Fun might be over......1500 uneventful miles and then a short 15 mile ride in VERY stop and go traffic resulted in coolant spraying out the top of the coolant overflow tank. It definitely covered my leg, but with riding gear on didn't seem to be hot enough to burn me.

Combine this with a failed battery, and I think it may be time to do my due diligence and tear the bike down and give it the proper service it deserved since my ownership.

Is it common for a K1100 to overheat in 100F temperatures, and does it typically pour coolant out of the overflow bottle all over the unsuspecting rider? I did not hear the fan come on, and with my aftermarket Acewell gauge obviously didn't see any indication of an overheat condition. I was able to ride the bike the remainder of the 5 miles home without an issue. Coolant overflow tank was empty when I got home, but the radiator was still full when I removed the cap. The coolant is green with no hints of oil escaping, just not sure where to start my troubleshoot for the overheat condition?

Happy riding guys! Looking forward to any advice that might point me in the right direction.

Christian

Perhaps the fan & temp gauge were not operable because of the failed battery? I think we need more details.
,I think although we know not yet what happened here......we should assume that it did not overheat because 2 different indicators both did not react.
#1 the fan did not start (or at least the driver did not notice it)
#2 the (otherwise dependable??) aftermarket gauge did not indicate hot?
I guess my next questions are: Has the fan been noted to function properly recently?
and up until now, was the aftermarket gauge working in normal ranges?
What is the very recent history of anything changed or otherwise done to the machine?
It is possible, though unlikely that there was some kind of momentary failure of the thermostat.
It is possible that the cooling system had some kind of air bubble that just cleared out? Again unlikely.
The system cap could have been incorrectly installed or had some other failure of the pressure valve within?
I think now, if nothing else is noted.....the cooling syst should be topped up with 50/50 coolant mix and the engine started from dead cold and observed at idle or slightly high idle as it warms up on the center stand.
As the bike idles 10 minutes or more the temp gauge should progress upward normally & continually (perhaps dropping back towards cold momentarily as the thermostat throttles into the engine some colder coolant from the radiator).....watching the temp gauge continually climb till the thermostat is completely open. At that point.....the temp should continue to increase....bit by bit until at some point before boil over the fan should come on and reduce the temperature back down a few degrees. Then the fan cycles off.
In most cases this test could be done with the tank slightly elevated to the left and the fill cap off for observation of the progress.
The only other factor that I know of that could cause coolant to spew out of the tank would be some kind of head gasket failure.....something that won't mysteriously go away once it has occurred.
Without knowing more......I would have to guess that the fan failed to start, but that would preclude the idea that the temp gauge was working correctly.
A complete cooling system performance test is indicated now.
regards.....ibj...

I've just gone over all of CKs posts about this bike.
Seems there is no verification that the fan was coming on normally after his big snafu in trying to find why it would not shut off earlier.
Best guess is that this is the first time he was in heavy enough traffic to require the fan and for reasons unknown it's not working.
Problem is probably with the fan or its control circuitry.
Regards....ibj...

Check the fan first they are known for being unreliable due to water and crud getting into them.
If the fan spins up really quick then check the fan relay will make the fan turn on then check if the relay will turn on then will the sensor make the relay work.
The over heat light and fan circuit are different circuits although they work from the same sensor but even that unit has two sensors in the one piece.
The fan should come on at 103deg C and the light at 111deg C and if over 113 deg C the engine will not start onec it has been stopped until it cools considerably, like well below 100deg C
It is quite normal for the coolant to come out of the overflow container but I consider it a bit of poor design.
The temp relay unit and sensor are usually reliable the weak point is the crappy fan.

yep all quite normal stuff

we have seen many times here that the fan electrical connector has corroded up ...and even when all things are working correctly it just wont allow power to get to the fan .

also check that the fan actually rotates ...get a stick or something and rotate it, the bushes for the fan for lots of northernly folks might not have seen any work for quite some time ...especially if it hasnt been riden in higher temperatures for some time . and this might draw huge amounts of current through the electrical connection causing it to fail ...erm more.....from a stalled motor, when it needs to work . (note this can also affect the brushes to the fan motor ... so sometimes a good check is to apply power to the fan connections directly and see the result )



ibj ...the bloke just said he has a after market instument cluster ...how is he going to test the way you propose ?

we have seen that the bmw guage is quite "expanded scale " in relation to standard types we might see quite a bit of change on the "original guages " but let me make an observation ... that it all happens in about a needle width of a standard guage (when the thermostat starts being operational at about 82 c ).

most folks would be unable to plug a guage in and get what you describe . (dont forget the bmw guage sensor is at the water pump and not the radiator )

perhaps a remote sensor type meter (oven type temperature thingy ) with the sensor mounted about where the thermostat sits on the lower right of the radiator and just above the thermostat (not at the top of the tank or the feed from the motor ) could be a place to observe the temperature changes ?

the bypass pipe is operational till the thermostat closes off flow through it and passes the fluid through the main core of the radiator ....there is a region of this activation when a mix of radiator and bypass fluids are happening

the sensor in the water stub is a 2 pronged thingy ....a prong for each side of the sensor (its a double sensor in one housing ) and the ground connection makes for 3 connections ....remove this plug and clean up the contacts to BOTH prongs to be absolutly sure that all things are good feeding the efi computer and the temp sensing relay (which turns the fan on )

this temp sensor at the water stub really has no direct relation to the actuall thermostat temperature or operation ...but obviously if the flow slows and-or cooling is not acheived the temperature comming out of the engine will increase causing the relay for the fan to start ...and the electronic fail safe motor inhibit to be operational as the temp increases . and lots of fluid escaping via the under tank water cap and resevoir route .

rick outlined that verry well

unfortunaly if its fairings are on, its off with the right hand side cover .....and remooval of the airbox to get a real good go at the water temp sensor and the fan connections ....unless you pull the radiator off ...(best option )

just some observations that we have seen over time

hope it helps cafe k

Everyone is entitled to their opinions and I respect yours as well. I do feel that it was unfair to criticize my general information about how to go about seeing if the cooling system is operating.
We are all friends here are we not?
I understood that he had an Acewell temperature gauge. Unfortunately, I don't actually have experience with that unit.
I assumed from the original post that it is a gauge.... and that it has a way to indicate the temps.
My experience shows that often, not always, the temp gauge will recede momentarily if a slug of colder water is admitted suddenly in to a warming engine by the thermostat. My intention was simply to have him not be alarmed if that did happen to occur.
I would suggest that he warms the vehicle up and attempts to verify that the fan does or does not indeed function before doing anything else including disassembling the machine.
My bike is an rs and I have no experience with the other models.....so I can't really speak to how much work it would be to access the fan/sensor area on his 1100.....
So, only speaking from what I know, on my bike, It would be far easier and less problematic to remove the right side fairing lower and the entire air box (10 minutes max.) than it would be to open, drain & refill the coolant system to remove the radiator.
I think we both agree that his fan probably mal-functioned. How He (and you) go about addressing it is your option..
Again, I'm sorry that I could not foresee that his temperature gauge should have been expected to work as I surmised.
My error.
Regards...ibj....

hi ibj ...no problem here ....i have no issue with the diagnosis method you suggest to employ ...nor the reasoning , just the tools at hand for the owner .... having already said he had aftermarket equipment installed . it wont neccesarily be calibrated for our particular machines ...and he may not have the equipment ( including an overheat indication - warning lamp, fitted to the standard trim, instrument clusters ) that we have to act as a reference regarding your detailed explanation

i appoligize if you saw my post as a smirk or deflamatory comment on your opinion, it is not meant to do so .just to remind folks that it is far too easy to assume that everything is stock standard .

many folks seek alternatives from the "as produced " machine and dont have the same information to hand at a glance, there is no fault with that at all.

we try to offer support and help them understand the workings ......and in almost all cases the combined effort is taken on board ...and success is acheived .

G'day ibjman
I was interested in this post, and after reading all the replies in this thread I didn't think your reply was any less informative than Rick G and Charlie 99. I'm just glad that all you blokes give great informative information that benefits all K Bike owners resolve some of there problems.
Regards Smithy

I would just like to add that the dual element temp sensor is only present on the
Jetronic equipped models (2V).
The sensor used together with the Motronic unit (4V) is not connected to ground,
and the prongs is each end of the resistor.

The Motronic unit sends out a 5V+ signal, the voltage drop determines the
measured actual temp.

Gents,

Thank you so much for all of the great advice! Good news for me is that my K is in a naked configuration so there really isn't that much work involved in getting at the pieces I need to in order to diagnose the problem.

To clarify, I do not have a stand-alone temp gauge on the bike right now, and unfortunately the Acewell 2853 does not provide an engine temp indication either. I have been relying on the fact that the sensor is working correctly and riding without any temp indicator at all After this last event I already have a stand-alone temp unit on order especially since the summers in Reno, NV get pretty hot!

I'm going to power the fan directly to make sure that it spins up. I do know that with my previous faulty Motronic unit the fan would spin up as soon as I turned the ignition on. Based on the advice I think my next plan is to attempt to duplicate the problem. Am I correct in presuming that I should be able to get the bike fairly warm by letting it sit and idle in my garage for 10 minutes or so?

I had thought air bubble that caused the fluid to spew out initially, but for now I will be replacing the battery and attempting to duplicate the problem to help me further diagnose. Thanks again for all of the great responses and I will be sure to post my results here shortly!

Thank you all for your kind comments! Perhaps ibj...was just having an off moment!
You should work on verifying fan performance and control circuit BEFORE trying the test simply to avoid spewing coolant all over again during an overheat situation in the garage.
I think it's almost a virtual certainty that there is a problem with the fan circuit. Going further out on a limb......I would bet that the fan motor itself will be found operable siting the fact that it worked recently. On the naked bike you may be able to just reach in and give it a spin with finger before doing anything.....would at least verify that it turns.
I fully expect you will find the defect somewhere in the actual wiring where some error has been introduced during work at some point such as a cut/disconnected or wrongly connected wire. it Should be a reasonably simple matter to "trigger" the fan relay manually to verify that the circuit from the relay through the fan operates. If that can be verified..... then you would be down to correcting the control circuit for the relay. If not, then you can probably target the problem to the previous.
The first move is to be sure the charging syst. and battery system are working properly??? The fan & control circuit can not be dependable at sub 12V levels. Could the dead battery be caused by a charging system fault/error instead of a faulty battery?
I've seen a LOT of useable batteries replaced simply because they had become discharged. Doing so creates more diagnostic errors down the line when the new batt starts to get low again.
Start the bike, put a volt meter across the pos/neg battery with the engine running at fast idle.......you're looking for 14V or there about........ Maybe it would take a while to climb to that if the battery is low.
I was always taught that it takes 14.2 to 14.6 to create a fully charged battery. Experience shows that euro stuff is often substantially lower than that.
If you measure batt. voltage before you start........you should see a definite increase from that once the alt. starts charging.
As to system testing....It is possible to buy a "non contact" infra red thermometer for not too much money,
http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html
that when pointed at various places on the machine......radiator top & bottom areas, engine water outlet, water pump neck, etc would give you a good idea of what should be happening about when during the test.
It will always be a handy item in your tool box for checking stuff around the house later.
I have to go ship some just sold parts, so I'll check back later to see how you are doing.
Let's get this thing all fixed up so you can ride it up to Salem in July!
Regards, ibj.....

thanks for the correction inge ...i missed the k1100 bit and did the deal for the old 8 valve 100

I have had this problem on my K1100LT and it turned out that the fan was seized solid - replaced fan with a working unit and all was resolved. I had exactly the same issue with my K100RT whilst touring Europe 3 years ago. We hit Monaco at rush hour in 40 degrees (in the shade) heat and my coolant expelled itself all over my right leg. I just made sure that I carried water for top ups and didn't get stuck in traffic again from then onwards. 4,000 miles later I reached home in England and replaced the fan unit and it has been fine ever since. The fans do seem to have a tendency to sieze solid in our colder British climate due to never really cutting in at all.

charlie99 wrote:thanks for the correction inge ...i missed the k1100 bit and did the deal for the old 8 valve 100

So did I. Must be because we are upside down Charlie
So we have to write out 100 times
I must read posts more closely.

Quick update on my progress......tore into the bike more than I had planned on which always seems to happen :-)

The fan works just fine when powered directly. I tried to run the fan test by grounding pin #1 on the diagnostic plug for 10 seconds, but no sign of life from the fan at all. I also idled the bike for about 10 minutes with no sign of life from the fan.

I am planning to do a couple of things....my coolant overflow will be moved forward behind the radiator with an overflow hose routed under the bike so I don't get a nice coolant shower if this is to happen again. I'm also considering adding a manual fan switch so that I can turn the fan on when I am in stop and go traffic, but then shut it down when on the freeway etc...

I am also going to purchase the infra-red temp tool so that I can check/diagnose the bike a little more accurately. In the meantime I'm going to continue to troubleshoot the fan circuit. Seems like a fairly simple setup so I don't think it should take me too long to get it figured out.

Maybe since this bike is new to me and I'm not sure what the PO did a full fluid change including radiator flush may not be a bad idea?

Thanks again for all of the help guys!

Sorry forgot to mention that the charging unit on the bike seems to be working fine. The battery on the other hand is going to be replaced. Perhaps when I have a new battery in the bike all will be well with the fan circuit?

You will find many opinions on this. Some people like having a fan switch so that they can "test" the fan motor as part of their walk around inspection before riding or to "exercise" the fan motor so it doesn't get bound up.
I respect their reasoning and motivations.
I would highly recommend however that you resist the urge to add a switch. There are a myriad of reasons.....but I don't want to start a BIG flaming discussion on the forum.
I would strongly advise you to continue your education in developing effective and common sense diagnostic methods.
Do not wire around a problem. You can fix this!
Please don't add a bunch of extra wiring and introduce a whole host of new vulnerabilities for future failures and extra complexity to any issues you already have.
I have always been a proponent of the "Stay Stock" Philosophy.
Similarly, please refrain from altering the reservoir till you have all the problems sorted out.
The issue you had with the spewing coolant is very rare as these machines rarely overheat. Once you have the fan working.......moving the bottle won't be of any use and once again introduces the possibility of creating another unseen issue.
Later once you are very proficient and have some big miles under your belt on this particular machine... if you feel the need to add a useful accy. I would not complain.
(Was I correct in remembering that one of the 1st things you did on the bike when you received it was to add/change LED lights???? ) Cool I suppose, but did you NEED them, now?
Just my opinions.....take it for what it's worth.
Oh, By the way......you don't need a washable reusable air filter either. They are designed with the "Fishing Lure Syndrome" built in.
I think you are learning a LOT and I wish I had experience on your 1100 model to help more, but I have none.
I really want to learn what was the actual cause of the problem if you can find it.
Testing the engine for 10 minutes is not long enough to start the fan. However, in this case.....since the fan doesn't work, no amount of time will get it to run till the fault is corrected.
Regards, ibj...

About checking the relay and related wiring, have a look at this thread.
It's valid if your bike is a -93 year model or older....

Cafe-K,
I once had an overflowing coolant tank which was caused by a split in the hose from the radiator to the tank. When the engine warmed, the coolant flowed normally to the tank, but on cooling, it drew air via the split back into the rad.
Maybe worth checking.
Paul.

I haven't seen the wiring diagram for this model.........But is it at all possible that by eliminating the factory speedometer (if that is so) that being without the "Hot" warning light circuit.......that the fan won't trigger?
He has the Acewell unit, correct?
Also....it seems odd that he had problems with the fan NOT turning off with the old ecu and now with the replacement ecu he has the opposite problem.
Common sense says there is some relative clue there.
What about it INGE????

Haven't looked that close at all posts, haven't noticed that the ECU allready have been changed.

Could be that he's being unlucky with both ECU's?
Have also seen on other forums that it's often is a problem with this specific circuit on the Motronic units.

Hope I'm not unlucky with both ECUs but can't rule that out until I've completed the tests that Inge recommended.

ibj....I agree that stock is best especially with the engineering at BMW. I hope that I can report a properly functioning fan circuit here shortly.

Paul thanks for the info about the hose. Mine is definitely old and dried out so overdue for replacement.

Inge thanks for the diagrams regarding the fan circuit. I'm about to head out and ground pin 16 to see if the fan comes on.

Hoping to have a properly functioning machine here soon. I appreciate all of the input!

Or.....could a shorted circuit somewhere damage his ecu's?

Cafe-K wrote:I'm about to head out and ground pin 16 to see if the fan comes on.

And your bike is a model year -93, or older?

It's the early generation 93 right before they switched over to Motronic 2.2 I think?

Okay guys grounding pin 16 on the motronic ECU caused the fan to come to life......seems like the signal then isn't coming from the computer....hoping now I can narrow it down to a sensor issue rather than a computer issue.....

Before I blame my Motronic unit for this issue......is it possibly the fact (as ibj mentioned) that I have replaced the stock dash with the Acewell unit which does not include a temperature circuit? Perhaps in my wiring harness I will need to make some sort of modification to let the bike give the Motronic unit the signal to kick the fan on?

Based on the fact that when I grounded pin 16 the fan came on means that everything from the computer forward appears to be working as advertised. I'm thinking then it has to be my temp sensor or something to do with my aftermarket gauge?

in most of the bmw electronics , they have a transistor to turn on external components ..ie relay and lamp etc

i wonder if (like the bmu ) internally to the motronic unit, that transistor has had a hernia and now fails to work ....and thus the relay no longer activates

could this be because the wiring has been modified from the old guages and the cables in question have had a short circuit condition ?

or does the bulb in the warning lamp provide a path of voltage to the relay output control electronics ...in the motronic unit ?

would love to see inside one ....and see the circuits inside

probably, if this was the case , a replacement transistor could be got and installed ....but by someone competent in doing such things .

charlie99 wrote: ....but by someone competent in doing such things .

That would certainly be not me!!!

So I'm in agreement with ibj about not straying too far from stock, but if the verdict ends up finding the ECU to be guilty, then would it be reasonable to solder in a $5 switch to manually operate the fan rather than replace the ECU in the meantime?

I also really want to find out what would be causing the short if that were to be the case as well. The circuit as far as I know just involves the temp sensor (which has not been messed with). The engine harness is new....the instrument and electrics harness has modifications, but care was taken to avoid shorts with wires that were not needed by the new Acewell gauge....I'm still thinking there could be a wire in that bundle somewhere that needs a connection to complete the fan circuit to the ECU.....(hoping)

Cafe-K wrote:....I'm still thinking there could be a wire in that bundle somewhere that needs a connection to complete the fan circuit to the ECU.....(hoping)

It's no need to search for any missing connections.......
As your fan starts when grounding contact 16, the circuit is complete.

Prognosis is bad ECU then?

Looks like the problem is in the ECU internals.

But it could be a idea to check if the engine really reaches
the high temps, and not spewing coolant caused by a bad cap.

True.....this is a really tough problem to diagnose correctly since I didn't have a gauge to show me that the bike had overheated. Could have been something like Paul mentioned or perhaps an air bubble in the system....darn it.....well like I said I have an engine temp gauge on order so that will help me.

In the meantime I am also waiting for my infra-red temp gauge that ibj recommended to get a better idea of what's going on. Should probably put the bike back together and take it around the block for a few small test rides.

A engine temp gauge is a good idea, as long it's connected to the correct sensor (as Charlie allready have mentioned).

You could also look for the warning lamp wire...among the wires going to the old instrument......brown/black wire,,which grounding the warning lamp.

Would it be possible to wire that into an LED on the acewell gauge such as the hazard light? If I could do that it would keep the setup very clean (like I want it to remain) and also add functionality to my gauge.

Or you could tilt the tank to the side, take the fill cap off, put your wife's meat thermometer in the coolant there and start it up. Observe the temp as the bike warms up. When it get's to 200 deg F, the fan should have come on. If not, you still have issues.
Would it not be unlikely that he had 2 bad ecu's in a row?

It is highly unlikely that the light and fan circuit are connected in any way except that the same sensor is read to give temperatures as the fan comes on at 103degC and the light at 111degC so the light circuit would not be a ground for a fan relay or similar sort of action.
There will be a switching transistor for the fan relay in the ECU and that is the most likely culprit but which one it is will be unknown unless it is obviously fried.
Short the 2 wires at the sensor and that will bring the fan and light circuits on as a short probably would represent a temp of 250degC. Yoy could have a sensor that is slowly going out of range but still lets the bike run normally but wont switch the fan.

I'm sorry Rick just trying to make sure I'm understanding your suggestion. I should short the wires at the sensor themselves? i.e. unplug the sensor and short the connection to see if that spins the fan up? If that is the case would that be an indication of a faulty sensor? Thanks again!

Yep that's right. The hotter the engine gets the lower the resistance of the sensor gets so with a short on the two wires the computer reads that as a big overheat and starts the fan.
If that works then test the sensor out of the bike and at cold it should read 2000 - 1500 ohms maybe higher if it is really cold and in boiling water around 60 ohms but if in boiling water you get say 300 ohms then it is probably had the gong.
They would be around the right figures, I cant find the actual readings anywhere but someone will come along and say here they are

Thanks Rick. I think that is the definitive answer I've been looking for. If I run that test based on the things I've done so far, and the fan fails to spin up I can conclude that I have an ECU problem. Also, regardless I want to make sure that my sensor is working correctly, but from my readings it seems that these temp sensors are pretty reliable?

Again, I will post my results when I have completed my troubleshooting.

Final note.....I know I'm a black sheep here because I am a K1100 guy but I have looked into the other forums and I much prefer the crew here. Put up with me as long as you guys can!

That's one of the most wonderful things about this forum!
There are no Black sheep here! Heck, these guys even put up with a "loose canon" like me!!!
We're all family here, and besides that we all learn a lot when you solve your problem!
Hang in there you have lots of wonderful miles ahead.....be it 1000, 1100, or a 50.
Regards, ibj...

Cafe-K wrote:Thanks Rick. I think that is the definitive answer I've been looking for. If I run that test based on the things I've done so far, and the fan fails to spin up I can conclude that I have an ECU problem. Also, regardless I want to make sure that my sensor is working correctly, but from my readings it seems that these temp sensors are pretty reliable?

Again, I will post my results when I have completed my troubleshooting.

Final note.....I know I'm a black sheep here because I am a K1100 guy but I have looked into the other forums and I much prefer the crew here. Put up with me as long as you guys can!

They are good I have tested quite a few because of problems but they have always been good it is sometimes the connections and Charlie had one sensor that wasnt earthing well due to corrosion but never a bad sensor itself.
I know the dealers do come avross them but they see many more than me.

How can anyone be a black sheep? The K100 morphed into the K1100 by way of the K100 16v. The 16v seems to have more in common to the 1100 than the 100.
As an owner of a 16v I must be a grey sheep between all the white and black ones.

I was going to short out the connecter as per Rick's recommendation today, but as soon as I unplug the temp sensor and turn the ignition on, the fan comes on. This is with the Motronic unit plugged in. I am presuming that the ECU is seeing an open circuit there which is the same signal as when the bike gets very hot? This is causing the fan then to kick on with the temp sensor unplugged?

So that may point towards a couple of things. This means the system is working as it is supposed to be? Next step for me then is to remove the temp sensor and test it manually with my multimeter by immersing the sensor in various different temps of water and recording the results?

Another possibility of course is that the bike never overheated and the cause of fluid spewing all over my leg was something unrelated to this system?

I have yet to replace the battery, I just keep nursing the existing battery back to life with my tender, but that is the next step. Then I think it's just going to be time to put the bike back together and rebuild that confidence.

The day before the overheat issue I had done a 100+ mile round trip, but that was at freeway speeds and I am sure the cooling system is more efficient in that circumstance.

Thanks again everyone for the support and recommendations, and in the process of diagnosing this I have learned a great deal about my bike which is of great value.

Yes, It takes very little "ram air" across the radiator to keep the fan from being required.
I live in Phoenix, AZ and even when coming off the highway and stopping in local traffic stop lights at 100 degrees outdoor temps......the bike will idle at a stop light for very long time without requiring the fan.
I'm curious about the prior recommendation by others to short the sensor wiring. It seems as if that may have been incorrect???? Based on your observations.... could it be High resistance that indicates HOT rather than low/no resistance????
It still remains a mystery to determine what occurred.
Any chance the reservoir tank was originally simply too full when starting out cold???????

I am pretty good about checking fluid levels before I set off on the bike, and it has never shown me leaks of any kind so I haven't adjusted the fluid level. I glance at it to make sure that the coolant is between the low and high marks, but that's about it.

I think it may still be a good idea to do the resistance check with the temp sensor since I have the bike apart anyway.

I agree.....You could start now by getting a cold reading with the bike at rest.
Theoretically, you have tentatively proved that the fan operates at High resistance (open), hence the current resistance at the switch cold should be very low?????.
I'll interject another bag of worms:
Is it all all possible that the PO has installed a Motronic (2 resistor) switch in your Jetronic (single resistor) engine???
One would think that the 2 designs would have a completely different harness plug connector to prevent that?
I could show you a photo of the 2V early switch and harness plug, but I have never seen what you have.

ibj I have the 93 K1100LT with Motronic 2.1. I have never removed the temp sensor (yet), but the Motronic wiring harness plugs directly into it and as you mentioned I'm not sure if the Jetronic unit is designed differently to prevent interchange.

It seems that the temp sensor engages the fan with high resistance as you mentioned. I presume that I will find very low resistance with the bike cold when I grab my meter.

waiting to hear more:?:

Okay guys with the multimeter set to 20k Ohms I get a reading of 2.15~ and that's with the bike cold.....well 80 degree ambient air temp, but the bike is in the garage sitting in the shade water at room temperature. Does that sound correct?