Motorcycle Repair: overheating, thermostat temperature, radiator cap

Question
I have a 96 cbr f3 600 that is running super hot. After inspecting it I found a bad return hose ( the small hose from the impeller to the case) and replaced it. I thought this would solve it but it didn't. Then I noticed that the fan was not coming on so i checked it and bypassed it and got it running. Now with the fan running and all hoses good it still over heats in a matter of minutes. I did notice that there seems to be no pressure at all in any of the hoses when i squeeze them. Am I right in assuming that the impeller is bad. As for the fan not running on its own is this because no water is running thru the radiator and tripping the sensor? Any help would be greatly appreciated. Thank you

Answer
Hi George,

Do you have the service manual? If so, test the temp sensor/fan switch and thermostat per manual's instructions.

Impellers rarely go bad.

I suspect air is in the cooling system and causing the problems.

Check out this link for more intel:

http://faq.f650.com/FAQs/Overheating_FAQ.htm

Respectfully,
Mark Shively



Coolant Overheating & Servicing
By Mark Shively

Motorcycle and ATV cooling systems are air-free by design. Air in the cooling system lowers the boiling point of coolant to just above the point of which water boils and causes engine overheating.

Air enters the cooling system anytime the system is opened by changing the coolant, replacing the thermostat, temperature sensor, fan switch, or when other repairs requires draining coolant.

It is important to purge air from the system after servicing. The exceptions to this are opening the radiator cap or coolant reservoir cap for routine inspection and periodic maintenance.

The Mityvac Company manufactures a tool for purging air from cooling systems. The tool is the AirEvac tool. The Mityvac Cooling System AirEvac Kit refills cooling systems in minutes without trapping air that can cause overheating. The kit combines a universal adapter with a compressed-air-operated Venturi vacuum to quickly eliminate trapped air by purging and refilling the cooling system under vacuum.

The result is an air-free cooling system. Higher coolant boiling temperatures ensures a cool running engine and optimum performance.