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1984 GL1200 Aspencade - I notice the radiator fan doesn't come on no matter how much I ride the bike. Tested the fan with a battery and it works. The thermostat fuse is okay, so I'm guessing it might be the thermostat switch (part# 37760MB9000)? #11 in the diagram below

Just wondering if the fan not working could not be the thermostat switch? Could it be the thermostat? (part# 19300MG9000) #1 in the diagram below

My understanding is the thermostat switch allows current to flow to the radiator fan motor once the coolant reaches a certain temperature?

What is the thermostat (#1 in the diagram below) measuring the temperature of?

323365
 

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The 'thermostat' (item 1) is a mechanical valve that allows the water to circulate in the cooling system ( no effect on fan start/stop, other than keeping the engine cooled when it opens around 180 to 190 F).

The SW.,THERMOSTAT (item 11) is what turns the fan on/off. You stated you don't have it coming on while riding, that can be very true, due to the air flowing across the radiator. The sure way to get it to come on (I've found) is to ride it for a ways and then stop riding and let it idle for a while. You should see the temperature gauge climb and the fan will start (if the switch is working), just don't let the temperature climb into the 'red zone'. The switch should close when the coolant reaches 208 - 216 F. If you want to check the circuit short across the switch terminals and the fan should run.

I presume you have checked the 10amp fuse 1 to make sure you're electrified? Does your brake light work? If not then you have a ground problem.

Good luck
 

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Does the gauge go up (hot enough) for the fan to turn on?. Usually about 3/4 way up. Does the gauge work properly with no erratic movements? The easiest way to check the wiring for the fan circuit is use your test light. One end in one wire terminal and the other end in the other terminal. With the key on the light should light up if all is good.
 

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Discussion Starter #4
The 'thermostat' (item 1) is a mechanical valve that allows the water to circulate in the cooling system ( no effect on fan start/stop, other than keeping the engine cooled when it opens around 180 to 190 F).

The SW.,THERMOSTAT (item 11) is what turns the fan on/off. You stated you don't have it coming on while riding, that can be very true, due to the air flowing across the radiator. The sure way to get it to come on (I've found) is to ride it for a ways and then stop riding and let it idle for a while. You should see the temperature gauge climb and the fan will start (if the switch is working), just don't let the temperature climb into the 'red zone'. The switch should close when the coolant reaches 208 - 216 F. If you want to check the circuit short across the switch terminals and the fan should run.

I presume you have checked the 10amp fuse 1 to make sure you're electrified? Does your brake light work? If not then you have a ground problem.

Good luck
There seems to be a lot of people who replace the thermostat switch. I will try what you recommended first.
Is the thermostat a pretty reliable part or is it prone to failure like the thermostat switch?
 

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There seems to be a lot of people who replace the thermostat switch. I will try what you recommended first.
Is the thermostat a pretty reliable part or is it prone to failure like the thermostat switch?
Original thermostats almost never fail.
 
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The switch can develop a layer of goo that somehow causes it to be less sensitive. Taking the switch out, however is a fairly involved job, but it can be cleaned.
Many try to replace the switch with something aftermarket. That is a bad idea. They have different parameters and can open too soon and have the fan running almost constantly. Plus the plugs are not the same, so by modifying yours, it becomes less reliable.
You don't say where you live, or the riding conditions. There's a chance the fan isn't coming on because it doesn't need to. Here in the Phoenix area, my fan usually doesn't come on unless I'm in stop and go traffic.
 
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