02 sportsman 500. Still having the same issue. Temp light is coming on long before the actual radiator is hot. Fan is not coming on. I have put 12 volts to the fan and it works fine. I burped the system and still can't get the lower hose to feel full and hard. I opened the water pump bleeder and just made a mess of the garage floor. Could this just be the thermostat at this point? Clogged radiator? Is there an aftermarket thermostat that will cross with the stock? OEM is to much to change on a whim. I'm getting really frustrated at this point. Quad fires right up and runs fine. HELP ME PLEASE.
Thank you
Paul P.

 

If radiator is clean front and back(no mud) REPLACE radiator thermal sensor #4010161,this is the most common thing that happened on these models! When sensor shorts out,will not send power to fan. I replace dozens of these for the same problem. The other thing could be the thermostat sensor on the left side of the cylinder # 3085352 (resistance can be checked by an ohm meter when cold and when warm the resistance will start to lower if operating properly,NOT usually a problem)Thermostats are not noted to be a problem either,but you can clamp off hose,remove thermostat and test it either with hot water or a heat gun to see if its opening properly.(You can actually remove the rubber gasket from the thermostat and place back on the engine and run it with out the thermostat just to eliminate any doubts,just leave radiator cap off to purge any air!) Either way if you replace the radiator sensor or thermostat sensor and refill radiator,LEAVE the radiator cap off until the fan kicks on,then top off coolant and replace cap. Hope this helps,but 9 out of 10 times its the radiator sensor especially if it overheats and fan doesn't come on!! There is also one electrical thing to check,there is a 10 amp sealed fuse under the front panel,make sure there is power on each side of the wires coming out of it with a test light or ohm meter. Just try to eliminate one thing at a time. OPT

 

Problem is the radiator is not getting hot. Just the fill neck will start to steam and then the engine light will come on. I'm thinking the sensor is not getting hot to turn on the fan.

 

id check erry thing 0PT recommended...but id be real eager to drop your thermostat in a pot of water with a thermometer an see if its working,..dose sound like a circulation issue,...if every thing else checks out ok,..id be lookin at water pump next!

 

Just orderd a new heat sensor that was mounted on bottom of radiator. The wire sheild was burnt and a wire was disconnected. Also notied that the radiator was caked so bad that I had to remove form machine and used water and air presure to clean it up. I tried putting a trouble lite behind it first to see if I could see light, no way it was packed.

 

can get an aftermarket sensor too its a Wells SW-526, last one I did I had to cut [plug off of old one and splice wires to new one, worked fine and was cheaper than oem

 

Mud and radiator sensors,the TWO most common overheating problems on these machines! Glad you found the problem! OPT

 

one more time, I replaced the fan switch. Still no fan. Here is what I discovered. I drained coolant through the sensor hole. replaced sensor and cleaned terminals and used electrical grease. Filled radiator with water as I figured if system was working properly I would see green soon enough. Fired up quad with pull rope as battery was weak. Started first pull no white smoke at all. All was going fine, small air bubbles and then the radiator started to get warm and then I could see the antifeeze mixing in. Then as it got hotter it started bubbling hard and burping out as fast as I could re-fill. Fan never came on, but I was adding cool water to the radiator. Finally gave up as I was running out of water. End of the story is i'm thinking the thermostat is openeing and when it does it is leaking from the head gasket and blowing back into the cooling system. Does this sound about right? any other possible solutions? Maybe? If not does anyone have the procedure with torque specs? I'm no stranger to the garage, raced MX for 20+ years and turned my own wrenches every weekend. Bikes are open and easy to get at. Not these big heavy boxy things. I'll learn could just use some guidance. OPT, Thank you for all your support so far. Wish I could buy you a beer or 2 and everyone else who helped
Thank you

 

You can try to eliminate thermostat by just using the gasket that slips around the thermostat and placing it alone back into the housing,Then replacing cover and hose. Then see if it does the same thing. If it still bubbles over with a new sensor,thermostat out,radiator cap off,then it could be a head gasket OR a internal stoppage area on the radiator(not uncommon) Also check your oil to see if coolant is getting in it. PLUS IF battery is LOW (having to pull start) may not have enough power for the fan?? Has to have a good battery for fan to kick on. PLUS have you ever checked the water pump impeller for damage and not circulating properly?? Have found impellers that were broken,slipping on shaft,or fins just melted on plastic impeller. OPT

 

I checked the thermostat lasnight and all was fine there. Started it up and NO white smoke, NO contamination in the engine oil. Going to check the waterpump next. I did ask at the dealership and they stated that they would be surprised in it is a head gasket as the have only sold 2 of them in 6 years. They did the water pump seal and wondering if they may have not tightened the inpeller. I have no problem with replacing the head gasket, but would hate to go that far if not needed. The lower hose still doesn't feel full. When I replaced the thermo sensor at the bottom of the radiator it flowed out without problem. Is it possible there is a blockage in the rad? Engine hot rad cool.