Tractor Repair: transmission/hydraulicsystem overheating, problem occured, drive cab

Question
Regarding a 2005 New Holland 4 wheel drive cab tractor with 265 hours, model TL90A..
When tractor is used for 8 or more hours, the  transmission hydraulic system overheats to point of vaporizing fluid and melts dipstick seal.
This problem occured at 50 hours and dealer enable to locate problem.  Now, at 265 hours the problem occured again.
Tractor is not normally used for more than 4-5 hours at a time.  Overheating not indicated by any sensor.

Answer
Hello,

  Usually overheating hydraulic oil is cause by the system staying on high pressure demand all the time so that the relief valve is always blowing, which will overheat the oil in a relatively short period of time.  Make sure the rear hitch is cancelling out when it is raised all the way to the top and that the remote levers are returning to neutral when not being used.  On certain machines with a loader, the system can stay on high pressure if the loader is removed and the valve stays with the loader, and the supply and return hoses for the valve are not hooked together.  If this machine has a hydrostatic transmission, there could possibly be a problem there.  I'm sure the dealer would have already checked the oil cooler and verified that oil is flowing through it.  It's unfortunate the problem could not be found when it occured at 50 hours when it was probably still under warranty.