been away from bmw's for a while,had a k100lt,a r80rt and just now picked up a 1985 k100 with just 12k on it.
noticed right off the fan did not come after running parked for 15 minutes or so. did al the checks and then when i poked around in the relay box it would come on occasionally. pulled out the temp/fan relay to find 2 pins stll left in the female connector. guess after 26 yrs their solder gave out. soldered them back in and all is well. 1st ride also showed a noisy rear end. found the large ball bearing inner race to be bad. guess all that sitting with no lube splashing around and possible condensatein did a job on it. $85 bearing on the way. love the sound of this thing at around 6k rpm....

Welcome kartooo, from Oz. 12k, if that is real then you'll have a gem.
When you get a chance take her fro a nice long easy run and you will never regret the purchase.
Read the forum on fluid changes and connection cleaning with a new bike, that is a sure way to rule out problems later on
Enjoy
RT

[quote="RT"]Welcome kartooo, from Oz. 12k, if that is real then you'll have a gem.
When you get a chance take her fro a nice long easy run and you will never regret the purchase.
Read the forum on fluid changes and connection cleaning with a new bike, that is a sure way to rule out problems later on
Enjoy
RT[/quote

thnak you,this bike is # 28 in over 40 yrs of riding. i put about 50 miles on it and the only problem i found was the fan,bad bearing in the rear end,dry rot on the rear tire and ngk dp9ea plugs. don't know the reson for dp9ea's.... have some d7ea's on the way along with the bearing and seals for the rear end,rear tire to match the frt will be in the middle of the week.the frt was a perrelli sport demon bias ply while the rear was a michelin radial !! i will be changing all fluids too then ride it all summer. my other bike is a fjr1300 i use for looong trips. gps,electric windshield,electronic cruise control ets ets ets.

Welcome from Oz also.

+1 on what RT said about the electrical connections. Pull them apart, clean them and reassemble. DeoxIT is a preferred choice for cleaning.

blakey wrote:Welcome from Oz also.

+1 on what RT said about the electrical connections. Pull them apart, clean them and reassemble. DeoxIT is a preferred choice for cleaning.

appreciate the info,been using dielectric grease after cleaning for yrs. been a member since march 2010 never posting just digging through the info. thought my telling of the 2 pins on the temp swithcing unit would help another with the same problem. pins E and 9 came unsoldered from the board !!

yeah there nice up there kartoo .......hope you get your stuff soon and get it fixed..... have fun mate

Make sure you fit the NGK's with the little bobbins, as the original sparkplug caps needs them.

I have a follow up problem with my 85 RT. A few will know I boiled up at the traffic jam end of a long trip. Bit of a saga. Turned out the fan was frozen solid, brand new bushes but just wouldn't turn, and the overheat warning light did not come on. Just got boiling fluid all over my daks. Anyhow after follow the "How To"guide and installing a new fan, it still won't come on. I have narrowed it down now to maybe a faulty relay or Temperature probe/connection. I have two questions for the clever people. Can I do a resistance check on the pins of the
Fan/temp warning light relay, and if so what are the numbers, or can they be cracked open to check the points? I have a spare but would like to know if it works as well.
Also as an aside, when I drained the radiator the first time, there was not a crush washer on the drain plug at the water pump, should there be one? I have seen it mentioned but it hasn't ever leaked.
The next step will be to unplug the temperature probe, meaning draining the radiatror again All I want to do is go for a ride!!!.

rt ...im sure there are posts about the temperature probe somewhere on here ....if you find it ...im sure you will be able to measure the resistance reading by picking off the right terminal for a measurement at the switch relay thingy ....rather than removing the probe and draining it .
i think i read somewhere in here that ,,,the earth terminal /reference seems to be a common issue ....i guess all sorts of temperature things could be related.!!!!

as for the crush washer ......hey its working dont fiddle .....but keep in mind there are always crush washers recomended on all sorts of things "bmw" ...i would install one... when next you have the oportunity ...maybe next fluid change ?

RT wrote:Can I do a resistance check on the pins of the Fan/temp warning light relay,

Should be possible according to the schematic diagram. Measure the resistance between pin "E" on the relay (violet/green wire) and ground.

and if so what are the numbers,

Not sure what you meant by numbers here (relay pin numbers or temperature numbers) but I'm assuming temperature numbers.
Excel spreadsheet showing negative temperature coefficient (NTC) response curve

Also as an aside, when I drained the radiator the first time, there was not a crush washer on the drain plug at the water pump, should there be one?

I have one on my drain plug. They are fairly standard and can be had at most quality auto parts stores.

Hi RT. In the manual I have they say the temperature sensor can only be tested by substitution. Same for the temperature sensing switch unit.

Hope you get it sorted soon.

RT, you could always do what any self-respecting backyard 'technician' would do and whack a switch onto it! Cut that silly temp sensor right out of the picture. Take control. Run the cooling fan whenever you bloody well feel like, yessiree. Come to think of it I'm gunna go out there right now and rip off the fuel injection, strap me a water pistol on the end of the fuel hose and squeeeeeze my merry way down the highway! Now for that first cuppa, get the day rolling.

As it happens TWB at 3 am yesterday that very solution struck me, and I was wondering if anyone had ever done it. Now I know it's a Queensland thing I'll give it a miss.
Tks Dave, Robmack and Charlie, all info gratefully rec'd and processed. I actually had the multi meter out wondering which way up it went and the battery died, oh well back in the drawer. I am going to test the resistance between my relay and then my spares bike relay and see if they work, whack it in and heat the bike up.
I'll be in the market for a new ECu I guess ha, wait I have a spare.
Cheers RT

RT, that temp sensor, is it a two-wire thingameebob? To test the fan's ability to run through the relay, and ultimately the sensor, pull the sensor's two connector plug off, switch the key to on, and touch the two connector wires together with a small jumper wire. Does the fan spin? Then it's probably the sensor. I learnt that in Victoria before the great migration North.

Hi mate. I understand it is that simple. HOWEVER it has the same connector clip as an injector, with wire outside springy mongrel clip. And guess what, looks like the radiator has to come off to get at it properly, or get it back on more precise. I have just ruled out the under tank relay, jumped plug No.s 15 and A2 and bazinga, fan on, so
all the circuitry is working right up to the temp sensor. Just took it for a cranky spin and have discovered the secret to fix the problem. Go real fast and don't ever stop. Easy. Waiting for it to cool down now to drain the radiator again. I better find it, as my patience is wearing thinner than my scalp.
tks mate, it helps to calm down when you can look up someone's reply. I'll take some photo's of the route I've taken to get to this point. Might help someone else. The bike's running beautifully otherwise.
RT

Two Wheels Better wrote:RT, that temp sensor, is it a two-wire thingameebob? To test the fan's ability to run through the relay, and ultimately the sensor, pull the sensor's two connector plug off, switch the key to on, and touch the two connector wires together with a small jumper wire. Does the fan spin? Then it's probably the sensor. I learnt that in Victoria before the great migration North.

On a 16V with Motronic this would function, but would also probably store a fault code as 0 ohm
is outside of normal operation range.
The sensor used is isolated from ground, the motronic sends out a signal of 5V+ which travels through
the sensor, and the drop in voltage defines the temp.

This temp. sensor used on the Jetronic also have two connectors, but then it`s a dual element and both
are connected to ground in the other end, and the resistance to ground defines the temp.
One element is used for the relay which operates the fan and warning light.
The other element is used for the Jetronic for calculating the fuel mixture.

Inge K.

yep thats the one he has inge.....been waiting for them to tweek on that ....giggles

what you could do rt is jumper the wire from the sensor and run a switch to ground ....with ...yes i said with..... a resistor in series
ill guess at 220 ohms if your temp sensor is open circuit ....other wise ...maybe a few hundred ohms more if the sensor is sorta working .... this would safely turn the relay on hard and hey presto you have a manual override for fan activation .

it would be good to find out .......remove the connector on pin "e" of the temp relay unit ...measure it to ground (resistance scale ) and get the current temperature ...we can work it out from the excel worksheet above ....


and mate ...want me to send you a brand new 9 volt battery for the multimeter......or a hammer ?

Tks Inge K that may go some way to explain why I'm not having any success yet. Thought I'd put some photo s on to deter/help someone else.

First whilst the fan is still on the bike (unlike the above piccy), I connected a battery via jumper wires, positive to the yellow green wire and negative to the brown wire. Presto, fan worked, can rule it out.

Then after lifting the petrol tank at the rear and jamming it up with some wood, I removed this relay (one bolt/screw DONT DROP IT) and as you can see it has the set out of the pins on the side of it. By following the instructions in the "How to"guide, I took a small jump wire and connected pins A2 and 15 then turned the ignition on. Presto, fan worked, wiring circuit is ok, including fuse. Put relay back in before any more action. (first of course Deoxit everything).


I am looking for the final leg, which I'm told is the Temperature Sensor switch/probe, the one that signals temp rises. To get at it, remove this air
intake hose.

The little sucker is in there, behind the radiator over on what is the left hand side, resting on top of the engine.

This is the radiator/water pump drain plug. Stand on your head to see it underneath the water/oil pump. Do yourself a favour, undo this first before you undo the radiator filler cap under the tank, I didn't and got peed on before I could get a bucket under the drain. Testes bitter fyg.

This is what we are looking for, on a bike I prepared earlier. There is about a centimetre gap under the radiator but methinks that'a 10 swear word job to get undone.

Remember mine is a 2 valve 1985, had two pins on this and I'm about to find out what the story is, technically I could short those 2 plugs on one of them and get the fan running. That is to be continued. But here is me taking the probe out pf my wreck bike with a 19mm ring spanner.

I am hoping to use this one as a backup if that is my problem.

And this is the end of my journey, so far. That is the probe, just got to try to jump the connectors with my real bike now, I have taken the radiator off
and opened that plug up, darkness came early.
Sorry if this is very basic for most of you, but I found the manual photo's pretty pathetic.

Tks Charlie, new battery in hand, no excuse tomorrow. I've outdone my brain for tonight, all those downloads. I feel a red or two coming on.
Cheers Men. We will prevail. It is only a machine.
RT

cheers rt ...have a good nights rest ...... tommorrow when you get lively ..( about morning tea time) ....try and measure between each of those pins /connectors ...and the outer of that probe ...im guessing youll get something.

i'm thinking the earth reference that has been mentioned as being a problem ....is the corrosion between the probe , the housing and the body of the motor its screwed onto (but high resistance ) .... which makes good sence after seeing the pics youve posted ........good work brother ....cheers

Don't forget that while it is accessible remove the outlet stub and renew the O ring and clean all the corosion of the alloy.
I have had that O ring leak on both the K100 and K75 so it is worthwhile checking it.

K Freak, Are you referring to Part number 18 in this diagram as the outlet stub O-ring that needs replacing?



My engine is off the frame for other problems and I might want to do this service item while it's in this state. Thanks.

RT, If you discover that the sensor is OK afterall, then the problem may be within the temperature sensing relay. I had a non-working fan problem last year, similar to yours. My original fan failed and I replaced it yet it did not work on the bike (although it worked when I bench-tested it before the install).

I ran through the diagnostics and discovered that the connector into which the fan plugged was poorly connected. Sprayed it with contact cleaner and reseated the connector several times. Corrosion was taken care of I thought yet the fan still did not function. The overtemp light diags passed, I read proper resistance to the sensor and was able to manually start the fan as I mentioned. Meant that the problem was in the relay. I opened up the relay case and eventually discovered a cracked solder joint in the relay itself which I repaired by reheating the failed joint with a soldering iron. Problem solved. Root cause was that the temperature sensor resistance change was not being sensed by the relay circuit and not turning on the fan because the sensor circuit was open.

You know Robmack I have been wondering if I should have just cracked it open first up, but was not sure if it was possible, the case seems brittle, but I have a spare so prob shud do it. I have a feeling that this probe will pass the test and leave me stranded . If it is the relay I'll kick myself. I read another thread where the fan started working after 19 mins, thats way longer than I have left it
And tks again K freak, I'll attend to that o ring as well. What sort of sealant should I use when I put the sensor back in the pipe? any suggestions?
RT

RT wrote:You know Robmack I have been wondering if I should have just cracked it open first up, but was not sure if it was possible, the case seems brittle, but I have a spare so prob shud do it. I have a feeling that this probe will pass the test and leave me stranded . If it is the relay I'll kick myself. I read another thread where the fan started working after 19 mins, thats way longer than I have left it
And tks again K freak, I'll attend to that o ring as well. What sort of sealant should I use when I put the sensor back in the pipe? any suggestions?
RT

It sure is worth replacing that O ring as it is a lot of work for something so small and cheap if you have to take it all apart again

I use permatex it is an alchol based jointing compound it never dries and is sticky and messy but good, but the main thing is avoid using the teflon tape that gas fitters and plumbers use because if a string of it gets lose then it can wrap around a shaft and it will chew out a seal in no time flat.
Locktite make a good one I think it is called Master Seal I used to use it on all the air line fittings on trucks because you cant use the teflon tape as it gets into the valves and causes havoc like not having brakes etc.

[quote="RT"] If it is the relay I'll kick myself. RT[/quote

Mine drove me nuts too. as stated on my initial 1st post. after checks and double checks of stuff it was the blades on the relay that came unsoldered from the circuiit board. easy fix,the cover just pops off and there is plenty of room for one of them pencil type solder irons.

RT wrote:What sort of sealant should I use when I put the sensor back in the pipe? any suggestions?

Why mess with sealant, as long it`s a sealing washer involved.

Inge K.

Inge K. wrote:
Why mess with sealant, as long it`s a sealing washer involved.

Inge K.

Spot on there I was thinking a tapered thread but it has a parallel thread and a washer so you don't need anything. It may have been the same thing on my Ford that I was thinking of.
What would we do without you.

hey rt ....would you do me a favour ?....could you measure ...with that new fangled multi meter (ohms scale) between the gland (nut ) of the sensor and the battery earthpoint .....when you get it back in of corse

i suspect that there is some resistance between the body of the sensor , the tower (holding the sensor ) and the joint where it mates up to the engine proper ....

just want to see if that is a problem area

thanks mate !!!!

Will do charlie99, tomorrow. So far i've jumped the two contacts in the connector to the sensor and ntg happened. I.m beginning to think
robmack's relay problem may be the answer as there's a problem up the line from the temp probe connector., and with the relay removed
I get fan on jumping the relay contacts. Still have to check everything as i've pulled it all apart.
The only reason I was asking about sealant on the probe was because it says to in Clymers. Got permatex today anyway, just in case. Hope my mother in law's pension comes thru soon, I'm getting strapped.
RT

oh ?!!! what you need to do is jump the contacts to earth rt ...not to each other

the circuit in the sensor is two sensors in fact and go to earth each one + ------- = -------- + and earth is the outside of the sensor when mounted to the housing .

when i got my k100rs (92-16v) in april, i bought replacements for all the hose's, o-rings,seals along with a new thermostat, temp sensor switch and relay. after reading these posts, i was aware that these bikes run hot, but the run back from london (shudder!) to wiltshire was a bit unnerving as the temp gauge was well up .and although these gauges are a bit (very) vague, i decided to have my mechanic replace it all. that being said, it took him a week to get the fan to work correctly, but he was using the wrong (pre-1990) wiring diagram, and kept saying 'your missing a relay, according to this picture' (from the haynes book of lie's and myths) thank god i'd just got the clymer manual!! but at the end of it all, as someone else mentioned on this chain, i fitted a manual override switch on the right hand side fairing inner, just under the temp gauge.

RT wrote:So far i've jumped the two contacts in the connector to the sensor and ntg happened.

Please, be so kind and read my explanation about the sensors one more time.
(you got Jetronic, not Motronic)

Inge K.

Inge K it is not that I haven't read your excellent info, it's just that I have'nt ever had exposure to this electronics stuff ever before so I'm
struggling with some of the terminology. Bear with me and I promise to do some homework.
Cheers guys RT

Skip the homework, we`re in the forums to learn from each other.

Inge K.

Oh Kay, replaced the temp probe with one from my spares bike, in a fit of pique, put everything back together, turned on the engine and within 5 mins, the fan came on.Finally I can go for a spin. except that the rear brake cylinder is now leaking. But still some back door success. Tks for all your advice.
RT

yay ...... what great news rt !!!!! ill bet your thinking thats sparesbike has nearly paid for itself already .


keep the other one mate .....you never know when and if it could come in handy sometime .

dont forget to write on it ...or label it huh ?

Yep tks mate. and I will do some resistance tests to see if I can figure it out. Doesn't seem to me to be too much can go wrong with them. Now I have a puddle of brake fluid under rear master, looks likesomething's happening inside. If only Blakey hadn't mentioned the discolouration of my fluid I would be oblivious, and not stopping I guess. That'll be another thread.
I now have to pull all the useable bits off the old bike as I have gone past the point of no return there. The radiator is better than mine but not undoing all that again.
Cheers RT