my rzr 4 800 is overheating. when you start it and let it warm up, the temp. keeps rising. the fan kicks is right away, but it the temp, keeps rising and eventually the computer kills the engine( good looking out Polaris!). I was told by a atv mechanic that the thermostat is seized shut. can that be? or could it be that or the water pump. before this issue I flip the rzr and ended up up side down. I immediately shut the engine off. and flip it right back to its feet! and drove it back to the trailer located like 4 miles away with no issues. later I tried to use it and it started to warm up and the problem began.....what does the rzr community think???? please help!!!!