Not to insult your intelligence, but how do you know it's overheating? Is the gauge showing is as being too hot? Is the fan running continually or for very long periods of time, especially when you're riding it or after you shut it off? When it's hot, do you smell hot antifreeze wafting around the bike? Does coolant bubble out onto the ground when it's hot? Have you recently had the coolant changed?
I know that's a lot of questions to ask, but I guess I want to know if the bike is actually overheating, is the gauge faulty or does it just seem or feel hot to you.
First off, if you recently had the coolant changed, there could be an air pocket in the radiator. The radiator is designed to be completely full and if there's air in there, they'll run hot. The system needs to be "burped" and since all bikes are different, you need to ask your dealer or someone with your model bike on how to do that.
Have you washed your bike with a high pressure car wash wand? If so, the super high pressure water can bend the radiator fins over, reducing air flow through it. Tale a look at it and it will be obvious if the fins are bent and not letting air through. They make "combs" that will straighten the fins but you should probably let a radiator man do that. If just some of the fins are bent, you can use the end of a clothes pin and carefully straighten the fins yourself.
There is a thermostat that works like the furnace or air conditioner thermostat on the wall in your house. It's meant to regulate the coolant temperature. They sometimes go bad and can make an engine either run too hot or too cool.
The radiator is also designed to run under pressure, which raises the boiling point of the coolant. The radiator cap regulates this pressure and while not common, sometimes they fail and won't hold enough pressure.
While rare, sometimes the sensor that tells the gauge what to do go bad and send faulty signals. There are ways of testing the sensor to see if it's functioning properly but you'll need a manual, multi meter and a little bit of electrical knowledge.
If you think it's running hot because the fan runs a lot or all the time, again a sensor could be bad. A bad sensor could also not turn the fan on soon enough. My experience has shown that if the fan is still running even after you've been moving at a decent speed for some time or if it runs and runs and runs after shutting the bike off, then it is too hot. Usually the fan will run for just a bit after you've shut down, but not for 5 minutes or more or keep cycling on and off.
I've tried to list things in order of possibility. Then there's always the very rare things like water pump impellers that are loose on the shaft, leaking head gaskets and so on but as I said, that's extremely rare. Good luck.
