My bike is K100RS '87 it is L-jetronic

Ned wrote:

BMW and others have things like that ... you can even get them on e-bay cheaply, but, i know, that this is not as much fun as building one. look for a diagnistic electronic tools ... I forget the actual name.

You mean GS-911?
It's not suit to K100RS

Yes, like that, but L-Jet has no CPU so no error codes.

One can make a nice unit to readout all the critical values for diagnostic purposes (dynamically), but again, our bikes are not going to last forever and the market place is limited if you are thinking about marketing.

Guys, and who's got ideas for a case of temp light on after a few minutes normal ride and fan working?

Temperature going up fast hence pump not working fine?

PS love this thread title, I feel it!

Possibly the thermostat isn't opening and so the coolant is just circulating through the bypass and not the radiator.

RicK G wrote:Possibly the thermostat isn't opening and so the coolant is just circulating through the bypass and not the radiator.

Thank you Rick, I'm going to to run a drain/flush this morning because there might be air and then I'll give the thermostat a check.

I have drained and flushed the coolant/water cocktail but nothing changed.

Here's the situation:
Cold engine starts and idling > 5' later the fan starts (while gauge indicates just past the blue bars of cold temp) > a few seconds and red temp light comes up.

I've noticed that in the compensation tank the water is cold, could this all be explained by a faulty thermostat?

PS The gauge wrong read could be because it's listening to a part of the cooling system where there is no hot water running.

I would be looking at the thermostat next.
Place the thermostat in a saucepan of water and boil the water, the thermostat should open before the water boils and be fully open when the water boils. You can raise the boiling point of the water by adding salt if needed.
If it has not opened by the time the water has boiled then it is frittzed.

Just boiled the thermostat and it opens (stretches out) fine, I assume it's working so now I'm very puzzled on what's the problem with my cooling system. Should I start a new thread maybe?

I notice it's a 1986 model. Did you check the water pump? If it has the original impeller shaft with a nut holding the impeller to it, then it may have sheared off. Easy to check by removing the plate from the front of the pump.

Avenger GT wrote:I notice it's a 1986 model. Did you check the water pump? If it has the original impeller shaft with a nut holding the impeller to it, then it may have sheared off. Easy to check by removing the plate from the front of the pump.

I had to open to plate to get the sensor wiring through, it had lots of dirt like minuscole grovel (mineral from tap water someone used before me?) that I tried to clean away.

I haven't touched the impeller at all and it worked fine until I've done this auxiliary instruments job.

Here's what I've found once removed the lid a couple of weeks ago:

sobonatovada wrote:I haven't touched the impeller at all and it worked fine until I've done this auxiliary instruments job.

If the cooling system did funtion as normal until you drained and refill it,
I would guess that you had a airlock in the system.

Fill the system slowly and when it almost full, squeese the hoses several
times to get all air out before topping up.

Another thought too: that's the very early type cast steel impeller. If it's anything like mine was, the bit you can't see is now a solid mass of rust that will be just rotating in the coolant rather than actually circulating it. Motorworks will sell you a secondhand later-type impeller for £4; ask them for the spacer too. Yours doesn't have one. The later impeller is literally a bolt-on fit. My guess is that the nut-shearing problem was caused by the sheer mass of the early impeller.

What you now need to establish is, is the coolant actually circulating and is it actually getting hot or are the sensors faulty.
The thermostat should block the coolant path through the bypass when it opens.
I spent a few hours trying to find a problem of overheating (not a K) when the sender was at fault and making me think it was really hot when it was barely past normal.

Before facing the music of a pump rebuild I tried once again to drain/flush and pump air out, then added coolant and water (for a total of about 3 liters) and it seems it's working fine now 

Let the engine run for minutes on idle, fan started, no light on dashboard flashed, have then ran for 10/15 mins in the city and still no light came up

Thank you everyone!

PS Although I've noticed the auxiliry instruments for the water temp is at about 1/3 when engine is hot (say after 10/15 mins, air temperature today was 32C) and that's strange, I would expect it at half scale, vertical, upright, in normal running situation, anyone has it on their K100RS and can confirm/report? Thanks

Dai wrote:Another thought too: that's the very early type cast steel impeller. If it's anything like mine was, the bit you can't see is now a solid mass of rust that will be just rotating in the coolant rather than actually circulating it. Motorworks will sell you a secondhand later-type impeller for £4; ask them for the spacer too. Yours doesn't have one. The later impeller is literally a bolt-on fit. My guess is that the nut-shearing problem was caused by the sheer mass of the early impeller.

The shearing problem has nothing to do with the mass of the impeller, the shaft is poorly designed (weak). 

Sobonatovada, don't even think of removing that impeller until you absolutely have to. The end will probably break off the shaft if you do. Good that you have sorted the problem. You have to pour the coolant in slowly and make sure that you get all the air out.

Inge K. wrote:

sobonatovada wrote:I haven't touched the impeller at all and it worked fine until I've done this auxiliary instruments job.

If the cooling system did funtion as normal until you drained and refill it,
I would guess that you had a airlock in the system.

Fill the system slowly and when it almost full, squeese the hoses several
times to get all air out before topping up.

or fill it whilst on the side stand ...then leave it for a 1/2 hour for the bubbles to rise to the filler neck ?

just an observation

good to hear its working again ...

cheers

charlie99 wrote:good to hear its working again ...cheers

+1.

those **** connectors!...
having recently worked on a korean motor with lots of this type of connector I eventually sussed that by pressing on the wire clip the connector will separate so removing the clip isn't necessary with most of them...

Crazy Frog wrote: There is a wire clip around. You have to get a very small screw driver and slide it under the wire. You then spread the clip apart. This is the same type of clips that you find on the injectors or the idle switch. Better to try removing the clip on the idle switch to see how it works. At least it's accessible. The temperature sensor is difficult to access and if you haven't seen these clips you could work for hours before taking it off.