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748h hydraulic overheating

Started by Hunterlowman, May 19, 2023, 03:14:40 PM

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Hunterlowman

I have a 748h that currently overheats the hydraulic sitting idle. We've changed pump and the filters on it. After we put new pump on it seems to cool down when working it (blade and grapple). Really just needing some help figuring this out. Asked John Deere and they said it was the main pump so we replaced it. Didn't fix a thing 

Wlmedley

I've never worked on your model machine but had a Komatsu dozer that heated hydraulic oil when not working hydraulics and on it pump was staying stroked up in neutral causing unloading pressure to be high.If your machine has a variable piston pump this might be something to check.
Bill Medley WM 126-14hp , Husky372xp ,MF1020 ,Homemade log arch,Yamaha Grizzly 450,GMC2500,Oregon log splitter

Firewoodjoe

I was doing a quick search for you.
Did you use a heat gun to see where heat is and isn't? Are you sure it's hot and not just a gauge problem? Hydraulic oil cooler clean?  Hydraulic oil cooler bypass valve stuck? Some have a hydraulic cooler pump. Just throwing ideas out there. I'd be checking heat starting from the pump itself. Trace it. Pull lines going to and from cooler to be sure it's getting oil.

kiko

Quote from: Wlmedley on May 19, 2023, 05:52:03 PM
I've never worked on your model machine but had a Komatsu dozer that heated hydraulic oil when not working hydraulics and on it pump was staying stroked up in neutral causing unloading pressure to be high.If your machine has a variable piston pump this might be something to check.

Right on the money^^^.  It is a variable piston pump.  The circuit goes as such,  flow from the pump goes to the steering priority valve , though the priority, two exit ports to steer valve and main control valve. Return flow flow through cooler to tank. If the main relief on the inlet is set or operating below the Pressure override on the pump, the pump will stay at angle. Often when the pump is staying at angle it will release when moving a hydraulic function and load back up when you stop. I would open up, clean and locate each of components and from cold monitor which component heats first.

Hunterlowman

Quote from: kiko on May 19, 2023, 06:24:40 PM
Quote from: Wlmedley on May 19, 2023, 05:52:03 PM
I've never worked on your model machine but had a Komatsu dozer that heated hydraulic oil when not working hydraulics and on it pump was staying stroked up in neutral causing unloading pressure to be high.If your machine has a variable piston pump this might be something to check.

Right on the money^^^.  It is a variable piston pump.  The circuit goes as such,  flow from the pump goes to the steering priority valve , though the priority, two exit ports to steer valve and main control valve. Return flow flow through cooler to tank. If the main relief on the inlet is set or operating below the Pressure override on the pump, the pump will stay at angle. Often when the pump is staying at angle it will release when moving a hydraulic function and load back up when you stop. I would open up, clean and locate each of components and from cold monitor which component heats first.
I took a temp gun and basically checked everything and the only thing getting hit was the pump but I will check the steering valve that's probably the only thing I haven't checked. The cooler was working good the fluid coming from the tank to pump and back was all good I'm thinking maybe the sensor might be bad or the steering valve. 

kiko

What pressure do you have the pump set at? 

Firewoodjoe

If only the pump is hot and not the cooler then something is up. And what temp was the pump with the thermometer? 

Hunterlowman

Quote from: kiko on May 20, 2023, 02:53:36 PM
What pressure do you have the pump set at?
Never messed with the pressure stock from the factory 

Hunterlowman

Quote from: Firewoodjoe on May 20, 2023, 03:48:49 PM
If only the pump is hot and not the cooler then something is up. And what temp was the pump with the thermometer?
That's what's got everyone confused the cooler wasn't hot at all. The pump would just keep climbing Made it up to 207 before I shut it down 

kiko

From here it sounds the pump is trying to move fluid even when it should not be. You mentioned it seemed to cool down some when working the hydraulic functions. If the pump pressure setting is above that of the main relief on the control it will heat. A pressure gauge would be the next step. Rarely have a seen a replacement pumpbe set correctly from the factory.   The pressure check port is located at the hydraulic control valve where the pressure hose from thebpump enters. The main relief has likely failed. It is located in the inlet section.

kiko

Also the parts lookup shows a serial number break with different hydraulic pumps.  The pump that you have, does it have a rectangle block bolted on it ?  Does it have an electronic solonod on the pump?

Hunterlowman

Quote from: kiko on May 21, 2023, 09:20:18 PM
Also the parts lookup shows a serial number break with different hydraulic pumps.  The pump that you have, does it have a rectangle block bolted on it ?  Does it have an electronic solonod on the pump?
It's black bolt on no solenoid 

kiko

OK so on the end of the pump controller there is an adjustment screw. That is where you set the pump pressure.  If you get a Guage I can walk you through the set up procedure,  are at least determine whether the issue is in the main relief.  This is a closed center system. So when there is no function called for thus  no flow the pump will de stroke but maintain 3100 psi. Any flow down stream( control valve activated,  a spool leaking,  or the main relief venting below the pressure setting of the pump ) will cause the pump angle to increase. So if the pump angle produces more flow than than can be consumed it will create heat.  Hope I am not over explaing. 

Hunterlowman

Quote from: kiko on May 22, 2023, 09:34:38 AM
OK so on the end of the pump controller there is an adjustment screw. That is where you set the pump pressure.  If you get a Guage I can walk you through the set up procedure,  are at least determine whether the issue is in the main relief.  This is a closed center system. So when there is no function called for thus  no flow the pump will de stroke but maintain 3100 psi. Any flow down stream( control valve activated,  a spool leaking,  or the main relief venting below the pressure setting of the pump ) will cause the pump angle to increase. So if the pump angle produces more flow than than can be consumed it will create heat.  Hope I am not over explaing.
I talked to John Deere this morning they are saying it sounds like the cooler is blocked told me to put the two lines together and see if it runs any cooler. If that don't work I'm going ti get pressure gages and check it 

Firewoodjoe

You'd think the line going up to the cooler would be warming up. At least from heat transfer. But prolly wouldn't tell much. Kinko I'm learning myself every time you type. Woods equipment always has a heating problem that needs chased down. I'm trying to soak all I can in. 

Wlmedley

I believe Kiki will point you in the right direction.Cooler shouldn't be needed much in neutral. I don't know enough about your machine to help much but I believe he does.
Bill Medley WM 126-14hp , Husky372xp ,MF1020 ,Homemade log arch,Yamaha Grizzly 450,GMC2500,Oregon log splitter

Wlmedley

Sorry Kiko ,spellchecker changed what I typed.
Bill Medley WM 126-14hp , Husky372xp ,MF1020 ,Homemade log arch,Yamaha Grizzly 450,GMC2500,Oregon log splitter

Hunterlowman

Quote from: kiko on May 22, 2023, 09:34:38 AM
OK so on the end of the pump controller there is an adjustment screw. That is where you set the pump pressure.  If you get a Guage I can walk you through the set up procedure,  are at least determine whether the issue is in the main relief.  This is a closed center system. So when there is no function called for thus  no flow the pump will de stroke but maintain 3100 psi. Any flow down stream( control valve activated,  a spool leaking,  or the main relief venting below the pressure setting of the pump ) will cause the pump angle to increase. So if the pump angle produces more flow than than can be consumed it will create heat.  Hope I am not over explaing.
Checked cooler nothing wrong with it. I turned the adjustment screw all the way out and the pump was still getting hot just took longer I'm officially stumped trying to get boss to get some gages so I can hook those up and see 

fluidpowerpro

When you installed the new pump, did you fill the pump case with oil before starting? If you didn't that can damage the pump. Check how much flow you getting out the case drain line. If the pump is bad, you will get a lot of flow out of that line. 
Change is hard....
Especially when a jar full of it falls off the top shelf and hits your head!

Hunterlowman

Quote from: fluidpowerpro on May 23, 2023, 04:03:33 PM
When you installed the new pump, did you fill the pump case with oil before starting? If you didn't that can damage the pump. Check how much flow you getting out the case drain line. If the pump is bad, you will get a lot of flow out of that line.
Yes filled both holes to the top. I noticed yesterday it seems to be getting hot on one line. The line that goes from the top to the filter housing 

backwoodsdave

I've found grapple cylinders leaking internally causing this problem, when a grab of logs is picked up and the grapple latched in the close position the cylinder leaks internally and caused the pump to stroke and create heat at the leak inside the cylinder, also some have a habit of latching the grapple closed while going back for another drag or when they sit still, it'll overheat like crazy, hang the open grapple in the air and see if it drifts closed, just something to check.

kiko

^^^^^  that is an example of leak downstream of the pump .  Since the grapple clyninder were brought up, there is a hydraulic swivel for the grapple that could be leaking port to port as well.

fluidpowerpro

So your saying that the pumps case drain line returns to tank through a filter? If so that's typically considered a bad design. Case drain lines should go directly to tank with as little back pressure as possible. Too much case pressure causes the piston shoes to lift off the valve plate causing higher internal leakage and heat.
Change is hard....
Especially when a jar full of it falls off the top shelf and hits your head!

Hunterlowman

Quote from: fluidpowerpro on June 02, 2023, 09:24:57 PM
So your saying that the pumps case drain line returns to tank through a filter? If so that's typically considered a bad design. Case drain lines should go directly to tank with as little back pressure as possible. Too much case pressure causes the piston shoes to lift off the valve plate causing higher internal leakage and heat.
Little update for everyone he bought a rebuilt pump the first time and we took it to a professional after taking it off the pump was shot took the original pump to the same guy it was shot to everything was messed up on the inside. My boss finally bought a brand new pump and hopefully it fixes the problems 

kiko

Thanks for the update, we don't always get those.  Those Oil Gear pumps are hard to repair, they don't have a replaceable valve plate , simply uses the head machine surface as the valve plate. I have had success milling the head and cylinder block to repair.

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