Radiator FAN Not Coming On

DominoEffect said:

I check edmy fuse. It’s good, I checked the fan by grounding it, it works.

I let the bike idle for a while, never kicks on. I’m wondering if the switch is bad. Anyway to test that switch without removing and letting all the fluid drain out.

However, I do live in Seattle and it might be too cool still to over heat while idling.

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My VT1100C2 ACE runs its fan fairly often. On the other hand, my VT600C only cycled it's fan on 3 occasions in the the two years I was riding it, and two of these were after I re-jetted leaner. Since I tested every component on both bike's systems, I'd conclude that how much the cooling fan turns on might be quite variable depending on specific model and state of tune of the machine.

But, I think it's wise to have an operating cooling fan, and personally I think it's wiser, more efficient, and will give longest service life, if one runs the engine in the sweet spot, temperature wise, (neither too cool, nor too hot) which requires a working and calibrated fan switch.

The test does require removing the switch, but you can catch your fluid in a pan and reuse it, if it's fresh. If it's not fresh, you should be replacing your coolant every few years anyway, since the anti-corrosion chemicals get weak over time. Here's the procedure:



The same basic procedure, a pot of hot coolant on a heat source, and a thermometer, is used for testing the thermostat.

The thermosensor, that lights the overtemp indicator light, on the other hand, is designed to operate at a temperature above boiling, so to test that component requires a fluid with a higher boiling point than coolant, or a pressurized chamber. But that device and circuit is almost totally uneccessary, in my opinion. If you know your fan is working correctly, you can gauge your system temperature by noticing the fan cycling.

torinogt said:

Agreed, I live in Southeast Louisiana, & the only time my fan would come on is when riding low speed/stop & go in the dead heat of Summer.

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When you think about how much air is moving past the radiator traveling at any normal road speed, vs. how much air the fan is capable of moving, it seems obvious why the fan gets to take a lot of time off.

On giving this system a little more thought, I'm thinking that the fan switch and fan are not as important as I suggested. If the fan is on constantly, the system will thermocycle on the thermostat. This is how our cars would work way back when cars had fan belts and ran off the crankshaft, before somebody invented the thermal clutch. The fan would just run all the time. When you are traveling, the contribution of the fan to the cooling air flow is negligible. When you are stopped, the fan may cycle.

Seems to me that the most important component in the cooling system, besides the water, is the pressure cap. Changing liquid water to steam consumes lots of heat energy. It takes 540 times more heat to boil a gram of water, than is does to raise the temperature of that water by 1 degree C. If you shut down promptly when boilover occurs, this natural phenomenon should protect your engine. As long as there is water in the jacket, the temperature can't get higher than boiling.

It's been a long time since hopper cooling systems were used on vehicles, but this very simple system is still in use on utility diesel engines like the Changfa. This has no radiator, it just boils off water to stay cool.





I vaguely remember limping my old Buick V8 home, with an open radiator cap and a jug of water under the hood to makeup for boilover.