first place i am new at this forum and so HELLO GUYS. i know this forum 3 years ago more or less its a very usefull place to learn about k100. Now i have a problem when today after 3 weeks in the garage i went to a ride. Like i always do i took the bike outside and start it up to let warm a little while i was dressing my jacket and put the helmet; suddenly the fan starts working,the temp gauge was on red, the overheating light is on(first time i saw it) and than i switched off. i was looking for any problem (the temperature is on the blue normal for 2 or 3 min warm up) but when i tried to start again at the same time the fan works,temp on red and light on when i push the start button and it didn't start anymore.Three weeks ago i took a ride about 400 km and since than the bike was stoped the only thing i did was charging the battery 4 days ago . please anyone can help me and tell me what is the next step.THANKS FOR EVERYONE.

When you tried to re-start how soon after the light on and fan running incident was that? There is a circuit to prevent you starting an overheating bike you can drive a bike which is running and has an overheated engine but you can't start it once stopped until it has cooled down. What is the level of coolant in the radiator?
Regards,
K-BIKE

it was a question of 1 or 2 min time enough to see anything wrong but its not the case.engine temp after i put my hand on it was about 30/40c degrees, normal for the time it was working. there wasn't any overheating .When i push the start button again to restart the engine the fan ,light and gauge were crazy again but it didn't started anymore, this is the problem ,it was an indication of overheating but there isn't any reason .for that. Iam trying to explain best i could.SORRY ABOUT MY ENGLISH I HOPE YOU COULD UNDRESTAND THANK'S K-BIKE

Hi Paulo your English is 100% better than my Portuguese which is non existent so good on you for your effort.

OK Two issues first the indication when the bike was below temp and the non restart. Simple explanation of the non re-start. To protect the engine the Motronic will not allow you to restart the engine if you have an overheat alarm but to safeguard the rider it will allow it to run till you get the bike to safety such as a problem on the fast lane of the motorway they did not want to strand a rider with a dead engine..

I would check the earth from the cover where the temp gauge is mounted and remove the bolts one at a time scrape the metal clean put copper anti seize under and torque back up. Also check the frame to bell housing earth and clean the paint away and put the copper anti seize under and re-torque. That should fix it because if there is a bad earth the bike thinks it is overheating. Also check all the other bike earths at the same time especially frame to engine earths and do the under tank earths with DeOxit.
Regards,
K-BIKE

hi k-bike. after the bike switch off i stored it on the garage and after 6 hours it was already cool i tried to start again but nothing, starter is ok,i ear the fuel pump and any signal of explosions. today first thing in the morning i tried again the same hapens. i checked the cooling level on the radiator was ok,i check the spark on the plugs ,yes it has spark, the only thing i didn't check was fuel in the injectors maybe tomorrow.i ask you if the problem would be temp sensor or temp relay ,what do you think about that?

k-bike please explain me where is the bell housing earth? thank's again. paulo

Hi Paulo,
The temperature sensor has a well known problem which is poor earth so check the earth to the sensor is good. The temperature sensor sits at the front of the engine by the radiator hose and is screwed into a housing check the bolt which holds the housing onto the engine is clean underneath and has some copper anti seize under before you re-bolt it down. Check all earths on the bike for good connections. See the electrical circuit diagrams in these pages there is one which shows the earths make sure they are all good clean connections. My favourite after cleaning them with very fine abrasive paper it to treat them with DeOxit contact cleaner then bolt them back to the chassis. Unless there has been re-wiring by a previous owner brown wires are earth wires and where you see wires bolted to the frame that is the earth point clean them and treat them with contact cleaner.
Regards,
K-BIKE

Normally you have two main earth/ground points on the K's. One is on the centre frame tube untherneath the fuel tank. You'll have to lift the tank, but as you are already checking the radiator you have the tank off (as you didn't do your check on the reservoir, did you??). The other one is on the left side of the bike a little bit aft of the starter motor (two black wires?). Mostly you'll find two wires on the aft one, of which one is actually connected to the ones underneath the tank.

hello guys. i'm glad with your interest to help me, it is in portugal 11.30 sunday morning , beautiful day outside and no bike, now i'm going to the garage after read your replies to find ,i hope so, any earth connettions problems in my k. it's the first time i'm not able to start my k in 4 years, strange for me as it always starts at first push button everytime.i like that bike and my family too at this moment it's the main issue at home and they are all very sad .anyway thank's both of you k-bike and reneZ.

Paulo, how old is your bike? It's important i.c.w. the wiring of the fan/high temp light.

it's a 1986 k100 rt vin 0093042

OK, if I'm right that means you have the coolingwater sensor with the two wires, one that goes to the ECU (LE-Jetronic) and is wat you measure on pin 10, the other wire goes to the temperature relais (bigger, almost opaque relais on the right side in the relais box). The sensor works as an NTC, which basically means that the resistance of the sensor drops if the temperature rises. So the electronics react to a low resistance. This means that a short in the sensor wiring could let the electronics react as if the engine is overheating.
However, appreciating that the temperature sensor for the gauge is fitted on the pump it means that your "Fan on/red light/high temp indication on gauge/ECU acting as if the engine has overheated" means you really have an overheating engine.
For it so suddenly to happen I think you might have a headgasket leak. If this is the case I expect boiling cooling water/loss of coolingwater/frothy oil/oil on cooling water/cloudy oil (not necessarily all at the same time). Do you see any of that? At the time of 'overheating' could you still touch the engine; was it realy hot?

no i didn't saw any of that,at the moment i switched off the bike, find any thing wrong,wait a little 1 or 2 min and when switching on the ignition key the temp gauge was on the blue area, as i did already felt the heat on the water hose seems like 30/40c degrees more or less the normal for 3 or 4 min working but when i tried to start it up pushing start button fan works lights on and temp on red but didn't start anymore. yesterday i tried for the last time put it working, starter is ok fuel pump ok but nothing happens with fan,light or temp gauge and sign of explosions in the engine none!!!!!!!!!!!

OK, bit confused here.

When you had the fan and high temp light on - did your coolingwater temperature gauge also show high temp? If this happens the bike or really overheats or you have an electrical problem that affects all. Specially your last info seems to prove that.

There is a history of very strange electrical issues when the starter motor brushes are gone and/or the collator of the starter motor is very dirty.

ok,i'm a bit confused too. i have just arrived from garage where i maybe checked every earth points i could see and everything seems ok,i tried start up again and nothing changes,before i walk away i put the battery on charge . about the starter motor i did already change the brushes 2 years ago for precaucion but it always worked well and still works today. could the spark plugs be flooded? i checked already if there is spark on the ht leads and yes.maybe any problem with temp switch unit or water temp sensor, i ask you if there is ignition and it doesn't start problaly there is no fuel on the cylinders! what could cut the fuel? thank's rene

Hi Paulo,
Whip out the plugs and have a look at them to see if they are wet or dry and or fouled. When it won't start a check of the plug immediately after the cranking on a cold engine will instantly tell you if the injectors are running because the plugs will be wet with fuel. They need to be dried with a flame and the engine needs to be turned over whilst the plugs are out with the fuel pump unplugged so that the excess fuel gets blown out the plug hole. Many people Bert and I included also have used a flame at the plug hole to dry them out but I could not recommend you do that in this risk averse world in case you burn yourself.

When you say you checked the earth points what did you do look at them or take them apart, clean them and put them back? Did you clean up the bolt on the temperature gauge housing? Bear in mind that was from a tech bulletin from BMW so it is likely to have been a reasonably numerous problem for them to issue a bulletin.

Basically as Rene says the sensor is two sensors in one with two wires and earths through the engine so as to enable the respective circuits to measure them. To do that they both rely on earthing the sensor via the housing it is screwed into. A quick and simple check you can do without risk is to get a test light (every motorcyclist needs one of these and they are cheap or you can make one up with a spare indicator bulb and two wires.

First unplug the sensor wires from the sensor this is vital. Next connect one lead from the test light to the + on the battery (make sure the battery earth leads are connected and the other wire to the test light bulb touch it onto the engine on a non painted bit the bulb should light that checks the bulb can light and how brigth it is. Then put the wire on the sensor body not the two terminals, the bulb should light at pretty much full brilliance if it is dull or does not light you have found a high resistance in the connection from the sensor to the engine and that is what needs to be fixed by cleaning under the bolt and putting some copper anti-seize there and tightening the bolt. The bulb should then light.
Connect all up, make sure the fuel pump wire is plugged in under the tank replace plugs and have a go starting her.

hi k-bike and rene.IT WORKS AT LAST but helping with another battery witch gives enough rotation to start. today i was able to see what hapens with calm. the bike starts dificult ,headbeam is weeker,after 2 min working the same hapens again,fan,light etc, i stoped and when pushing the start button before it works it hapens,i leave it and i could ear a click at the relay box at the same time the fan stops light off and gauge normal.there was no overheating and no pressure at the water hose, it was tepid. when it was cold it starts and nothing goes wrong,it begins after 2 min. it seems to me that something eats battery energy? i saw the alternator voltage and ok.any light you switch,brake,dash, flash does the things worst.i hope you understand my english .i'm waiting for yours opinions .thank's

Hi Paulo,
Good news. The alternator will not charge the battery at idle, if you have a low battery leaving it idling just runs the battery down mor. You need to be running at about 2000+ RPM to charge the battery. Do not try to start with a flat battery the common thing that happens is the starter relay welds shut and it will not stop cranking even when you switch off. If that happens a firm whack on the side of the battery box will often cause the relay to unstick. If you have a motorcycle battery charger put the battery on charge at least overnight and if it is a fully automatic type intended for bikes you can leave it charging whenever you are not riding I do exactly that. So do not let the bike idle start it and drive away as soon as you can. And soon as you can clean all terminals in the bike they have been there for a lot of years.
Regards,
K-BIKE

Hi Paulo,
That is great news if you have an electronics shop try to get some DeoxIT http://www.caig.com/ to treat all plugs and sockets.
Really pleased for you.
Regards,
K-Bike

Great stuff, happy you found it!!

ok just a thought check the resistance of the sensor as it warms to make sure it dosent short out at the time of problem occoring. had a few ect sensors muck up at work cousing misses flat spots ect, but as described of how the sensor works if the sensor is flat shorting at 30deg it could cause this problem,

hi guys. alex it`s possible your thought maybe right, but since i found my problem the bike works fine and i have no reason to check anything else and i hope it wouldn´t happens again,thank you anyway

regards
paulo k100

sorry i really gotta lern to click on the 2nd page b4 i comment lol.