I'm new to the forum and I hope to be able to provide input to questions posed by others as well as getting some help when I need it.

Today's issue is that my '87 K100RT is not reaching normal operating temperature. The 85°C thermostat appears to be working (it opens in very hot water and closes when the water is less than 160°). The temperature gauge appears to be functioning correctly and when I let the bike idle long enough, the fan comes on when the engine temperature reaches 190°. Under normal driving - even in stop and go - the temperature does not climb above 170° - usually a bit less. Ideas?

Hi welcome to the forum.
The fan should come on at 103°C or 215°F so if your gauge is reading 190°F at the time the fan comes on then I would be looking at the gauge or sender.  If you know the fan will turn on and it's running fine I would be inclined to leave well alone and accept that the normal running conditions show a little different on your bike.

The relationship between the normal temperature and the higher temperature for the fan cut in look ok to me and suggest that the thermostat is doing its job and the fan/sender is also doing its job.

Suspect the gauge reading, sender or connections to it. But not sure I would lose sleep on it as lots of Ks have no gauge and only the high temperature warning light. Do I correctly assume this is not coming on [I believe it would come on at a higher temperature than the fan cut in].

The light come on at 111°C.

Light on at 111C. 111C is 232F and that's a long way off 190F.

The fan on at 103C or 217F also is correct. Both of these are as given in Clymer manual.

You say the fan cuts in at 190F which is 88C. That's a long way off.

The thermostat is set to open at 85C [again correct] which means it should be open at 185F. But if the temperature is not going above 170C then the thermostat will not be opening very much. You are also saying it closes at 160F which is 71C. I am not sure if that is correct but it seems off and should be closing at a higher temperature.

You can make a simple check by starting from cold and seeing if the pipes to the radiator get warm quickly. If they do then it means the thermostat is opened. If your coolant level is correct and there are no leaks then all should be good.

Everything is still pointing to a problem with the gauges and a sensor or electrical connection I suspect could be the causes.

Is it possible there is a mismatch between the gauge and the sensors? Does the gauge display C or F? Also check that the radiator cap is good as it must form a seal to raise the pressure in the cooling system but I don't think it would cause this problem.

Question for Rick G /CF or someone with more knowledge on these things: I could ask do all these go through the ECU which if it were to malfunction would cause this problem?

I will check the temperature of the radiator hose a few minutes after start-up. This should give me the best indication if the thermostat is indeed opening too soon. Other than that, the advice to "leave it alone" is probably good advice given that the gauge and the fan appear to be working as designed.

The fact that the hose gets warm will tell you the thermostat has opened. There will be a time lag that means you should not rely too much on the temperature gauge. But you know the fan and thermostat are both working correctly which is the key.

I really suspect a problem with your temperature gauge and not the electronic of the bike.
If you want to have an accurate reading, use an Infrared thermometer pointed at the radiator.
They are cheap and you can use them for all kind of purpose: cooking the turkey, checking the cold spots in your house (to see where extra insulation is needed),.... If you tell your wife that this is the main purpose, she'll buy one for you

Crazy Frog wrote:I really suspect a problem with your temperature gauge and not the electronic of the bike.
If you want to have an accurate reading, use an Infrared thermometer pointed at the radiator.
They are cheap and you can use them for all kind of purpose: cooking the turkey, checking the cold spots in your house (to see where extra insulation is needed),.... If you tell your wife that this is the main purpose, she'll buy one for you

The real reason you are buying it is the property it has of recording temperature. Keep checking the house and also keep checking wife temperature. Watch the spikes and you will soon know when its not a good day to announce you are going for a round of golf with the lads...

92KK K100LT 193214 wrote:Light on at 111C. 111C is 232F and that's a long way off 190F.

The fan on at 103C or 217F also is correct. Both of these are as given in Clymer manual.

You say the fan cuts in at 190F which is 88C. That's a long way off.

The thermostat is set to open at 85C [again correct] which means it should be open at 185F. But if the temperature is not going above 170C then the thermostat will not be opening very much. You are also saying it closes at 160F which is 71C. I am not sure if that is correct but it seems off and should be closing at a higher temperature.

You can make a simple check by starting from cold and seeing if the pipes to the radiator get warm quickly. If they do then it means the thermostat is opened. If your coolant level is correct and there are no leaks then all should be good.

Everything is still pointing to a problem with the gauges and a sensor or electrical connection I suspect could be the causes.

Is it possible there is a mismatch between the gauge and the sensors? Does the gauge display C or F? Also check that the radiator cap is good as it must form a seal to raise the pressure in the cooling system but I don't think it would cause this problem.

Question for Rick G /CF or someone with more knowledge on these things: I could ask do all these go through the ECU which if it were to malfunction would cause this problem?

The fan comes on through the temp sensing relay and does not go through the ECU but the light does work through the ECU and works from the same side of the sensor that the ECU gets it's temp reading for mixture.

That points to the sensor or the gauge IMO.

I would be checking the gauge first. If as you say 92 the sensor has been replaced with a different brand then it would or could do that.
Now that you mention it I seem to recall someone saying that there is a VDO sensor will go into the same hole but doesnt read the same and as usual I cant find the thread.

Rick

I guess the important thing is that mechanically all seems ok to ride. You are right about the VDO sensor issue, I remember that too but not looked for it. I have been happy enough to have just the warning light.

Olaf.

yep the sensors for the guage are pretty specific ....and dont read correct on vdo and motometer (late release)....recent production runs

there was a different sensor way back ( like our k bikes .) but seems to be discontinued ?

i think i had to add 80 odd ohms to get my motormeter temp guage working close to correct with the bmw sensor

hope that helps

My water temp gauge stopped working. Where is the sensor located? There seems to be 4 wires going into the gauge.

Under the water pump, the lower nearer the ground is apparently for the gauge and the upper one for the warning light sensor. Bikes with no gauge have a drain plug at the lower sensor position.

The upper sensor is the oil pressure light.

Hi Dave,
Welcome to the site I suggest you post your question over in the technical section, not all of the gurus read the new members section and you may miss the opportunity of them giving you an answer.
Regards,
K-BIKE