I have an 09 model, owned for nearly three years.  At my last trial it started kicking out black smoke and misfiring when revved.  It was suggested that the temperature sensor sometimes fails and causes this.  That the fan would subsequently come on from stone cold seemed to confirm this diagnosis. 

I have just fitted a new sensor but the fan still comes on from cold and, after ten minutes running in the garage, is not switching off. I have not had a chance to ride the bike but clearly a cure has not been achieved, though such revving as I have been able to give it shows no black smoke. There is no sign of physical damage to wiring etc to have caused a short circuit to keep the fan running.

Has anyone experienced this and able to offer a possible solution?  There's plenty coolant in the system.

This may not be relevant but when I first got the bike the fan seemed to be on a lot of the time; I think this is just a 4RT characteristic, though I had thought the fan was not coming on so frequently in recent months but there was no sign of overheating so I put it down to my imagination.

Edited February 22, 20188 yr by 2stroke4stroke

On the 4RT, the coolant temperature sensor sends data to the ECU. The ECU uses temperature data for fuel adjustments and to start the fan by signalling the fan relay.

So the next thing to check is the fan relay. See the schematic in your owners manual, and Page 6-9 shows how to check the fan relay.

mine ran with black smoke, turned out to be the ecu...see if you can borrow one to try

Thanks guys - problem solved.   Corrosion in the connector to the relay.  The only connector I did not clean and grease when I got the bike as I didn't know it was there.