Okay, so my Dad has a 2003 Trailblazer 400 and it has been an insanely reliable, bulletproof wheeler. Last year, while on a ride, the fan didn't come on and it starting spraying boiling coolant out of the little pin hole in the top of the red cap on the reservoir. He took it to a local shop and they determined that the radiator cap was bad. They replaced it and its been fine since. Well, that is until this past weekend. My wife was riding it around our property when it did the same thing (no fan and spraying coolant). I don't want my dad paying $350 for a radiator cap again so I started digging into it. If I unplug the sensor in the lower left of the radiator, the fan does NOT come on. If i wire the fan directly to 12v, it comes right on and runs perfect. I cleaned all of the connections and still nothing. My question is, should I replace the sensor or could the radiator cap really be bad again, after only 1 year? The radiator is clean and so is the fan, wheeler runs great and the charging system is working as it should. Also, is there a part number for the cap and sensor for local parts stores? (NAPA, Autozone, etc...) Thanks in advance!!

 

$350 for a cap?? wow!!
gonna have to test the sensor

 

The cap was around $20, the $330 or so was BS labor charges. How do I test the sensor??

 

13 psi radiator cap at any auto supply for around 8 bucks or less. You can get one on ebay that crosses over to the part#4010161.Cooling Engine Thermal Switch Sensor Fits Polaris 4010161 | eBay Or you can get Wells SW526 at any auto supply,cut the connector end off and use your old one. Think I'd find another dealer also.. Test the ohms resistance on the sensor leads when cold. Drop it in hot water and resistance levels should drop. If they don't the sensor is bad.

 

Thank you so much! One more question, how to I bleed the air from the system after I get it all back together?

 

Easier to purge trapped air on the 400 2 stroke than the 4 strokes. Engine off! Leave the radiator cap off,loosen the 10mm bleed bolt on the head(located close to the temp sensor on the back of the head) and let all the air bubbles pass until you have straight coolant flowing out, then close the bolt. Top off the radiator and over flow bottle.

 

So, I should do all of that with the engine off??

 

Yes,engine off..