Force fan to stay on or add a switch?

SniperX · 1 Force fan to stay on or add a switch? Sat Mar 18, 2017 2:51 am

SniperX

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My 85 K100RT has been running fantastic since the timing chain I did and everything else last summer. How do I force radiator fan to either stay on, or where to splice a switch in to make it come on when I wish it to? Right now it isn't coming on at all. Possibly a fuse?

charlie99 · 2 Re: Force fan to stay on or add a switch? Sat Mar 18, 2017 4:49 am

charlie99

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indeed add a switch

for me its a test device ,,,if I'm heading out into the hills ...and the fan doesn't work ..I aint going nowhere

not the fact that I probably wont need it , whilst travelling , its the unpredictability about holdups behind traffic on return etc

its pretty easy to do

the "efi trouble shooting" link in the portal page documents the terminals and usage for the temperature relay (which turns on the fan when required )

don't forget the sensor on the water stub is the signalling device to that relay

you can test the connections to the temperature sensor, by measuring the pins 10 and 13 at the under seat computer (efi computer )..also documented in the same thread
Force fan to stay on or add a switch? Test-FI%201

Force fan to stay on or add a switch? Test-FI%201

but make sure the fan rotates easily to start with , before exploring other options

you can take a switch wire and ground it through a switch ...then the other end of the switch should connect to the pin "e" of the temp relay
which will make it think that it is in an over temperature situation ..and thus turn the fan on ...at will

Force fan to stay on or add a switch? Fan%20circuit

Force fan to stay on or add a switch? Fan%20circuit

of course this only works whilst the engine is running

good luck

SniperX · 3 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 2:32 am

SniperX

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Number of posts : 171

charlie99 wrote:indeed add a switch

for me its a test device ,,,if I'm heading out into the hills ...and the fan doesn't work ..I aint going nowhere

not the fact that I probably wont need it , whilst travelling , its the unpredictability about holdups behind traffic on return etc

its pretty easy to do

the "efi trouble shooting" link in the portal page documents the terminals and usage for the temperature relay (which turns on the fan when required )

don't forget the sensor on the water stub is the signalling device to that relay

you can test the connections to the temperature sensor, by measuring the pins 10 and 13 at the under seat computer (efi computer )..also documented in the same thread

but make sure the fan rotates easily to start with , before exploring other options

you can take a switch wire and ground it through a switch ...then the other end of the switch should connect to the pin "e" of the temp relay
which will make it think that it is in an over temperature situation ..and thus turn the fan on ...at will

of course this only works whilst the engine is running

good luck

Brilliant! Cheers! And many thanks for the response! As soon as I get back from Phoenix, I'll do the mod with a switch. Oh, is there a specific after market fan that works better than stock and at least semi directly replaces the standard bit?

Laitch · 4 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 2:55 am

Laitch

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SniperX wrote:

Oh, is there a specific after market fan that works better than stock and at least semi directly replaces the standard bit?

Yes!

Last edited by Laitch on Sun Mar 19, 2017 9:44 am; edited 1 time in total

SniperX · 5 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 2:56 am

SniperX

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Number of posts : 171

Laitch wrote:

SniperX wrote:

Oh, is there a specific after market fan that works better than stock and at least semi directly replaces the standard bit?

Yes!

Thanks! Now can you point me in the right direction for it?

Laitch · 6 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 2:58 am

Laitch

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Already have. Smile

SniperX · 7 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 3:17 am

SniperX

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Laitch wrote:Already have.

AH HA! Thanks again!

charlie99 · 8 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 3:44 am

charlie99

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if your going in to the fan assembly ..best advice I can give is to clean the blades as a first option

crud builds up on the leading edge and actually all over the blades ..thus decreasing airflow greatly ...call it cavitation if you will , but if you clean it up you will see a huge difference in flow

its a bugga to do ..but no where near hard

don't forget to lubricate the brass bushings whilst your in there ....wd40 is not a suitable lubricant ...however it will loosen up seized crap ready for a good lubricant

just a heads up

good luck

Holister · 9 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 4:31 am

Holister

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AFAIK there are 2 thermisters in the sensor which signals both the FICU and the Temp Relay. To properly test the temp sensor with respect to how it's connected to the temp relay you need to measure resistance between Temp Relay pins #E(sensor) and #31(earth). Testing at the FICU plug will only measure the thermister and wiring for the FICU. It will however give you an indication of the condition of the common earthing which is thru the sensor body to the engine block. Cheers
Force fan to stay on or add a switch? Relay-tray

Force fan to stay on or add a switch? Relay-tray

KiwiK100 · 10 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 4:44 am

KiwiK100

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Absolutely right Charlie, and not to forget giving the radiator a good bath in hot water to loosen all there crud that builds up between the fins. Once soaked a good firm tap on the garage floor will knock out a surprising amount of debris. Be careful using compressed air as the fins are VERY soft and will fold and collapse if too much air pressure is used too close to the fins.
Water temp will run noticeably cooler when the radiator and fan blades are clean.

Dai · 11 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 8:57 am

Dai

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KiwiK100 wrote:Be careful using compressed air as the fins are VERY soft and will fold and collapse if too much air pressure is used too close to the fins.

Don't use a powerhose either. DAMHIK.

SniperX · 12 Re: Force fan to stay on or add a switch? Sun Mar 19, 2017 3:14 pm

SniperX

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KiwiK100 wrote:Absolutely right Charlie, and not to forget giving the radiator a good bath in hot water to loosen all there crud that builds up between the fins. Once soaked a good firm tap on the garage floor will knock out a surprising amount of debris. Be careful using compressed air as the fins are VERY soft and will fold and collapse if too much air pressure is used too close to the fins.
Water temp will run noticeably cooler when the radiator and fan blades are clean.

Good thing I did that when I had it all apart last whilst doing the timing chain, and everything else! Thanks for the advise though!

SniperX · 13 Giving it a go tomorrow... Sun Apr 09, 2017 1:23 pm

SniperX

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I'm getting a chance to give it a go tomorrow or Wednesday. I have been busy on a different project for a bit. A mate gave me a 1977 Plymouth Trailduster with 52K miles original on it so I have been busy doing my Re-start after two years of sitting on it. Hopefully the re-start will be successful today and I'll go from there.

Peterk100rs · 14 add a switch. Sun Apr 09, 2017 1:40 pm

Peterk100rs

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So I added a switch to my k100rs last week . Fan wasn't coming on and when I tested the cabling it was faulty . Basically I followed the cable from the fan to up under the tank, its close to the front on left side. Its here where it connects to the wiring loom. I cut the connector off and ran a cable up to a switch which I installed on the switch rail where the key is and just ran it to the battery .
The fan worked instantly. So i basically only turn it on when I come into town where there is generally a lot of sitting about in traffic.

SniperX · 15 Re: Force fan to stay on or add a switch? Sun Apr 09, 2017 9:36 pm

SniperX

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Peterk100rs wrote:So I added a switch to my k100rs last week . Fan wasn't coming on and when I tested the cabling it was faulty . Basically I followed the cable from the fan to up under the tank, its close to the front on left side. Its here where it connects to the wiring loom. I cut the connector off and ran a cable up to a switch which I installed on the switch rail where the key is and just ran it to the battery .
The fan worked instantly. So i basically only turn it on when I come into town where there is generally a lot of sitting about in traffic.

Good to know, I'll do that is I can't find the fault in mine which I should be able to do.

Holister · 16 Re: Force fan to stay on or add a switch? Sun Apr 09, 2017 10:10 pm

Holister

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Peterk100rs wrote:So I added a switch to my k100rs last week . Fan wasn't coming on and when I tested the cabling it was faulty . Basically I followed the cable from the fan to up under the tank, its close to the front on left side. Its here where it connects to the wiring loom. I cut the connector off and ran a cable up to a switch which I installed on the switch rail where the key is and just ran it to the battery .
The fan worked instantly. So i basically only turn it on when I come into town where there is generally a lot of sitting about in traffic.

While removing the Temp Controller from the equation won't affect the performance of the engine, it does mean that you've removed an element of safety and reliability. I think your bike has a temperature gauge?? If not, probably a good idea to install one so you can keep an eye on it. Better to get the fan/temp controller to work as it should imo.

Hopefully you've run the power to the switch and not to the fan itself, but more importantly, it's not a good idea to pick up the power directly from the battery as you've done, for two reasons.

Your fan is running off un-switched 12V. This means that when you turn the ignition off, you will still have power to the fan switch. If you forget to turn the fan off after you've parked, you're battery will not only run down but it will possibly be ruined.
Your fan is now unfused. This means that if the fan melts down which they can do, or you have a wiring short, you run the risk of an electrical fire which has the potential to damage other wiring or even you whole machine. I'm pretty sure the temp controller is fused on #6 (7.5amp). The fan itself is fused via the temp controller (jumps off the horn relay) thru fuse #7 (15amp). This is where I'd be picking up the power for the fan switch.

Point-Seven-five · 17 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 12:07 am

Point-Seven-five

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I don't think you want to run the fan all the time. These engines are designed to run at a specific temperature controlled by the thermostat. In conditions were the engine is running in a cold environment the fan will prevent proper warm up or at best delay the rise to operating temperature, leading to accelerated wear.

Best to run the fan off the thermo switch with the manual switch only for those times you are stuck in traffic in hot weather.

Peterk100rs · 18 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 6:54 am

Peterk100rs

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Holister wrote:

Peterk100rs wrote:So I added a switch to my k100rs last week . Fan wasn't coming on and when I tested the cabling it was faulty . Basically I followed the cable from the fan to up under the tank, its close to the front on left side. Its here where it connects to the wiring loom. I cut the connector off and ran a cable up to a switch which I installed on the switch rail where the key is and just ran it to the battery .
The fan worked instantly. So i basically only turn it on when I come into town where there is generally a lot of sitting about in traffic.

While removing the Temp Controller from the equation won't affect the performance of the engine, it does mean that you've removed an element of safety and reliability. I think your bike has a temperature gauge?? If not, probably a good idea to install one so you can keep an eye on it. Better to get the fan/temp controller to work as it should imo.

Hopefully you've run the power to the switch and not to the fan itself, but more importantly, it's not a good idea to pick up the power directly from the battery as you've done, for two reasons.

Your fan is running off un-switched 12V. This means that when you turn the ignition off, you will still have power to the fan switch. If you forget to turn the fan off after you've parked, you're battery will not only run down but it will possibly be ruined.
Your fan is now unfused. This means that if the fan melts down which they can do, or you have a wiring short, you run the risk of an electrical fire which has the potential to damage other wiring or even you whole machine. I'm pretty sure the temp controller is fused on #6 (7.5amp). The fan itself is fused via the temp controller (jumps off the horn relay) thru fuse #7 (15amp). This is where I'd be picking up the power for the fan switch.

Fan is wired through a fuse which i installed in the fuse box in a spare slot and linked through power to the light Relay so It cant be turned on unless bike is started. The switch has a led so I can visibly see it on and yes the bike is fitted with a temp gauge.
Basically I didn't want to pull apart the wiring loom incase I created any more issues as I have been down this road before.
So far this has worked fine with no issues. Changing the temp sensor made no difference as the issue was in the wiring loom.
However I had originally intended just to fit a new temp sensor which I did but no use no fan and water was boiling over .

Crazy Frog · 19 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 7:34 am

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There is no need to pull new wires(except for the LED and the switch) or install a new fuse. The switch should be connected to the ground and carry no power. Positive for the light/LED can be the one for the parking light.
Have you tried a simple testing of the temp relay?
When grounding (earthing) pin E, you should get +12V at pin A2. If this doesn't work, I would say that the temp relay is bad.
This is the proper installation without butchering the original wiring.

Force fan to stay on or add a switch? Temper10

Peterk100rs · 20 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 8:39 am

Peterk100rs

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Crazy Frog wrote:There is no need to pull new wires(except for the LED and the switch) or install a new fuse. The switch should be connected to the ground and carry no power. Positive for the light/LED can be the one for the parking light.
Have you tried a simple testing of the temp relay?
When grounding (earthing) pin E, you should get +12V at pin A2. If this doesn't work, I would say that the temp relay is bad.
This is the proper installation without butchering the original wiring.

Good info there , I will try that .Thanks

BobT · 21 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 10:49 am

BobT

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I ride in all weather and am not worried at all about the fan. I could install a switch for the summer but then the engine might not get as hot as BMW designed it to. I know that if I fitted a switch then I would also look to improve that system by making the fan come on automatically, then I realised that it does that anyway.
Has anyone blown a cooling system on a K100 because the fan did not work and the engine got too hot?

92KK 84WW Olaf · 22 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 11:01 am

92KK 84WW Olaf

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BobT wrote:I ride in all weather and am not worried at all about the fan. I could install a switch for the summer but then the engine might not get as hot as BMW designed it to. I know that if I fitted a switch then I would also look to improve that system by making the fan come on automatically, then I realised that it does that anyway.
Has anyone blown a cooling system on a K100 because the fan did not work and the engine got too hot?

Came close to it on the LT.!

Easily done this part of the world where its not so hot that you leave the K at home.

Which is why my RT got a nice work over in February with a full clean out and a new fan which comes on regularly. Cooling system all ok, pump replaced three years ago and no airlocks. Just the traffic where I travel the last part of my trip to work.

BobT · 23 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 11:55 am

BobT

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92KK 84WW Olaf wrote:

BobT wrote:I ride in all weather and am not worried at all about the fan. I could install a switch for the summer but then the engine might not get as hot as BMW designed it to. I know that if I fitted a switch then I would also look to improve that system by making the fan come on automatically, then I realised that it does that anyway.
Has anyone blown a cooling system on a K100 because the fan did not work and the engine got too hot?

Came close to it on the LT.!

Easily done this part of the world where its not so hot that you leave the K at home.

Which is why my RT got a nice work over in February with a full clean out and a new fan which comes on regularly. Cooling system all ok, pump replaced three years ago and no airlocks. Just the traffic where I travel the last part of my trip to work.

Olaf, are you saying that you never did any damage due to overheating? Come close is not a scientific measurement it either over heated and blew the cooling system or it didn't.
Engines run at their most efficient when hot, and a high oil temperature is most important, but no one on a bike knows what the oil temperature is as they only fit water temperature gauges to bikes.

92KK 84WW Olaf · 24 Re: Force fan to stay on or add a switch? Mon Apr 10, 2017 12:12 pm

92KK 84WW Olaf

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Boiled it over.......in heavy traffic in winter. And in Perigueux in the urban part fan was running full time on the RT while moving in your nice 35C weather. Wonder how that would have been with no fan running....

Hot is indeed efficient but once the fan is on it means the engine has reached its maximum capacity to get rid of the excess heat, unless you can improve it by moving/moving faster. No fan and you reach that limit in a very short time. Park bike and go for a cool beer at that point.

SniperX · 25 It's FAN TIME! Mon Apr 17, 2017 4:25 pm

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Removed enough of the fairing to find out the fan is partially seized so I will have to replace it. It is hard enough to turn by finger, that I feel as if it need about 10lbs of pressure on the blade to make it move. I feel it's gacked and ready for the bin.

SniperX · 26 Laitch, have a question... Mon Apr 17, 2017 4:29 pm

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Laitch wrote:Already have.

Have you personally done this swap? If so, (or not!) do you have to just install the fan with the custom bracket (which I can easily make) and plug it in like the stock one?

Has anyone tried the SPAL unit? Looks like a good fan from online reviews on other vehicles and oil coolers which is what I found most.

Point-Seven-five · 27 Re: Force fan to stay on or add a switch? Mon Apr 17, 2017 7:17 pm

Point-Seven-five

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I have installed the Spal fan in my K100RS. It's an easy job once you have the radiator out.

No need to make a new mount. The old one can be used after the crap Bosch fan is removed.

You simply remove the tabs on the Spal fan so it can slide into the original mount. A cut in the original mount allows it to open up to fit that Spal fan into it, and you then pop rivet the Spal into the original mount.

The Spal fan is about 1mm larger in diameter than the Bosch, so it is not a bad fit once the mount is cut. The only other work that needs to be done is to ovalize one of the mounting holes to line up with the radiator.

Whole job takes about an hour once the old fan is out of the bike.

Here's the description I followed:

http://www.motobrick.com/index.php/topic,4313.msg26399.html#msg26399

Go to reply #18 dated December 20, 2014.

Flip2 · 28 Re: Force fan to stay on or add a switch? Fri May 19, 2017 10:02 pm

Flip2

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Where is a good area to locate this override switch and led for the fan ?and what kind of switch( simple toggle) or maybe something I've seen on motobins perhaps? in the future I might install a temperature gauge as well .
86 k100 rs

duck · 29 Re: Force fan to stay on or add a switch? Sat May 20, 2017 2:57 pm

duck

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Spal fan:

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/fans/fans.htm

Holister · 30 Re: Force fan to stay on or add a switch? Sun May 21, 2017 7:11 am

Holister

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Flip2 wrote:Where is a good area to locate this override switch and led for the fan ?and what kind of switch( simple toggle) or maybe something I've seen on motobins perhaps? in the future I might install a temperature gauge as well .
86 k100 rs

Usually the dash on the handlebars has one or two spare slots for an additional switch. A toggle switch is all you'll need. You could try buying a second hand switch to fit the dash from Motorworks/Motobins. You'll need to run a wire from the temp controller up thru the steering head and to the dash plus another earth wire back to the main earth point under the tank.

Temperature gauge runs off a different temp sensor which screws into the drain plug on the water pump.

Flip2 · 31 Re: Force fan to stay on or add a switch? Sun May 21, 2017 2:26 pm

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Peterk100rs wrote:

Crazy Frog wrote:There is no need to pull new wires(except for the LED and the switch) or install a new fuse. The switch should be connected to the ground and carry no power. Positive for the light/LED can be the one for the parking light.
Have you tried a simple testing of the temp relay?
When grounding (earthing) pin E, you should get +12V at pin A2. If this doesn't work, I would say that the temp relay is bad.
This is the proper installation without butchering the original wiring.

Good info there , I will try that .Thanks

Crazy Frog , at first I thought I understood your diagram but could you explain it for a beginner?

Flip2 · 32 Re: Force fan to stay on or add a switch? Sun May 21, 2017 6:23 pm

Flip2

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Tracing the wiring from 45(on the temp relay-15 in diagram)appears to go to 86 pin on the horn relay and not to 30 of load shed as the diagram states. . . Thanks for all the prev info group.

SniperX · 33 Which of the two fan wires is hot Fri May 26, 2017 1:07 am

SniperX

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I'm replacing my fan in the next couple days. With the SPAL fan. Need to know which wire is hot and which is earth on the stock fan colour wise so I can wire up the new fan polarity correct.

duck · 34 Re: Force fan to stay on or add a switch? Fri May 26, 2017 2:55 am

duck

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Violet/yellow is 12V
Brown is ground.

SniperX · 35 Re: Force fan to stay on or add a switch? Fri May 26, 2017 3:05 pm

SniperX

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duck wrote:Violet/yellow is 12V
Brown is ground.

Thanks much Duck Cheers!

SniperX · 36 Re: Force fan to stay on or add a switch? Mon Jul 03, 2017 12:58 am

SniperX

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Got the fan on the rad finally. Been working so much on the ranch I just finally got the time to do it this weekend. It'll be back on the road tomorrow. Ended up doing the SPAL fan, and fitting it to the original housing after removing the stock fan. Old fan cut from housing,
Force fan to stay on or add a switch? 19657079_1435166906576465_6036884659267984444_n

Force fan to stay on or add a switch? 19657079_1435166906576465_6036884659267984444_n

Housing sans old fan
Force fan to stay on or add a switch? 19598437_1435166959909793_1800965506443444433_n

Close up of SPAL tabs that I removed with a sander and cutoff tool
Force fan to stay on or add a switch? 19601280_1435166989909790_7243562689227999162_n

Force fan to stay on or add a switch? 19601280_1435166989909790_7243562689227999162_n

SPALL rivited into stock housing
Force fan to stay on or add a switch? 19601304_1435167063243116_8784162038010033296_n

Completed fan in housing
Force fan to stay on or add a switch? 19657033_1435167133243109_5870547713025978263_n

Back in situ!
Force fan to stay on or add a switch? 19554830_1435167476576408_7946298631287887682_n

duck · 37 Re: Force fan to stay on or add a switch? Mon Jul 03, 2017 1:07 am

duck

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Nice job!

Flip2 · 38 Re: Force fan to stay on or add a switch? Mon Jul 03, 2017 8:35 am

Flip2

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I tried that method and it would not fit on my 86k100rs , . I was pissed spent s bunch of time grinding etc and it was still catching at the sides near the top . I ended up using a couple pieces of aluminum stock ( as suggested elsewhere ) and that was a pita as well . the spal fan is nice but the Bosch motor replacement would have been a piece of cake .

SniperX · 39 Re: Force fan to stay on or add a switch? Mon Jul 03, 2017 2:47 pm

SniperX

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Flip2 wrote:I tried that method and it would not fit on my 86k100rs , . I was pissed spent s bunch of time grinding etc and it was still catching at the sides near the top . I ended up using a couple pieces of aluminum stock ( as suggested elsewhere ) and that was a pita as well . the spal fan is nice but the Bosch motor replacement would have been a piece of cake .

You probably didn't cut the stock mount for the SPAL to fit in. Yes it was a bit fiddly, but all in all I am happy with the results because the entire thing feels more sturdy than the stock fan. And with the SPAL in situ the fan is actually closer to the rad because the blades and SPAL housing is right at the edge of the stock mount. But there is still plenty of clearance between the rad and the housing.

Flip2 · 40 Re: Force fan to stay on or add a switch? Mon Jul 03, 2017 8:18 pm

Flip2

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Glad yours worked mate .No I did exactly what you did , cut the original mount , riveted it together and had it on the radiator before attempting to install it several times along with removing/grinding more of the original mount , bummer .

SniperX · 41 Re: Force fan to stay on or add a switch? Tue Jul 04, 2017 12:44 am

SniperX

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Flip2 wrote:Glad yours worked mate .No I did exactly what you did , cut the original mount , riveted it together and had it on the radiator before attempting to install it several times along with removing/grinding more of the original mount , bummer .

Was it because the top mount with the rubber grommet was off centre a tad? Mine was and I massaged that as well. I simply rounded out the hole for the needed spot for the grommet to gon back in, and the metal spacers to go back in and the 5mill socket went right back in,.

SniperX · 42 Re: Force fan to stay on or add a switch? Tue Jul 04, 2017 12:45 am

SniperX

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duck wrote:Nice job!

Thanks Mate! And for your help as well!

Cheers!

Kev

SniperX · 43 Re: Force fan to stay on or add a switch? Tue Jul 11, 2017 1:57 am

SniperX

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So, if I understand this correctly... The mod to add a switch to the fan to force it into the on position grounds the fan correct? So there is a hot provided constantly whilst the bike is running, and the relay gets a signal from the temperature sensor, then the relay connects the ground to the fan in order for it to come on...so if I just tap into the ground wire on the fan itself, and switch it to ground from a single pole single throw switch it will come on? Is it that simple?

robmack · 44 Re: Force fan to stay on or add a switch? Tue Jul 11, 2017 7:57 am

robmack

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The mod that forces the fan on with a switch never touches any of the circuitry that powers the fan. So, your explanation and conclusions above are incorrect. The modification runs a switched lead to ground that parallels the water temperature sensor in the stand pipe. With the switch open, everything works normally. With the switch closed, the temperature sensor is short-circuited to ground. This simulates the same conditions as a very overheated engine, and tells the temperature relay it should turn on the fan to cool the engine; so the fan starts up.

SniperX · 45 Re: Force fan to stay on or add a switch? Tue Jul 11, 2017 4:05 pm

SniperX

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Great! Which wire on the sensor is the ground? Thanks.

robmack · 46 Re: Force fan to stay on or add a switch? Tue Jul 11, 2017 6:29 pm

robmack

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You won't find a ground wire on the sensor. The body of the sensor is the common connection. The body is screwed into the stand pipe which is bolted to the engine which itself is bolted to the frame which is electrically connected to the battery negative terminal.

SniperX · 47 Re: Force fan to stay on or add a switch? Wed Jul 12, 2017 2:29 am

SniperX

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Number of posts : 171

robmack wrote:You won't find a ground wire on the sensor. The body of the sensor is the common connection. The body is screwed into the stand pipe which is bolted to the engine which itself is bolted to the frame which is electrically connected to the battery negative terminal.

How is it then that if the temp sensor is short circuited to ground that makes the fan come on, if the temp sensor as you also said that the body of the temp sensor is grounded?

robmack · 48 Re: Force fan to stay on or add a switch? Wed Jul 12, 2017 8:09 am

robmack

Life time member

Number of posts : 2334

The override switch mod is shown in this schematic:

Force fan to stay on or add a switch? Fan-ci10

Note the temperature sensor. It is actually two separate NTC resistors with a common connection that is connected to the threaded body of the unit. Although not shown in this schematic, the body of the sensor is electrically grounded.

When the switch is open, the sensor connected to the temp relay functions as normal. When the switch is closed, the sensor is shorted, and the temp relay measures 0 ohms relative to ground. This is a condition for a very hot engine and the fan turns on.

Is there something about your questions that I misunderstand?

SniperX · 49 Re: Force fan to stay on or add a switch? Wed Jul 12, 2017 2:52 pm

SniperX

Silver member

Number of posts : 171

Looking at that schematic makes me think i can tap into the wire at the temp sensor instead of under the seat. It appears the wire being grounded is one of the two wires directly off the temp sensor.

SniperX · 50 Re: Force fan to stay on or add a switch? Wed Jul 12, 2017 2:55 pm

SniperX

Silver member

Number of posts : 171

What color is the wire off the relay is the switch connected to?

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