When I first start my trail boss the overheat light comes on. I know it can't be overheating when you first start it. I saw on posts that other peoples overheat light comes on and the fan runs. Only my light comes on and my fan does not. I disconnected the thermistor plug while the atv is running and the fan comes on with the light still on. I did not want to take the chance of riding it because if it does overheat the fan my not in gauge. One more thing...I have never heard the oil cooler fan start up. Anybody have any info that may help?

 

Thermistor module sounds like it's shorted out. You can check ebay, Cycle Parts Warehouse, Partzilla,etc on replacement. Most people never hear the fans come on unless super hot. Never had fans kick on when they came in for service unless they idled in a hot area for extended periods.

 

:crazy Since the fan never comes on that I have noticed, is it safe to drive? Will this take care of the light being on? I heard you mention a ect sensor and a ecm. Can one of those be the problem and where are they located? I have a universal manual that is worthless. It does not show anything related to my 2002 polaris 325 trail boss. Also can that thermistor be cleaned out? Thanks OPT

 

You can download a service manual here for a small fee.

 

Don't worry safe to drive.. Just the module showing a false hot light. You don't have an ecm on this model. Just replace the module and hopefully all will be ok.. Rare instances I've seen that the Thermistor senor on the oil cooler neexed to be replaced also but doesn't sound like your case. Having to use my phone, internet's down or link to the best prices.. 4 inch screen,6 inch wide fingers.. Plus look in the manual. Fan doesn't kick on until about 220 degrees or so on these oil cooled models to begin with..

 

Man that thing is expensive! Cheapest I've found on the thermistor module is $305.Polaris 4010590 - SWITCH-THERMISTER,LR-62 : Dealer Cost Parts Never defeated one,but might be worthwhile to see if you can and just toggle the fan connector from any brown (ground) and red/white wire(only powered up with key on) and use it when slow moving for extended periods and under loads. A lot of oil and air cooled machines out there running around that don't even have fans.Plus according to the manual the fan kicks on at 260 degrees,kicks off at 240 degrees and the hot light kicks on at 290 degrees! Most won't ever see these kind of temps.

 

Hi OPT. Wow $305 for a part....that is not going to happen. What is the thermistor part coming off the oil cooler. That is what I unconnected and reconnected. It's black and about 2 inches long. That part is about $90 and doable. Could it be a bad connection coming off the $305 thermister. Maybe it needs to be cleaned at the connection, kinda like a battery? If not a toggle switch would work for me.

 

The thermistor sensor is on the oil cooler. Its main job is to close its contacts if it gets hot enough and supplies the ground path for the fan to kick on. Like I mentioned fans rarely kicked on unless super hot. The hot light problem is usually from the high $ module located on the firewall,not usually the oil cooler sensor. Nothing that I know of to be able to service this thing since it's sealed.It's "Possible" to disconnect the thermistor module from the harness I guess,block off the oil cooler thermistor sensor with a same size bolt. Then run a ground wire to the fan brown wire and tap into a red white harness wire interrupted by a toggle switch to go to the fan hot wire.That way you can turn the fan on and off when needed. I might be thinking out loud here,haven't done this before myself,but sounds logical as Spock would say..

 

It looks like the toggle switch it is. OPT thanks for all your help on this atv problem!

 

Just thinking also that you don't have to pull the thermistor from the oil cooler and block it off,just leave it in and zip tie the connector to the oil cooler mount if you're going to toggle the fan.