Hi all, I have an 01 sportsman 500ho. Over the labor day weekend I was on a quad trip when it began to over heating on me, after getting home from the trip I tool the radiator out and cleaned it as well as checked for proper flow and it was good. Next I pulled the thermostat and put it in boiling water and it opened like it should, then I removed the water pump cover and pulled the rope and it spun as it should. Fan runs also, I'm out of ideas so any input would be great. Thanx all

 

Notice any leaks at the bottom of the water pump housing drip hole(water pump seal) before you removed the cover to check the impeller? Usually thermostats aren't the problem. Trapped air pockets in the cooling system,clogged radiators especially around the back by the fan. Since you've taken the radiator off and cleaned,established that the thermostat and fan sensor is ok(fan kicking on) I'd lift the front end,leave the radiator cap off and let the fan cycle on and off several times to remove any possible trapped air pockets.This may take upward of 15-30 minutes at times. Wouldn't hurt to replace the 13 psi cap at any auto store. A coolant pressure test may be needed if the machine still over heats.If it wont hold 10 psi you have a leak some where.If it's gotten hot enough a head gasket can blow and leak coolant into the combustion chamber.