Tranny Oil Cooler

Marooned · Dec 21, 2005

I have been reading several posts about Auxillary oil coolers for the HST Tranny. I will be taking delivery of my 4330 HST next week and after reading how the HST trans can get pretty hot during long periods of operation, I was considering getting an oil cooler installed. I have several questions in regards to this:

1. From what I have been reading on these posts, it appears that the loss of a few PTO HP on the HST tranny is due to the heat that is created during use. At least this is what I am reading into it. I'm not much of a scientist and really don't understand this at all. If you could effectively decrease the heat created by the HST, wouldn't this translate into a few more HP @ the PTO?

2. If I were to get an auxillary oil cooler installed for the HST, would this affect my mfg's warranty?

3. If heat is really a problem with the HST, wouldn't Kubota install oil cooler on every HST @ the factory?

4. Has anyone installed one? Does it work well? And what is the approximate cost?

Thanks for any input you may have!

(My main concern here is during the Hot Texas Summer / shredding my pasture. I want to do everything I can to prolong the life of my new "baby"!)

Thanks,
Larry

JRobyn · Dec 21, 2005

Hi Larry,

Welcome to tbn. The 4330 already has an HST cooler. It's mounted right in front of the radiator. I don't think you'll have any heat issues with the 4330. Fine machine!

_RaT_ · Dec 21, 2005

It does indeed already have a hydraulic oil cooler. The Kubota L30 series HST's just don't seem to get that hot. I have tried to overheat it but to no avail.

Marooned · Dec 21, 2005

JRobyn,

Boy do I feel stupid. /forums/images/graemlins/blush.gif
I assumed since people were talking about tranny oil coolers in other posts, that it did not have one.
Thanks.

Larry

rdsaustintx · Dec 21, 2005

( From what I have been reading on these posts, it appears that the loss of a few PTO HP on the HST tranny is due to the heat that is created during use. )

I think you have the causality confused:

The mechanical loss in an HST is inherently higher than a mechanical transmission. 12-15% or so. It's the trade-off for superb speed control with constant engine revs.

The losses are due to various sorts of shear friction, which heats up the hydro oil, plus a little leak-thru.

PTO power reduction and high operating temps are both attributes of HST's. An oil cooler simply helps one of those.

Russell in Texas

_RaT_ · Dec 21, 2005

The losses are due to various sorts of shear friction, which heats up the hydro oil, plus a little leak-thru.

PTO power reduction and high operating temps are both attributes of HST's. An oil cooler simply helps one of those.


I would suggest by helping one of those, namely cooling, it also changes favorably the diminishing return you inherently have when hydraulic fluid gets hot. The really nice thing is that when the tractor is first started to when it is 100 degrees out and the tractor has been run hard, there is no discernable difference in the operation of the HST.

rdsaustintx · Dec 21, 2005

( I would suggest by helping one of those, namely cooling, it also changes favorably the diminishing return you inherently have when hydraulic fluid gets hot.)

NO - I guess I am not being clear. /forums/images/graemlins/frown.gif

The power loss occurs no matter what. A cold hydro actually loses more power than a hot one, as shear friction is a direct function of viscosity, but parts and oil tend to last longer.

Russell in Texas

_RaT_ · Dec 21, 2005

I guess I'm not clear either, overheated hydraulic fluid tends to thin out thus creeping past the clearances easier and what I would surmise would make it less efficient. I only know this from previous tractors. The cold condition lasts for a very short time. I would take a guess my fluid never gets much past 160 degrees based on my ability to touch the hoses and filters and not get to uncomfortably burned. Your right that the loss in a HST tranny will happen regardless as it will in any transmission built but to a lesser extent. Its just that without the cooler there controlling the fluid temperature, the loss would in all likelyhood increase expontentially as the temperature increases beyond a certain level. What that level is is beyond me but I would think anything exceeding a couple hundred degrees could be a problem.

PS, I use a full synthetic hydraulic fluid in my HST and coupled with temperatures in my area that rarely see freezing, get a very consistent operation of the HST.

ns_in_tex · Dec 21, 2005

( (My main concern here is during the Hot Texas Summer / shredding my pasture. I want to do everything I can to prolong the life of my new "baby"!) )

I think the main thing when shredding is to watch the water temperature. If it starts to rise above it normal operating temperature, it probably time to stop & clean the radiator screen.

Marooned · Dec 21, 2005

Thanks to all for the great information.
Once I get the tractor, which should be next week, I plan on running through the winter and see how things go once outside temps begin to climb to the 100 degree mark here in Southeast Texas. I will probably be close to my 50 hour service and can make a decision then if I think I need an additional HST Cooler (as I recently found out that the tractor is equipped with a cooler already).

I'm looking for all the longevity I can get here, because more than likely, this will be my 1 & only tractor purchase. But I've also learned to "never say never".