a 961 I bought had an over heating problem. it would get up to 250 and still climbing and blow antifreeze out the radiator so I started flushing it out using mean green to help. flushed it 3/4 times. when it was cooling down I started power washing it. developed another leak, got a new hole in one of the freeze plugs. removed it and got a lot of gunk out that hole. replaced it and re flushed again. made sure I removed the temp thermocouple so it would drain any material in there. after several flushed. finally I got it to hold at 225 running pto speed for 20 minutes with outside temp 88 degrees. I think the block is s clean as I can get it. I do believe who ever had this tractor used stop leak in it. so I ordered a new thermostat, bought a new radiator off ebay for 150 bucks that came with both lower radiator hoses (used to one for my tractor, upper hose, radiator bolts and pads so now she runs around 170 on a hot day at pto speed. put all new gauges on it now I am in the process of sprucing her up. plan on putting my finish mower on it. narrow front with power steering that starts easy and runs great, like new tires on back. good luck on fixing yours. hope all goes well with that.