# Hydraulic oil diagnostics



## Judhinho (Jan 4, 2017)

Hello members... my 1996 JD 6400 tractor always got the problem of overheating the hydraulic oil every time it works for more than 1 hr. The cooling system is working perfectly and I changed the oil filter but still the problem has not been solved.But again there is some funny sound that comes out in the main pump. Thanks in advance.


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## stack em up (Mar 7, 2013)

Oil pressure going over relief will cause it to heat up and squeal in the main pump.


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## Tx Jim (Jun 30, 2014)

Ditto what stack stated PLUS is hyd oil cooler & screens spiffy clean???


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## 506 (Mar 22, 2016)

in addition to the above (which are spot on), check the oil level in the sump. Too much oil in the sump will also lead to the condition you are seeing.


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## Farmerbrown2 (Sep 25, 2018)

What kind of oil you got in it ? I had issues with my JD 4020 when I switched to JD oil they went away. I agree with stack if pump is set to high or bypass to low it will heat up in a hurry . When I worked for the demo company on cold days we would make pumps bypass to warm oil up hold both sticks back for 10 minutes and you where ready to rock and roll.


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## Judhinho (Jan 4, 2017)

@ Stack em up, meaning the oil should be over releaf?

@ farmerbrown where exactly is the location of the that bypass switch?

Also what I thought it might also contribute to oil overheating is that the electric wires might be incomplete


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## slowzuki (Mar 8, 2011)

PFC hydraulics - likely leak in a sensing line somewhere. Makes your pump run against the relieve valve heating the oil. I'd bet your tractor doesn't have the usual slight pfc delay to pickup pumping when you use a remote or the loader.

Gauge on the test port likely will show the pump is hammering away at 2900 psi all the time.


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## slowzuki (Mar 8, 2011)

Farmer brown - I think the tractor has the newer style pfc hydraulics than the older jd closed centre systems. Not using a bypass valve but a sensing/feedback line to modulate the pump swashplate angle rather that just on off.


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## Farmerbrown2 (Sep 25, 2018)

I am no hydraulic wizard just trying to help out .


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## slowzuki (Mar 8, 2011)

Wasn't trying to be rude, what you're saying is exactly bang on right for the older deeres and whites with the earlier closed centre hydraulics using a compensator valve to destroke the pump.



farmerbrown said:


> I am no hydraulic wizard just trying to help out .


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