I am in search of some information on Mud Hog 4WD system on a 7720 (84). We have had heating problems in the hydro unit since we purchased the used machine. The hydro unit has been replaced with a new one from Eaton and we have had the oil cooler checked and cleaned. The cooling problem only occurs when the 4WD system is NOT in use (road transportation) The Temp sensor has been changed and the control seleniod has been rebuilt. We regularly clean the radiator and I have gone so far as to replace all the foam to keep the dirt to a minimum around the radiator. I am out of ideas and this is not a common system on a combine in this area. The dealers have been at a loss for sugestions so any help would be apperciated.