Hi Everyone,
I have owned my 1985 K100RT only for a few weeks but have noticed the temperature warning light does not come on when the ignition is switched on. I have removed the instruments and the bulb is O.K. Is this a common problem? How do you test the sender unit to see if it is O.K.?

mine doesnt either steve

Nor mine.
Paul.

That is correct I suspect they could not be bothered to find a work around for the over temperature light disabling the start when it is on just to enable bulb test. The over temperature condition is quite clever, when it happens it does not cause the bike to cut out but it does prevent you restarting the bike. That characteristic is used in the BMW K factory alarm to prevent the bike being started.
Regards,
K-BIKE

Hi,
So all is O.K. and that is how it is mean't to be. I can't think of another vehicle I have owned in the past with a temperature light instead of a gauge that did not have the light test when you turned on the ignition. Thanks K-BIKE for the information.

K-BIKE wrote:The over temperature condition is quite clever, when it happens it does not cause the bike to cut out but it does prevent you restarting the bike. That characteristic is used in the BMW K factory alarm to prevent the bike being started.
Regards,
K-BIKE

Sorry to interrupt, but I`m not too sure about that.

The overheat start protection is triggered via the second element in the temp. sensor
which is connected to the L-jetronic unit (to calculate the mixture).

The two connections at the temp. management relay is just "spliced in", just a coincidence that is just at this spot.....to keep the wiring neat I guess.
Could be anywhere in the same circuits.

Terminal 31 is just a ordinary ground connection.
Terminal 15 is coming from LSR via fuse 7 and is just connected in front of the
contact to the internal relay which feeding the fan motor, nothing else.

But if the last circuit is powered up (ignition on) and the alarm is armed, it would
trigger the alarm.

Inge K.

You beat me by 10 minutes Inge.
Also I believe there is an engine cutout associated with the overheat function but is higher temp that the no start function.
A friend got caught in bad Sydney trafic recently and it overheated badly and stopped but restarted after cooling to around 200deg F. I haven't been able to find anymore about it but as we all know BMW do play the cards close at times.

When I boiled in City traffic, no light, just hot steam up my thigh. I left it for an hour and she started again. (at the time my fan was not working unbeknown to me) I still don't know if my temp light even works.
RT

RT wrote:When I boiled in City traffic, no light, just hot steam up my thigh. I left it for an hour and she started again. (at the time my fan was not working unbeknown to me) I still don't know if my temp light even works.
RT

Then it might be a good idea to check the sensor, the relay and all the related
connectors and wiring, I`ll guess.......before any top end problems.

Inge K.

I replaced the sensor and fan but still haven't seen my temp light. I refuse to go in there in case I upset something else.
RT

RT wrote:I refuse to go in there in case I upset something else.

Shouldn`t be any problem RT, it isn`t any spark plugs inside the relay box.

Inge K.

you can test the relay by shorting out the sensor lead ( to earth ) that leads to the temp relay ...this should turn the fan on ...and make the temp light illuminate .

of corse this wont prove that the sensor is working properly ....

but you could test the computer under seat connection (pin 10 ) and see that it goes from over 2000 ohms when cold to something around 200 ohms when warmed up ....if memory serves me correctly the magic number to turn the tempsensor on is under 175 ohms

charlie99 wrote:but you could test the computer under seat connection (pin 10 ) and see that it goes from over 2000 ohms when cold to something around 200 ohms when warmed up ....if memory serves me correctly the magic number to turn the tempsensor on is under 175 ohms

I`m do not quite following you on this one, Charlie.
Could it be the fan you have in mind, as this should start at 175 ohms but triggered
from the other element in the temp. sensor?
The same element (and the relay) also manages the warning light, which should
show up at 143 ohms.

Inge K.

yes inge ...i was thinking that the other element would just be a good idea and easy to measure ...but the element going to the temp sensor relay is obvioously the right thing to measure

oh ! 143 ohms for the lamp ? i have a switch to short mine out as a fan over ride .....which of corse turns the lamp on as well (intermitent use )

charlie99 wrote:oh ! 143 ohms for the lamp ?

With some (rather wide) tolerances....

Fan should start at 103^oc +/- 3,5^o on 175 ohms +/- 10%.
Lamp should come on at 111^oc +/- 3,5^o on 143 ohms +/- 10%.

Inge K.

My sons 1985 k100rs runs great but will not start when hot. I don't mean over heating hot. Just if you ride it a while then shut it down it will not restart till almost cold. Which sensor would control that. Or is it a relay or somthing else I am missing.

I would rather guess it`s a temp. dependent open circuit (or short) that occurs.
To narrow it down a bit, have you checked if it got spark....does injectors click
....when this happens.

Inge K.

These bikes have an 'overheating' safety. When the sensor detects that the bike is too hot it'll allow it to run, but as soon as you stop it you'll have to wait until it has cooled down enough. This is controlled (AFAIK) in the ECU. Measuring between pins 10 and 13 on the connector (wire side) should tell you. A short here (between the sensor and ground) will give a similar behaviour. Have a look at Bert's splendid explanation on the home page.

+ 1

I'm doing some work on 3 different speedometers (85K). I want, the easiest way to verify that the temp light will illuminate should the relay tell it to.
I'm having a bit of difficulty reading the actual speedo cluster wiring dia. As I see it the temp warning light is on pin #10 and it grounds on pin #6. Anyone verify this?
Since I don't want to tear into the bike to get to the relay box or into the front to get to the fan wires. What's my easiest way to test the temp light circuit through the instrument cluster.
I'll assume If I can make it work on the bench, that it will work when required. Since I've never seen it on my every day speedo, I'd like to wire up a bulb check on that one also, before I reinstall either or both on the bike.
Also, can I test the bulb function on the fuel light(s) on the bench?
On my everyday speedo, I have installed a fuel light board that runs both lights 7 & 4.
On the #2 speedo, I have installed a service bulletin advised board that is the update for the 7L light only...(or is it the other way around?)
Anyway, I want to test each on the bench if possible.
Tested & verified, both temp lights work correctly. Connected a 9V batter between #6 & #10