2004 Sportsman 400 overheating

Removed thermostat
Fan does turn on and off automatically. Disconnectedthe thermal switch and fan runs nonstop
Flushed the system
Cleaned the radiator
Still overheating…..any suggestions

 

Is the coolant flowing? When you flushed the radiator was it clean? Did you pull the radiator out and flush the cooling fins? We just did this to our 400 and I was shocked how much mud was on the backside of the radiator!! I also went threw and straightened a LOT of the cooling fins. Very easy task - just takes patience!!

I would check your water pump next...

 

Depending on which model 400 you have, you either have a sensor in the radiator that can go bad or an ecm module that controls the fan and was under the recall,plus even the replacements gave some problems. Huge ATV Recall by Polaris - Sportsman and Scrambler
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I have a model: A04CH42AS. I goggled it and it is on the recall list. I remember when I first purchased my ATV and had it in for service the dealer said he replaced a part but if I remember correctly it was a voltage regulater but that was 9 years ago...lol...memory isnt as good as it once once. Is a voltage regulater concidered a ECM?

The fan seems to be working properly it will turn on and off when the quad is running and when I disconnect it from the thermo switch it runs non-stop.

Is there anyway to test the sensor in the radiator or the ecm module?

Thanks for the help

 

Well if the fan is kicking on and off like it should then you eliminated that problem. If it was ECM or a rad thermal senor would the fan just not work period.

Make sure its not a air lock. When the ATV is warmed up the top and bottom rad hose shold be both firm and warm.
If there is a airlock the bottom rad hose will remain soft and cool while only the top hose is firm and warm.
Happened to me. The rad coolant system needed a big burp.

 

I ran it until it warmed up top hose is hot bottom is only warm and I also noticed the top half of the radiator is very hot and bottom is only warm.What is the best way to burp coolant system?

Thanks for your help

 

I slowly poured coolant down the rad cap hole while the ATV was idling with the front end up slightly higher (4") on blocks or ramps. Have some one shake/rock the ATV by the handle bars as you pour into the rad.
It just did a spit/burp out of the rad hole and was fine ever since.

Just looking down the rad hole I could tell the coolant was flowing better and the bottom rad hose was firm and warm.
You may want to get that thermostat back in also. I checked mine in a hot pot on the stove and it was opening and closing OK.

Good luck.

 

mine was overheating because of a bad/leaking head gasket. she still ran well when cold, but started to spit white smoke/steam out the muffler when warm, and antifreeze would spit out of the overflow bottle. did a whole top end and shes great now.