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1994 Klr 30000 miles I installed the thermo-bob and my fan doesn't turn on. The fan runs when I touch the wire to the engine fin. It warms up to about 1/2 way on the gauge and the fan doesn't turn on. Am I being to impatient. I can say not sure the fan was working before I installed the thermo-bob part of why I probably thought I needed it. I uninstall the thermostat and tested it and it opens properly I did buy a new switch and installed it also. Not sure how to proceed. Any ideas. I'm not much of a mechanic but this seemed pretty simple. Thanks in advance
 

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Procedure for testing thermal switch in service manual (your wife WILL let you use here kitchen range, right?).

:)
 

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It is not supposed to turn on until the needle hits the red mark on the gauge.
 
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It is not supposed to turn on until the needle hits the red mark on the gauge.
True! If the temperature gauge needle stays out of the far-right red zone (Generation 1, anyway), you don't need to activate no stinkin' radiator fan!

On Generation 1s, an operational thermal switch in the lower radiator closes at a coolant temperature in that region of around 200 degrees F. (if I remember correctly). This closure of the thermal switch contacts connects a hot wire from the fan relay to ground, closing the relay's contacts and sending power to the fan motor. Don't think Generation 2s have fan relays; instead, direct full fan motor power is routed to the thermal switch. (No speaka much Generation 2; corrections welcomed!)

For those using temperature gauge degree overlays: The temperature gauge measures coolant temperature near the cylinder head, typically higher than coolant temperature at the bottom of the radiator.
 

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It is not supposed to turn on until the needle hits the red mark on the gauge.
What Tom said; sounds like everything is operating as designed.


Dave
Well it is not very often that I disagree with either Tom or Dave to much degree, but I will on this.

IME, most KLR fan switches will turn on by at least 3/4 of scale, my Gen 1 turns on at 5/8 scale. And as long as it stays below the RED Zone, all is well.

With the Thermo-Bob installed my Gen 1 the gauge normally hovers between 7/16 & 9/16 of temp scale on the open road & the fan is NOT running. Just as it is supposed to operate.

To the OP,
I think that you were overly impatient.
 
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Paul,

Instead of being lazy and just agreeing with Tom, I should have said that half way on the gauge doesn't turn on the fan on either of my KLR's and that the fan not coming on at 1/2 way is normal. He's tested the fan switch and everything seems to be functioning as I would expect. I suspect he's chasing a non-existant problem. Better?

Dave
 

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Discussion Starter #8
Thanks everybody I have never paid any attention to when it comes on. Thought i might be being a little in patient. Since everything else seemed correct. Had this bike quite a while and tires and oil about all ever done ( yes have the doo and a thermobob) and what started this whole mes was breaking the subframe in march. Thanks again
 

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Well it is not very often that I disagree with either Tom or Dave to much degree, but I will on this.

IME, most KLR fan switches will turn on by at least 3/4 of scale, my Gen 1 turns on at 5/8 scale. And as long as it stays below the RED Zone, all is well.

With the Thermo-Bob installed my Gen 1 the gauge normally hovers between 7/16 & 9/16 of temp scale on the open road & the fan is NOT running. Just as it is supposed to operate.

To the OP,
I think that you were overly impatient.
Indeed, the radiator fan on my Gen II sans T-bob activates at about 3/4 of the temperature scale, well ahead of the needle aligning with the red area.

Jason
 

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Gauge, no 2 indicate the same I have found.

I particularly liked my Ducati 851S temp gauge. About the time it dropped a cylinder to help with cooling, the temp needle would be almost in the red. On the 916 the fans kicked in when the gauge was almost 1/2 way and were as loud as the dry clutch!!!!
 

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My advice for what its worth. Start the bike and let it sit there and idle. if the needle hits the red and it doesn't come on then yes its probably malfunctioning.
 

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If the fan proves still not to work after you let the bike heat right up check the earth wire which runs from the fan securing bolt to frame is ok. The radiator is rubber mounted and without this the circuit will not complete.

Sent from my moto g(8) plus using Tapatalk
 

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If the fan proves still not to work after you let the bike heat right up check the earth wire which runs from the fan securing bolt to frame is ok. The radiator is rubber mounted and without this the circuit will not complete.
I think the thermal switch in the lower radiator somehow connects with a ground (earth) to activate the fan, awayonmybike. The ground (earth) within the coolant in the lower radiator connects the hot wire from the fan relay (Generation 1) or fan motor (Generation 2), completing the fan motor circuit, through the thermal switch; connection completed when the coolant in that volume exceeds around 200 degrees F. (q.v., "Fan System" wiring diagram, Electrical System, Clymer.)
 

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The feed wires that supply +12v and Ground to the fan also carry that ground to a lug terminal. This is affixed by the lower fan mounting bolt and supplies the ground to the fan switch.
* When the temp exceeds ~205dF then the fan switch closes and
* This provides the ground to the fan relay circuit.
* That causes the relay contacts to close and
* This allows the +12v to be fed to the fan, causing it to spin.

 

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The feed wires that supply +12v and Ground to the fan also carry that ground to a lug terminal. This is affixed by the lower fan mounting bolt and supplies the ground to the fan switch.
Certainly the fan motor needs a ground connection to operate (as shown in the B/Y wire in the diagram below):



However, I think (or thought) the ground connection for the thermal switch was through its threads connected to the radiator (didn't think/know the radiator was electrically isolated from the frame, as awayonmybike posts above).

This picture shows a single wire to the thermal switch; continuous + 12 VDC on my Generation 1 in my experience:



I've been unaware of a separate ground connection (other than thread contact with the radiator) for the thermal switch.

Appreciate the insight provided!
 

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Yeah, the thermal switch has to ground to the metal of the radiator and then the metals are grounded to the harness, chassis & battery by the Black/Yellow wire. The fan motor does have its own separate ground wire.

If a rubber mounted radiator is not mechanically ground via a wire to the chassis or electrical harness the internal electrolysis will quickly cause pin-hole leakages to develop.
 

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Yeah, the thermal switch has to ground to the metal of the radiator and then the metals are grounded to the harness, chassis & battery by the Black/Yellow wire. The fan motor does have its own separate ground wire.

If a rubber mounted radiator is not mechanically ground via a wire to the chassis or electrical harness the internal electrolysis will quickly cause pin-hole leakages to develop.
Yep, let me fix the image to reflect the tie-in where the Radiator ground splits off from the motor and runs down to the fan mounting bolt.'

... fixed! :smile2:
 

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If a rubber mounted radiator is not mechanically ground via a wire to the chassis or electrical harness the internal electrolysis will quickly cause pin-hole leakages to develop.
Hmm, steel is more noble than aluminum, so if steel and aluminum are connected and immersed in a solution the aluminum will sacrifice itself (corrode) to the steel. Essentially, the aluminum becomes a sacrificial anode. But if an aluminum vessel, such as a radiator is isolated from steel and the aluminum is exposed to a solution, the corrosion rate of the aluminum should be minimal.

Perhaps I don't understand what you're saying here.

Jason
 

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Well, with the fan switch connected there and to the +12v electrical system it's not really isolated.

The ground wire from the fan connector allows the fan switch to complete the circuit for the fan relay.
 
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