Another over heater..

I have a 2007 500 HO X2
The last 2 years i have had it overheat a few times.. very sporadic..
Last year i changed the rad fluid, I always clean out the rad.. everything looks good.
Yesterday i was up a logging road, and all of a sudden i could feel serious heat coming out of the engine, and then bam it just shut off. No warning light or anything.
Fan was running.. has full fluid..
Keeps tunring over.. i let it sit for about 10 mins, and then it ran fine for the day?

maybe the fan isnt coming on soon enough?
What could be the problem do you think.. like i say its very intermittent.