Why is my fan running?

[easternrider]

Out on my bike ride the other day, temp below 60F, I am sitting at a light for less than a minute, and my fan comes on!!! WTF!!! I said, as It seemed too cool outside for it to need to run. May I be having coolant flow issues, maybe thermostat?

On top of this, when the fan did come on, my volt meter on the dash went from 14 volt down to 12 or a little less, and sounded/felt like it was going to stall, Again WTF?

[Snaggletooth]

First question would be where is your temp gauge reading at during this? From my experience if the coolant is expremely low you may not get a high reading on the guage as there may be more air in the thermocoupler than coolant. Check the level at the oveflow bottle.

 

With a high reading it could be low coolant, sticky thermo, or failing waterpump.

 

If you suspect the thermostat itself being stuck shut try this.

 

Change the coolant drain valve from the normal run position (OFF at 2 o'clock) which makes the coolant move through the thermostat to the drain position (ON at 2 o'clock) which bypasses the thermostat but still allows full flow through the system.

 

You may see a drop on the temp gauge if the thermo is not opening.

 

Worst case..... your's is an '84 which if never changed the impeller in the waterpump is plastic. Some have shown signs of deterioration. If the pump has ever been replaced it will be a metal impeller.

 

Way to check the pump for flow..... back to the drain valve.

 

With the bike cooled off and coolant level topped off, and the drain valve in the (ON) position......remove the radiator cap. You're gonna lose some coolant during this so be ready for that.

 

Start the bike and idle. (Don't snap the throttle with the cap off). As you look into the radiator you will see the coolant moving. As you increase the RPM's the flow will increase and even throw coolant out of the top. If your's in moving at a good rate the impeller is working fine.

 

Move the drain valve back to the (OFF) position and you will see the flow stop, at least until the thermo opens. Replace the cap and check overflow bottle level.

 

 

As far as the voltage dropping, well yeah. The radiator fan motor draws a lot of amps. As well I would guess you may be stopped and the brake lights on, another major drain with the two 1157's fired up in the back.

 

So there's a couple of things to look into for now. Let us know what you find.

 

 

This pic is the valve set to (OFF) for the noraml running position.

Edited June 29, 2013 by Snaggletooth

[easternrider]

So there's a couple of things to look into for now. Let us know what you find.

This pic is the valve set to (OFF) for the noraml running position.

 

 

Well, I really didn't find anything. Did as you said, cap off, start bike....coolant was moving, and more as I throttled up. Checked thermo. and from what I could tell it was working also. Level in tank was good, etc......

Maybe this is normal, but I do not remember it running this much before.

Anyway, thanks for the input.

[Flyinfool]

My fan will kick in often if doing a lot of stop and go city driving, even at 50 degrees.

My fan comes on just before the temp gauge gets to the red and will shut off at around 2/3rds on the gauge. If its over 100 it does the same thing.