Brand new here and I did search - but not finding the exact same problem. So here goes (and thanks in advance for any input!):

I have replaced the recalled ECM, changed the oil and had the radiator cleaned & flushed on my 2005 Sportsman 700 Twin. The fan works fine and the bike starts & runs very nicely. HOWEVER... the "ENGINE HOT" light flashes after riding for a little bit (5-10 mins). This happens especially when I have it open a bit (4500-5000 rpms), but will even do it when I am running 3500-4000.

What has me really stumped is that when I opened the front cargo area and the radiator cap cover to let it vent better, I noticed no heat. So I (carefully) moved my hand to the radiator cap itself and was able to lean on the thing! It was barely even warm!! This is very frustrating!

I am not a mechanic at all, but don't mind trying simpler ideas myself. Can anyone help?

 

It sounds like you might have air in the system. If I recall, you'll need to take off the radiator cap, jack up the front end of the ATV a little and let it run till the fan cycles a few times, topping off the coolant each time. Or at least i think that is how it is for most Polaris ATV's. Im sure someone more helpful (OPT) will be along shortly.

 

Do what Cummins Driver recommended,plus make sure the area behind the radiator is free from dirt and mud. I've found these caked over the years especially around the fan area.May take awhile to purge all the air from the system so leave the radiator cap off. You can squeeze the hoses to help in purging,plus both hoses should feel firm afterwards. Make sure you don't have any coolant seepage around the water pump weep hole or any wet areas behind the radiator.Even a small pin hole leak can cause problems.If coolant doesn't appear to be circulating and it still runs hot after purging for awhile,you may have to pull the water pump cover to check that the impeller nut hasn't backed off or for any damage to the w/p impeller vanes from heat and cavitation.

 

Thank you both for the quick replies - it sounds like removing the cap and listening for the fan to cycle is something even I can do! I will try that today, checking the list of items mentioned by OPT. Fingers crossed.

 

Check the sending unit. Mine read hot even tho it was good

 

Well, a couple weeks later and I was finally able to get the ole 700 out for a shakedown. I followed the steps outlined and was able to add fluid 3 or 4 times, so I think there was air in there.

The odd thing is now the machine seems to run clean as long as I am moving, but the very moment I pull up, it starts flashing hot again. I ran about 40 minutes the other day and it was cool (pun intended) but I pulled off for a quick stop and it immediately started flashing. Same thing a few times...different speeds, different time frames, but each time I stopped, it would flash. If I throw it back in gear and take off, it stops. ugh.

Initially, I'd think it's just being air-cooled, but could the temperature really change that much the very SECOND I stop the machine?

 

A few things I'd still check.The thermistor sensor(on the cylinder) can be checked as to whether it decreases ohms resistance as it heats up.Measure at room temp and drop in boiling water then test.Resistance should drop. The ecm module controls the charging to the battery and also kicks on the fan as it's major function.Even though you replaced it, make sure the battery is receiving at least 14 volts while at an idle. The system has to have 12 volts constant for the module and also for the fan to kick on properly. Fan motors can get weak after a period of years also and take more amperage to kick on,(takes a meter set on dc amps hooked to the fan wiring,when the fan kicks on if it takes more than 15 amps,the fan motor could be suspect) If a battery cell has shorted out,it may not be able to hold a charge and cause problems. You can have it load tested.