Hi everyone, I inherited a polaris 400 about a year ago. Last time I took it for a ride up north the headlights gradually got dimmer and dimmer until it stalled out. I used the pull starter to get running again. The next day I pull started it again and went for a short ride and noticed the engine was overheating...coolant bubbling out of overflow. Went and got new battery, still overheats. Got it home and jumped the fan directly to a battery...it works fine. I learned from the forums here to replace the heat sensor that plugs into the radiator (autozone model), so i did that. I did have to splice the new sensor to the original connector since the new one was not compatible. I refilled the radiator with coolant and did my best to purge all the air. STILL OVERHEATS and the fan still does not come on. Is it air in the radiator or bad waterpump. If waterpump, where is it and how hard to replace. The new battery is now dead from sitting all winter, would another new battery cause the fan to run? Any advise would be appreciated, thanks.