I have a Kawasaki ZX636 which is over heating...

Temp gage is not working, will work for a minute where it will go to 80c then jump down to 40c then will disappear. the comes and goes...

I can smell the coolant overheat from the radiator but there is no smoke coming out anywhere.
I have just rode it into work and have done no trouble shooting as yet. but it does not look like the Fan turns on at Idle and cannot tell if it turns on when moving.

Any help would be greatly appreciated as I have to ride home today and it is going to reach 40c