Mine did that last year. Turned out to be a bolt had come loose and dropped down to block the fan from turning. I got caught in traffic and it smoked a little - got home and it made a mess. Topped up the coolant (not realizing the fan problem), next day I hit heavier traffic and ended up with a cloud of white smoke, a pissed off rider, and a tow to the dealer who promptly found the problem and charged me next to nothing to fix it.
I'd check your fan is not blocked.