CB500s Overheating

[Dark-Strom]

Posting for a friend (Help Kwackboy) 
If let idling too long the temp gauge shoots from far left to about 3/4 on the gauge, at which point it pisses itself from the header tank?
There is a voltage supply to the cooling fan switch on the rad, however the fan doesn't operate.
I understand the temp gauge is on the thermostat housing.
Is it best to just take out thermostat or replace the fan switch or fan unit?
Thanks.
 

[tallpaul]

Take off the fan switch and put a meter across the terminals. Put it in some boiling water and see if it switches. If it does switch then suspect the thermostat. If it doesn't then the switch is duff. This is how I would test it.

Edit: also consider that if the switch does close then it may also be a duff fan...

[kwackboy]

Hello ,

CB500's are basic and very reliable so if you have any cooling issues there's very little to check.

The things that go wrong are , a seized thermostat, fan switch, stuck fan and a blown fan fuse.

Being an old bike I'd first check the coolant by removing the tank and then the coolant cap from the thermostat housing , it's probably low.
Then check the fan is free from dirt / stones, check it's fuse, then turn on the ignition and bypass the fan switch by simply earthing out the wire that plugs into the fan switch on the radiator, you can do this by touching the wire to any good earth point on the frame, doing this will hopefully operate the fan.

Fans can go wrong but it's rare.

By taking the fan switch out if the equation and checking the coolant level you are checking the basics. 

By the symptoms you describe though it's sounds to me the thermostat is stuck, it's always good to remove it and see what happens without it.


Check the above first and then get back to me , if it's the fan switch I will tell you how to check it .

Edit.....

tallpaul has just described how to do it .. 
 

[Dark-Strom]

Thank you both very much,

I should have added that I previously (pre-lock down) checked the fan fuse (10 Amp red) and this was OK.
The bike has done about 25k.
I know the coolant was flushed / replaced about 18 months ago when it had a full service etc.
Sounds like the shorting the fan to earth will be a good elimination step, there is only 1 wire (12v supply).
If the fan works, will try checking the switch - then pull off the thermostat housing etc...

Will get back to you once free to play.

I did try and find a thermostat on-line, some £45 with delivery from Italy?