Took delivery of a heavily 'modified' CB500 from Fast Bikes Mag a few weeks ago and have just finished sorting it out today, it had been sat around doing nothing for a couple of years.
I found it was overheating in traffic - and the fan wasn't kicking in. First suspect was a faulty fan or fan switch. However shorting the wire between the fan and the fan switch to ground produced sparks and span the fan up - so the fan worked OK....
So then it seemed the sensor on the radiator might be at fault, harder to test without draining the system etc, but it still might be the thermostat not letting coolant get to the fan switch. So taking the tank off allowed me to get at the thermostat, which I took out and boiled up in a saucepan of water, it opened fine. So water was able to circulate but I wasn't sure it actually was. So I ran the engine up with the radiator cap off allowing any air to escape and sure enough it did - I was then able to add more coolant. Despite the coolant level looking fine, it seemed there may not have been enough in there, the coolant I could see inside the radiator neck must have been held there artificially.
So it turned out there was an airlock in the coolant system somewhere, meaning coolant wasn't circulating and hence not getting the fan switch hot enough to turn the fan on, making the situation worse. Having topped up the coolant, I put everything back together and took it out for a spin, the temperature was much more stable and, when I got back and left it ticking over to see what would happen, sure enough the cooling fan now kicked in as it should.
Problem solved! Hope useful for someone else...
I found it was overheating in traffic - and the fan wasn't kicking in. First suspect was a faulty fan or fan switch. However shorting the wire between the fan and the fan switch to ground produced sparks and span the fan up - so the fan worked OK....
So then it seemed the sensor on the radiator might be at fault, harder to test without draining the system etc, but it still might be the thermostat not letting coolant get to the fan switch. So taking the tank off allowed me to get at the thermostat, which I took out and boiled up in a saucepan of water, it opened fine. So water was able to circulate but I wasn't sure it actually was. So I ran the engine up with the radiator cap off allowing any air to escape and sure enough it did - I was then able to add more coolant. Despite the coolant level looking fine, it seemed there may not have been enough in there, the coolant I could see inside the radiator neck must have been held there artificially.
So it turned out there was an airlock in the coolant system somewhere, meaning coolant wasn't circulating and hence not getting the fan switch hot enough to turn the fan on, making the situation worse. Having topped up the coolant, I put everything back together and took it out for a spin, the temperature was much more stable and, when I got back and left it ticking over to see what would happen, sure enough the cooling fan now kicked in as it should.
Problem solved! Hope useful for someone else...
