I would do a coolant flush. First drain out the old, fill it with distilled water, fire it up and let it run for about five minutes. Then drain out the water, and refill with coolant, you can buy the regular coolant, and mix it yourself at a 50/50 mixture of coolant and water, but i like to use the pre-mixed stuff, and it is only about 2 dollars more, and one gallon will be enough. You could also have a bad thermostat, but i would think if it was bad or stuck it would overheat in just a couple minutes. Does your engine light come on? If the bike is overheating your light should come on. Also if you have never changed your anti-freeze since you bought it i would buy some prestone radiator cleaner, it comes in a yellow bottle, all you do is fill the radiator with distilled water, and add the bottle of cleaner, and if i recall start the engine and let it run for 15 minutes, and then drain and refill, this will clean out the radiator of any sludge, or clogs i used this stuff in a dirt bike of mine that was overheating and the amount of crap that came out was amazing. after you refill the bike with fresh antifreeze you will have to start it let it run a couple of minutes, and the add some more antifreeze, after you fill it lean the bike from side to side to help get out any air bubbles after you fill it the first time YOU WILL HAVE TO ADD MORE! Just keep leaning it from side to side, and then start it, let it run and then top it off.

 

Good point about adding distilled water. Unless you know that you have soft water it is cheap insurance to use "store bought water".
What type of riding do you do? slow city, interstate,ect? Do you have to add coolant periodically? How long between oil changes and what weight oil? Do you sometimes smell coolant from your engine?
I read that if you go a step farther and buy deionized water to mix with your undiluted antifreeze it has the same effect as engine ice.
Our bikes have aluminum engines and will they not take a lot of extra heat before things go bad wrong.

 

No radiator on a C90... they are air-cooled.

 

air cooled

They are a mix of air/oil cooled. Anyone have experience with this?

 

They are a mix of air/oil cooled. Anyone have experience with this?

I had my 2006 C90 for 4 years, and yes it would get hot down here in the deep south during summertime... especially at stop lights and in heavy traffic... but that is the nature of a air-cooled engine. The ignition's proximity to the engine can make it get hot as well as the key. Not sure if yours is running hotter than "normal" - how long have you had the bike? Have you noticed a change in running temp now versus previous summers? Have all the recalls for your bike been performed?

If you go to a full synthetic oil versus dino, it should lower the engine temp somewhat. What oil are you running now (type and viscosity)? Change your oil regularly? Ensure the level is always at the full mark?

Have you installed a hi-flow air filter, but not changed your air / fuel ratio with an add-on fuel management system? If so, that could be the cause of the bike running hot and the sputtering as well (both caused by running an extremely lean a/f ratio)... this is about all I can come up with... maybe someone else can add some additional things to check.

 

I'll take a WAG (wild azz quess).

'05 C90's were known for stators going bad. Going bad from heat. Is it possible an impending stator failure could be generating the heat and other problems you describe?

 

Also, SWAG. Scientific wild azz guess.

We always said those came from the "smart" side of the hangar.:biglaugh: