reinstalled used cooler,flushed with calgonite dishwasher soap. pulled thermostat,filled with straight water and put to work in the field. ran for less than 5 min and temp went to 220 deg f. shut down and let cool flushed system again, got out more grey oil sludge. tried again. this time tractor worked for 20 min and over heated. shut down and let cool. reflushed system again, gettin very little sludge. blew air from fan side to front, front to fan side, and fan side to front until no dust or fuss appeared. sent tractor back to field and worked for 6 hours. temp never went over 160 deg f. brought back into yard and reflushed 2 more times with calgonite and 2 times with fresh water. reinstalled thermostat and filled with antifreeze water mix to -50 def f. put back to work for 18 hours. temp never went over 190 deg f, same as thermostat. no oil into antifreeze no antifreeze into oil. I have come to the conclussion that someone sabatoged tractor by putting used motor oil into rad. we have run this tractor for 600 hrs in the last 2 years in hot and cold weather and never any sign off oil in antifreeze thanks to everyone that had input. strange things sometimes things happen. hope this one doesn't again.