Motorcycle Repair: 99 YZ400F Cooling Problem?, yamaha yz400f, coolant level

Question
Hi Falcon,

I just bought a 99 Yamaha YZ400F.  Got it home day before yesterday and everything seemed ok.  I did notice a fluid overflow after riding approx 15min.  The over flow was from the front black drain tube.  I thought it was from the gas tank, but the fluid looked greenish and smelled sweet not like gas.  Today I cranked it and left it to idle with the choke on, to warm it up before riding.  When I return a few minutes later the bike was smoking bad from the front not out the pipe.  I shut it down and noticed a wet spot under the black drain tube and also possibly some oil drops on bottom of frame up front.  I thought I had blown it big time.  After it cooled down I checked the radiator(?) or at least what looks like a radiator and it seemed LOW or empty.  As my situation and question probably shows, I don't know much about mechanics.  Is this really bad or something that I can fix?  Any help or suggestions would be greatly appreciated.  I hope I did'nt just buy a lemon!?!  I was able to crank the bike after it completely cooled down. I did immediately turn it back off.  I did'nt want to over heat it if that is what is happening.
Thanks,
Ward (New Rider)

Answer
Hi Ward.
 The greenish liquid is coolant.  You could have a problem with the water pump or the cooling fan.

A problem with the cooling fan could be either a bad fan motor, a bad Thermosensor or a short in the wiring to the fan motor system.

There is also the possibility of a bad thermostat preventing the coolant from flowing.  Get the repair manual and check your coolant level and perform all possible tests listed therein on the fan/thermosensor wiring and cooling system components.

If there is nothing wrong with any of those, then there is the possibility of something in the cooling system that is blocking the coolant flow.

Start with those and let me know what you find.
Good luck.
FALCON