2000 Polaris Sportsman 500, overheating, and blowing out coolant from radiator cap. Fan works fine. Remove cap, and water, coolant, constantly bubbles. Rev the engine, and sometimes it will blow right out the neck. Pump is OK. Thermostat works fine, fan goes off & on properly. I suspect a blown head gasket, or maybe a cracked head. Does anyone have any other ideas? Thanks in advance for your interest.

 

Welcome to the forum.. Raise the machine up with both front tires off the ground,cap off and see if it helps get rid of any possible trapped air. You can squeeze the hoses also as the manual recommends to help with this. May take several times as the fan cycles on and off if this is the problem. If this method doesn't help,no visible leaking noticed,then I'd try a cheap 13 psi radiator cap. If this doesn't help,then sounds like you need to pressurize the radiator to about 10psi and check for any drop. Also check the exhaust for any sweet coolant smell. Could possibly be a small head gasket leak if everything else is ruled out.Plus one other commonly overlooked item is dirt/mud behind the fan shroud on the radiator. I've had them look clean,but had to move the radiators on some to get caked mud off so they could cool properly.

 

Welcome.

 

Thanks OPT for your input. I fairly sure I have the system completely burped. I have even opened an old thermostat, removed the spring & plunger so there is flow without waiting for the thermostat to open. I also inspected the pump, and it shows no signs of problem. There are no external leaks. While the hoses were off the pump, I flushed the radiator & lines, and there appears to be good circulation. The bubbling is constant, and increases, with increase in RPM. A quick rev, results in a blowing out of coolant, with the cap on tight. What do you think. By the way, the machine is ridden in the mountains, on forest roads, and has never, to my knowledge been in severe mud conditions.

 

Then I'd just run a pressure test on the radiator and you should be able to tell real quick if the cooling system can't hold at least 10 psi without leaking down.

 

I'll do it in the AM. I'm betting it will leak down right through the head. I'll let u know. Thanks for your imput. Jim