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 | kubotaguy
Join Date: Nov 2003 Posts: 360 Shepherdstown, WV 
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2004-05-17 86205
I was mowing some tall grass the other day with the 60"MMM with my 7800 and I was wearing shorts and could feel heat coming from under the tractor. It didn't burn me but it didn't seem quite right. The when I finished and went to spray off the mower deck I hit the rear end with some spray and it turned into steam. I couldn't touch the rear end with my hand it was that hot. I was finished for the day so I put it away. I got it out the next day and it ran fine. The tractor has about 80 hours on it and I did the 50 hour maintenance. The grill and screen in front of the radiator both were clean. The brake was not set, the fluid level was fine and the temp. guage was not reading hot. Although it was very hot and humid outside when I was mowing and I was mowing very slow in medium range and then went down to low range. Any ideas????
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York 
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2004-05-17 86228
I could think of a lot of things until I finished reading that might be wrong but with what you were doing you are fine. I'd watch the situation but not worry unless you can find out exactly what it is. ....
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 | beagle
Join Date: Jan 2004 Posts: 1333 Michigan 
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2004-05-17 86232
I'm a little surprised with Art's answer, but I guess that's good news. I mowed all day with my 7800 on Sunday, and although I never really checked, I didn't notice any heat from the rear end. The mower deck would load the engine hard, but shouldn't load the hydraulic system or the Hydro. I did mow in Low Range.
So I can keep my eye on my 7800, when you said the "rear end" was hot, was it the Hydro, Gear Case, or Differential Case, or maybe all of the above? If it wasn't for Art not being concerned, I would have guessed there was a possible problem with the hydraulic cooler circuit. I'll keep an eye on mine and see if I get any heat build up. ....
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 | oneace
Join Date: Mar 2004 Posts: 1490 south central pa
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2004-05-17 86234
From what I've seen in the past is some body mistakenly knock the remote valve in to the locked on position and caused the fluid to dead head through the relief. That will heat up fluid fast in fact in the shop we do that in intensionaly to get the fluid to normal operating temp. But you may or may not have a remote valve and if you do you will most likely not not have a detent to lock it to the on position. So I'm just rambling again. Any way if this continues try changing the hydro filter again. Then if that does not work get your dealer to flow test the unit to make sure there is not a relief valve sticking some where. ....
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| hardwood
Join Date: Dec 2002 Posts: 3583 iowa
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2004-05-17 86240
Hydros will run quite hot under heavy drawbar load, but if you were only mowing with a MMM it should'nt get hot enough to produce steam. I agree with what has allready been said about a remote valve being in a position to run fluid back thru the relief valve, that will cause lots of heat buildup fast. Another thing I thought about is the possibility of a hose being kinked off or a line that has been crushed that feeds the hyd fluid radiator in front of the engine radiator to cool it. I know basicly nothing about Kubotas, but I'd assume every mfgr. uses a fluid cooler on their hydro tractors. Frank. ....
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| kubotaguy
Join Date: Nov 2003 Posts: 360 Shepherdstown, WV
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2004-05-17 86248
Thanks for the replies fellas.
Beagle, I have mowed with my 7800 several times and it has never gotten that hot but then again this was some pretty tall and thick grass. When I said the rear end was getting hot, I was trying to spray the grass off the two wheels behind the mower in the middle and the water when up on the rear end and steam started coming off like crazy. Then when I got on the tractor to hook up the loader and put it away, I could feel the heat coming from underneath.
Oneace, you bring up another interesting point that I had a question on but forgot about. I have been taking my loader off to mow with and on the loader joystick piece that stays with the tractor there is a little lever that has a lock and unlock position. I've always left it in the unlock position. I can't find anything in my book about it. What is that lock and unlock thing for and could that be the cause of the problem.
On a positive note, I had it out a little bit this evening and everything seemed fine with it. ....
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| beagle
Join Date: Jan 2004 Posts: 1333 Michigan
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2004-05-18 86276
That lock lever on the loader valve will lock out the joystick so you can't accidently bump the loader. It doesn't do anything hydraulically. Just thinking through this a little further, it sounds like you ae getting good cooling with the loader on, but might have a circulation problem with the loader off. The rear end should not get that hot from mowing, there just isn't a lot of load on the hydrostat from mowing. Have you noticed any heat build up with the loader? Maybe we can narrow down where the flow restriction might be, if there is one. Any chance you accidently left the loader joystick in the float position while you where mowing? If this happens again, check the hydraulic cooler coil behind the radiator. If it is cool, and the hydrosat is hot, there is a circulation problem somewhere in the system. ....
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2004-05-18 86277
All of our hydro.'s, including mine at here at home, will do exactly the same thing under load.
The problem seems to be that to do PTO work, like cutting grass, the engine must be running at 'PTO speed' but the tractor is moving forward at a relatively slow speed, that means the hydro pump is going flat out, but the excess flow is just cycling throught the reservoir heating everything up.
That heat is part of the losses I was talking about in the other thread about HST vs. gears.
Best of luck. ....
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 | jonathanengr
Join Date: Sep 2003 Posts: 100 Bostic, North Carolina
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2004-05-18 86280
I'm glad to see a post on hydros... I have a question, too. Exactly how much noise should a hydro make??? My Dad has a 3130 FST, and when driving my 3430 HSTC said he was unnerved by all of the noise the tranny made. It does make quite a bit more noise--especially the slower you go.
Is all this noise normal? It just sounds very "strained", and since I've neevr been around them I didn't want to take any chances! ....
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| beagle
Join Date: Jan 2004 Posts: 1333 Michigan
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2004-05-18 86287
This is my third hydrostat, all different manufacturers, and all have been whiners. The Kubota is actually a little better than the last two, but it is definitely a whiner. Just make sure you keep the fluid and filters clean and full.
Murf, shouldn't the overcharge fluid from the hydrostat still be circulated through the cooler? ....
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| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2004-05-18 86295
There is no doubt that the HST is a lot noisier than the GST unit, even with the additional noise suppresion of the cab.
Beagle, all fluid does go through the oil cooler as part of the hydro. circuit. Even with this the heat generated is substantial. Considering that the hydro. 'cooler' and the rad. are stuck together, even though the cooler is in front, the temperature of the cooler isn't going to be much less than the rad. and I'm certainly not going to put my hand on that after working the tractor for a while. In fact it was kind of interesting that during the winter when I was plowing snow with my tractor I actually gained heat in my shop by parking it back inside afterwards. The heat given off by the tractor more than made up for what was lost opening the door twice.
Best of luck. ....
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| beagle
Join Date: Jan 2004 Posts: 1333 Michigan
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2004-05-18 86301
Makes perfectly good sense about the temp. at the radiator. I'm going to keep an eye on mine the next time I mow. Thanks ....
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 | DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2004-05-18 86303
Also, consider that the oil in your engine crankcase can easily exceed 400 degrees F, and the oil is designed to take such temps. ....
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 | yooperpete
Join Date: Jan 2004 Posts: 1413 Northern Michigan
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2004-05-18 86313
That's warmer than I would feel comfortable operating at. Would definitely keep an eye on it. Not sure, but running in low range rather than mid range may keep it cooler due to less flow restriction. ....
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| oneace
Join Date: Mar 2004 Posts: 1490 south central pa
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2004-05-18 86328
normal operating temp for most hyd. systems is about the same as the engine normally 175 to 195 on others it is above 200 and some below 175 ....
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| yooperpete
Join Date: Jan 2004 Posts: 1413 Northern Michigan
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2004-05-19 86351
I checked a can of International Hy-Tran fluid last night and it said 200 degrees max. temperature. ....
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