CBF500 overheating… cooling system fail


How it all started

Some time ago my bike started to overheat badly. I realized just in time to prevent engine damage. After further investigation I have found out that the fan stopped working.  I decided to take the bike to the garage. Mechanic established fan is not broken and there is coolant in the system.  He suspected that the “ground” has been lost due to the corrosion between connecting surfaces. It was a likely scenario however could not be fixed while I wait. Theyt did a workaround for me instead.  They attached a piece of wire to the well grounded bolt and enabled me to connect the fan directly when I wanted.

An attempt to fix

Thinking that the diagnosis is correct I got prepared an one sunny day I got the tools out. I removed the coolant (had to remove the  seat and the fuel tank to gain access to the top cap). I disconnected the fan, disconnected the radiator and removed it from the bike (fan is screwed to the radiator). Than I cleaned all the components, removed the rust, repainted the fan cover to prevent corrosion,  cleaned all the connection points to the bare metal and than fitted it all back together and onto the bike… Then I refilled the cooling system fitted the tank, seat etc… THIS DIDNOTSOLVE THE ISSUE… The fan still would not kick in when expected…


I sat down with Haynes manual and found that the thing that the fan connects to (screwed into the radiator) is the heat switch.  It is supposed to make the connection when the water reaches the right temperature.  This seemed to be the broken part as I was sure now that the fan connections are grounded as good as they could be. I ordered the part and waited for another sunny weekend to do the job.

In the meanwhile – more trouble

Some other things needed fixing on the bike while I waited for the switch … There were engine mounts/spacers that looked badly corroded. I wanted to replace them for a while.  I had the parts but when tried to take the engine mounting bolt the bolt would not move for nothing… in the meantime the old mounts literally fell apart as I loosened the screw… I did not feel it was ok to ride for long distances of any sort… and I could not fix it myself… So I took it to the local garage… They did it couple days later and charged me ?260 as they could not get it out with heat and had to cut and drill it out.

The day the steam rised…

The situation above was the day I picked up the bike… I saw that the temperature started to raise and wanted to switch the fan on using my “workaround”… it turned out the mechanic found it unnecessary and cut it off… Why has he not spoken to me beforehand I cannot comprehend. To make it even better he did not tighten the coolant top cap properly after working on the bike (they had to remove the radiator to get access to the bolt). As the temperature raised the water started boiling out through the cap and onto the engine creating the steam you see in the video…  Obviously once the coolant level went down the effectiveness of the cooling was further deteriorated…  I got home but – This was not a good day

What happened when I got home?

The switch arrived on a previous day and I suspected the lose cap issue. I confirmed it just after I got the tank off. I was pissed off! After disconnecting the radiator I replaced the switch and re-filled the system.  I started the bike and waited for the engine to heat up. THE FAN KICKED IN! it was such a beautiful view 🙂


This was a very bad experience however I have learned quite a lot from it. Now I know probably most of what I should know about the cooling system on the cbf500 🙂 The pump is the only mystery but I hope I will not need to learn about it in near future.

mine was leaking as the cap was not on properly. Fan was not starting due to a failed sensor. First of all check your fluid level and if the cap is locked.