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2007 Polaris Trail Boss 330 Overheating

Zachary Coombs

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Hello, I’m new to this forum, I have a 2007 trail boss 330 that’s been overheating after about 5 minutes of riding. No problems before it overheats from a cold start but then it backfires and loses power. The fan comes on but the temp light doesn’t. I’ve had someone clean the carburetor, I’ve replaced the spark plug and air filter and put in a new battery. I also tried cleaning the radiator with a hose, Any help is appreciated, Thanks

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Welcome to Quadcrazy, sounds like your thermostat is ether partially opening or not opening at all.  Or your water pump is on its way out.  When the fan comes on does  it spin normal (fast) ? If so then number one the sensor is brining it on properly and two the fans spinning at a good rpm, leaves only the thermostat or the water pump as the problem. Both are inexpensive and I would change them both at the same time  since the coolant has to be drained to replace either one   

It wouldn’t have anything to do with the carburetor or battery etc.  


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Sorry I forgot to mention it’s air cooled, so it’s not really a radiator it’s a oil cooler theres no water pump. The thermistor switch seems to already be jumped to the solenoid, don’t know if that’s from the factory since I bought it used. The oil cooler gets really hot after a few minutes, the fan does run very fast. Does this make a difference?? Thanks again


Edited by Zachary Coombs
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I looked it up and yes it’s an oil cooler and  the thermister that bring the fan in. 

The temp light comes on when the engine gets super hot.  Have you checked that oil cooler for cleanliness? If the fan is spinning at a good rpm and the coil is clean then it could be a poor oil pump performance.  

Also is the engine painted ? That can cause additional heat build up that can trigger this type of thing.  


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I haven’t taken it off but I’ve power washed it and used and a hose to try to get any mud out, I can see through it for the most part. The engine isn’t painted. The guy I bought the quad from said it has less than 8 hours riding time and he let it sit for about 10 years. Everything was fine for the first 10 rides after I bought it, I decided to change the oil and oil filter, the air filter and the spark plug and that’s when it started giving me problems. Since then I’ve cleaned the carburetor, bought a new battery, and the carb boot had tear in it so I replaced that. The fan never came on once it started overheating, The thermistor was connected to the top of the solenoid which I found had no voltage so I connected it to the bottom that’s powered straight to the battery, the weird part is the starter is still connected to the top and works fine?. At first it seemed like a lean condition with it backfiring but now it’s just running way too hot and loses power/backfires. Any ideas?

Edited by Zachary Coombs
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Lean condition would be from the air fuel mixture screw being set wrong or from a dirty carburetor etc.   

A hot spark plug is a plug that produces a bigger spark (hotter) spark.   

Pull the spark plug and look at the color. If it’s a light brown/tan color then that’s good. Black not good, post a pic of the plug. 


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