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I'll suggest that the Gen 1 & Gen 2 fan switches are 2 different sizes of threads into the radiator, so NO!
 

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I did this mod to keep the idle temp closer to running temp, before it'd creep up to 220F.
Kicks on at 197F off at 188F
Temp at 30mph: 172F avg
Measured at thermobob, ambient temp 95F
 

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Discussion Starter · #29 · (Edited)
For those asking after the Gen 1 and Gen 3 equivalent parts, this will help.

The Gen 1 switch is a skinny thing that completes a circuit to ground. It is a thermal switch. When that circuit is completed the fan relay is activated and the fan turns on. It is mounted in the bottom tank of the radiator. It has an M10X1.25 thread. It looks like this:
Auto part Fashion accessory Metal Electronics accessory Engineering

The Gen 2 is a short, fat switch that completes a power circuit, just as a flip switch would. It is a thermal switch. It handles the power directly with no relay. It is mounted in the bottom tank of the radiator. It has an M16X1.5 thread. It looks like this:
Plumbing fitting Cylinder Metal Household hardware Fashion accessory

This is the Gen 3 water temperature sensor. It is not a switch, it is a sensor that delivers a variable voltage signal to the ECU. The ECU decides when the fan comes on by energizing the fan relay. It is mounted in the top of the cylinder head. It has a British Pipe Thread that is almost the same size as a 1/16"NPT. It is the BSPP straight (not tapered) thread type and the sensor seals against the head on an o-ring.

It is not the same as the Gen 2 water temperature sensor, it just uses the same hole in the cylinder head.

It looks like this:
Cylinder Auto part Plumbing fitting Metal Audio equipment

All of the OEM switches are expensive - ~$60. All of these devices have generic aftermarket equivalents that are inexpensive - ~$15.
 
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I bought a cheap Chinese made switch from Amazon for my Gen 1. It looked just like the switch it was supposed to replace, but when I went to thread it into the radiator I found out the threads did not match up. The radiator on my KLR is bright aluminum and appears to be an aftermarket unit, so now I'm at a loss. I need to find out what brand it is in order to get a new fan switch, but I don't see a name on it.
 

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For those asking after the Gen 1 and Gen 3 equivalent parts, this will help.

The Gen 1 switch is a skinny thing that completes a circuit to ground. It is a thermal switch. When that circuit is completed the fan relay is activated and the fan turns on. It is mounted in the bottom tank of the radiator. It has an M10X1.25 thread. It looks like this:
View attachment 35012
The Gen 2 is a short, fat switch that completes a power circuit, just as a flip switch would. It is a thermal switch. It handles the power directly with no relay. It is mounted in the bottom tank of the radiator. It has an M16X1.5 thread. It looks like this:
View attachment 35018
This is the Gen 3 water temperature sensor. It is not a switch, it is a sensor that delivers a variable voltage signal to the ECU. The ECU decides when the fan comes on by energizing the fan relay. It is mounted in the top of the cylinder head. It has a British Pipe Thread that is almost the same size as a 1/16"NPT. It is the BSPP straight (not tapered) thread type and the sensor seals against the head on an o-ring.

It is not the same as the Gen 2 water temperature sensor, it just uses the same hole in the cylinder head.

It looks like this:
View attachment 35017
All of the OEM switches are expensive - ~$60. All of these devices have generic aftermarket equivalents that are inexpensive - ~$15.

Tom do you know if the sensor has different temp options like the radiator sensors?
 

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Discussion Starter · #32 ·
I doubt it, @daave. A sensor like that, designed for coolant, should be built to send in the range of something like -30*C to +120*C with a linearly varying voltage output from 10mV to 100mV*. That's not to say that there aren't similar sensors that are calibrated differently in terms of *C vs voltage. You might be able to find one that is in the same body, but the specs aren't readily shared on these devices because there's no reason to; they exist in the parts catalogs at the OEM level so that engineers can pick and choose, but those values don't find their way into user manuals or shop manuals.

If there was a reason to spoof the sensor output to make the ECU do something different it should be pretty easy to do, though. You'd just need a voltage divider to drop the voltage or an additive voltage circuit to increase the voltage. And you'd probably need to be able to measure voltage in at least the millivolt range, if not microvolt.

And to be clear, the radiator switches are not sensors. They are switches. The switches are operated by bi-metallic strips that are set to close the contacts at one temperature and open them at another. A sensor is a device that always gives out a signal, but it varies in accordance to the magnitude of some physical attribute, such as temperature, pressure, light, sound, etc.

*I made all those numbers up, but you get the idea. The water temperature sensor needs to send a signal of varying *C vs voltage across the expected operating range to tell the ECU what the temperature associated with some action is.
 

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I doubt it, @daave. A sensor like that, designed for coolant, should be built to send in the range of something like -30*C to +120*C with a linearly varying voltage output from 10mV to 100mV*. That's not to say that there aren't similar sensors that are calibrated differently in terms of *C vs voltage. You might be able to find one that is in the same body, but the specs aren't readily shared on these devices because there's no reason to; they exist in the parts catalogs at the OEM level so that engineers can pick and choose, but those values don't find their way into user manuals or shop manuals.

If there was a reason to spoof the sensor output to make the ECU do something different it should be pretty easy to do, though. You'd just need a voltage divider to drop the voltage or an additive voltage circuit to increase the voltage. And you'd probably need to be able to measure voltage in at least the millivolt range, if not microvolt.

And to be clear, the radiator switches are not sensors. They are switches. The switches are operated by bi-metallic strips that are set to close the contacts at one temperature and open them at another. A sensor is a device that always gives out a signal, but it varies in accordance to the magnitude of some physical attribute, such as temperature, pressure, light, sound, etc.

*I made all those numbers up, but you get the idea. The water temperature sensor needs to send a signal of varying *C vs voltage across the expected operating range to tell the ECU what the temperature associated with some action is.
Sounds like it would almost be easier to just install a fan switch for hot days.
 

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Discussion Starter · #34 ·
The KLR is not going to overheat. It never has. I have ridden at supra-legal speeds in Death Valley at 115*F and crawled along dirt roads shortly thereafter. It won't overheat. I was overheated, but the bike was fine. Let the cooling system do its job, just do the usual due diligence and make sure that the system is full of coolant, including the reservoir and that the nipple hasn't melted off of the reservoir. See below, this IS a known issue for the KLR and might oughta be attended to. I expect it is still a potential issue on the Gen 3.

The KLR's cooling system has always been more than adequate, but folks just don't like to see anything but a dead-center needle. If it isn't solidly in the red, it's not too hot.

Trust us on that one.
 

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Discussion Starter · #36 ·
About 260*F.
 

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Discussion Starter · #38 ·
Yes, it applies to your 2006.
 

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Yeah, I didn't install this switch because I was concerned of it overheating, I just wanted to keep the bike in a more consistent temp range, and it will probably only ever be needed while idling. I actually wish the bike ran about 10F hotter normally
 

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Yeah, I didn't install this switch because I was concerned of it overheating, I just wanted to keep the bike in a more consistent temp range, and it will probably only ever be needed while idling. I actually wish the bike ran about 10F hotter normally
q.v., Post # 34 above.

If you'd prefer running a hotter (than stock) nominal operating temperature, a Thermo-Bob, with its higher (than stock) temperature thermostat, might fulfill your objective. As to, "consistent," temperature range, don't know of any damage caused by stock coolant temperature excursion (within manufacturer's design limits). Regardless, Thermo-Bob stabilizes coolant temperature, beyond stock cooling system's capability.
 
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