Hello all! New to the forums, though I admit, I have lurked around anytime I have issues.

Anyway, I have a 2000 Sportsman 500HO and recently it has developed an overheating problem. It started when my friend noticed the coolant was a little low and decided to add a little tap water to the radiator for me. Anyway, after that, it started overheating on my next ride and ended up bursting a hole in the relief coolant line. Got that replaced and added more antifreeze to the system. It ran for a little bit just fine, kicking the fan on when it warmed up but then a few hours later I took it out again and it started pouring steam out the rad cap. I thought maybe it needed a new rad cap and so I replaced that, same problem still. I hardwired the fan to the battery so it just always runs and it still is pouring steam out the new rad cap. I am thinking maybe just an air bubble or maybe a bad thermostat but didn't know if that sounds right? It seemed like both the top and bottom hoses were warm when the ATV is heated up.

The radiator is clean and clear so it shouldn't be that.

I also have a 2010 Sportsman 500HO that has a very weird issue in that it will be running just fine and then all the sudden bog down and die. It won't start up until an hour or two after which it will fire up no problem and run. There is nothing that makes the ATV bog down specifically. I am 95% sure it is a gas issue, but am not sure if maybe a gas line is to close to an exhaust manifold and is vaporizing the fuel, or if something might be going on with the gas tank venting? I am really at a loss with this one, but it is a bummer since we can't really trust it for a longer ride.

Any thoughts for either of them? Thanks!

 

On the 2000 model I'd leave the cap off,jack up the front end and let the fan cycle on and off several times. You can squeeze the hoses to aid in purging any trapped air. Top off the radiator,replace the cap, top off the recovery bottle and see how it does.Thermostats are not normally a problem,but trapped air is.Best also if you don't have coolant around to use distilled water instead of tap water with all the minerals.A little tap water won't hurt just to bring the level up.
On the 2010 model make sure the tank vent line isn't kinked where it goes into the headlight pod area,and that you can blow back through the line into the tank with the cap off and hear air hiss. If this is ok,you can add extra fuel line foil insulation around the fuel/vacuum lines to the carb and also under the tank to off set any heat that could cause "vapor lock" problems. Plus could be as simple as a little trash/dirt in the fuel filter or fuel pump..

 

I did what you said with the 2000 that is over heating and it still seems like it is pouring steam out the rad cap. How hard is it to get all the air bubbles out? It certainly didn't seem like there could be any unless they are really stuck down there. Would draining and refilling be a better option to do that? Could the water pump be bad and how would I test that? On the right side of the engine there is a high pinging, not sure if that is a normal sound or may be something else going on, or is the water pump/

 

Also the hose coming off the bottom of the rad is cool and the top one is hot when this is happening.

 

Sometimes it takes a while to purge all the air out. Jacking it up at the front or even the side will help purge air along with squeezing the hoses as it runs.If in doubt about the w/p impeller(no coolant flow seen back into the radiator) just pull the w/p cover and check that the plastic vanes on the impeller haven't gotten hot and melted from cavitation and the impeller nut hasn't loosened allowing the shaft to turn and not the impeller. I've found this to happen several times over the years. If all this checks out and it still has problems,it's possible to have a partially clogged radiator that needs a good flushing out.Make sure the radiator area behind the fan shroud and fan is not caked with mud,plus I've found slow leaks in this area that would cause problems.

 

Its not circulating if the bottom rad hose is soft and the top hose is hard. They should both feel the same. Firm and warm.

 

So... Made a little progress, I think.

I tried draining completely and refilling, same problem. After it starts to heat up, it is spitting fluid back out the rad cap in spurts. (See video here)


SO I took off the water pump housing and made sure the impeller is still intact and is moving and the nut hadn't come loose. That all checks out. Where I think there may be an issue is when I put a hose the rad cap and pressurize the system, only the hose coming off the bottom of the water pump housing has water flowing. The top hose only has a small trickle. When I put the water in the bottom hose, the water comes out the rad cap and not the upper hose off the pump, when I put the water in the top hose, it pressurizes until I cannot hold the hose on anymore and no water flows out the rad cap or the lower hose. So to me it seems like the hose going to and through the engine block is not flowing smooth.

Any idea why that might be?

EDIT::

DUH, Thermostat. Forgot about that guy. So I pulled the thermostat. What is the best way to test that thing? Also, if the thermostat is bad, would that in theory, stop the flow of coolant, thus not allowing the fan to cycle and overheating the ATV and then boil the water out the rad cap?

 

If the fan isn't coming on properly it could be a bad radiator sensor,plus there is a 10 amp sealed fan circuit breaker under the front panel that has to have power on each side of the red wire. If it doesn't slice the pouch open and check the connections for corrosion. This circuit breaker is available at most auto stores.Coolant flow won't affect the fan operation. It should come on if the sensor and circuit breaker is ok.Plus you can run 12 volts direct to the fan motor itself to make sure it's working ok.A faulty thermostat (rare for thermostats to go out,but can happen) can stop coolant flow.You can pull the thermostat seal off the thermostat and place it in boiling water. You can tell if the center pin is opening the thermostat to allow coolant flow. You can also just replace the thermostat seal only and test without a thermostat to see if it's the problem or if you have other problems in the system.If you can narrow it down to a faulty thermostat and replace it,make sure the small bleed hole in the thermostat faces upwards. Bleeding trapped air on these models are the hardest since the return hose goes back to the filler neck first,then to the radiator. Polaris didn't change this until the 2005 models when the return hose bypassed the filler neck and went straight to the radiator.. #20 is the radiator sensor.http://www.cyclepartswarehouse.com/f...2000&fveh=5519
#3 is the sealed fan circuit breaker.http://www.cyclepartswarehouse.com/f...2000&fveh=5519

 

My manual says to add the water slowly then shake the atv side to side to help bleed the air out.
Mine over heated do to a air lock and it was pain to get it out. The thermal sensor for the fan is on the lower corner of rad ,so if you have a air lock the sensor will not work until the water is circulating properly. At least mine would not.

 

SO, I bit the bullet and disassembled everything and cleaned the rad out. It had a fair amount of dirt in it but nothing major. I put it all back together, tested the thermostat and it works in boiling water. The fan sensor is good and works when it is gets to the operating temp. So OBVIOUSLY there is no circulation happening. The water pump was turning when I took the cover off and started the machine for a minute and watched it. However if I run the machine without the hoses hooked up to the water pump it spits out some bubbles out the top hose outlet so I am wondering if the mechanical or oil seal are bad back there. I guess I am just fighting a really bad airlock. Could it be a head gasket? Not sure what to do at this point though. Maybe when I am burbing I am not letting it run long enough to get the air bubble out. It usually runs for about 7-10 minutes before it starts spewing out a lot of coolant. Is that long enough? How long has it taken other folks?

Thank you all for the help so far but I am starting to lose hope in this. haha