Question: Does a switch like the thermostatic one in the radiator degrade and fail due to time, or use?

Reason for inquiry: Fan was working at the end of last season. After starting the bike for the first time this spring (took half an hour) I changed the oil and coolant. With the bike up to temp I noticed the fan does not come on anymore, even at the upper limits of the gauge.

I grounded the switch and the fan spins; so I know it gets good voltage, the fuse is good, and the fan motor is fine.

This leads me to suspect the switch (or am I missing something?).

And hence my question, is it common for the switch go bad while just sitting over the winter.

 

not too sure about it being "common", but they do fail. as i'm sure you know, as the switch heats up it completes the ground side of the circuit via the radiator. since grounding the wire makes the fan come on, the fault must be in the grounding of the switch. to work the switch must:
1. get hot and internally make the circuit. it must be touching coolant, not air.
2. have a good connection to the radiator. the threads must be clean
3. radiator must be grounded to the frame. there should be a wire somewhere.

fortunately, fan switches are a cheap fix and easily installed. its not a bad idea to replace it anyway.

 

Assuming you grounded the connector at the switch when the fan turned on and didn't tap into the wire elsewhere it has to be the switch or radiator ground as 74demon suggested. If you tapped into the wire past the switch there is also the possibility of a bad connection to the switch terminal also.

If you have a multimeter check for continuity to ground somewhere on the metal housing of the switch. If there is good continuity the switch is likely failed.