Weak hydraulics when hot

[pulser]

I have a Kubota B7200 4wd with a front end loader and box scraper on the three point. When I first start up, the loader and three point operates ok, but after running for a while, the lift on the both the loader and three point gets really weak and will barely lift a half load of dirt or the box scraper. I checked the filter screen which was ok, and changed out the hydraulic fluid, and this did not help. Seems like the fluid is bypassing, so maybe the pressure relief/bypass is shot? Not sure if the only bypass is on the one on the spool? Can the bypass be rebuilt? Am I on the right track? Maybe the pump is the problem? Any suggestions on how to troubleshoot the problem?

 

[schmism]

I have a Kubota B7200 4wd with a front end loader and box scraper on the three point. When I first start up, the loader and three point operates ok, but after running for a while, the lift on the both the loader and three point gets really weak and will barely lift a half load of dirt or the box scraper. I checked the filter screen which was ok, and changed out the hydraulic fluid, and this did not help. Seems like the fluid is bypassing, so maybe the pressure relief/bypass is shot? Not sure if the only bypass is on the one on the spool? Can the bypass be rebuilt? Am I on the right track? Maybe the pump is the problem? Any suggestions on how to troubleshoot the problem?

if i had to guess it sounds like the pump is shot. A worn pump will have greater than normal tolerances on the pumping parts. (what are tractor pumps, gear pumps?) when the fluid is cold it is more viscous and the pump is able to pump it well. but as it warms up the viscosity lowers and simply "leaks around" the pump because of the larger worn tolerances.

least thats my theory on it