The coolant warning light and fan come on after about 1 minute running at idle from cold.

It's not heating up that quickly as it's still cool to touch when it comes on.

What could cause this? Is the fan and light triggered by the temp sensor?

Thanks

Probably your coolant temp sensor. Pull the temperature controller and measure the resistance across the socket pins #E and #31(earth). Should measure 2.5 kilohm but that fault would be reading somewhere less than 200 ohms.

Just checked sensor, it's reading about 3K on both terminals so can't be that.

Hello.
Some years ago i had the same problem in my k100rt. 
Have a look at my topic SHE GOES CRAZY on eletric problems i think, and check the ground points of the engine to the frame.
Good luck

Thanks some good info in that thread, will need to check my earths, there are no cables from battery to engine on mine.

hello
also check the bolts that old the frame to the engine, clean the surface and retight them.
my problem was just there.i hope you have the same,its very simple

let me know if you found it

don´t give up

good luck

half brick wrote:Thanks some good info in that thread, will need to check my earths, there are no cables from battery to engine on mine.

There must be an earth connect somewhere as the engine is running and lights are working. I'd say someone has connected the battery Neg straight to the earth connection under the tank. That's OK but I'd suggest installing the OEM earth cable from the Neg battery terminal to the gearbox also. There's a connection lug on the left side. This is important for the starter motor as it earths thru its mounting bolts to the top of the GB nearby. The starter motor armature and brushes need to be clean and in spec also to maintain a good earth connection thru the starter motor. 

Without the GB earth connected the starter earth has to find its way thru the engine mounting bolts to the frame and from there back to the battery Neg terminal and it draws a lot of current at startup. The GB earth connection is more efficient for this.

With both the frame and GB earths connected, you won't need to worry so much about getting connection thru the engine mounts. With the OEM earthing setup they are critical.

If the temp sensor checks out OK and there is nothing else 'weird' happening with instruments or running light then the warning light/fan issue may be a faulty temperature controller

Check the coolant pipes are getting hot. A wild thought is sheared off water pump impeller......

One thing to check is the relay.
My friend has a 94 k75 that had been stored and only done 18K, so virtually brand new. When we went on a ride the temp light would come on but not the fan and the temp gauge would be in the normal. This would happen intermittently.
We checked all connections, flushed fluid etc, and our local tech Genius Brian from Munich Motors told us it was the relay.
A quick swap and all was well.
It is very strange that it comes on after a min from cold, and the bike is still not warm, so that would suggest its not a mechanical issue.
Worth a try
Cheers
Mike

I made up an earth lead from the battery to gearbox point. I get a dead short from the sensor body to the battery so earth is good.

I ran it for about 10mins, all the hoses and radiator get hot so I think that means my water pump is OK? Coolant level is fine.

Tested the sensor after I shut it off and got 400ohms. 3000 when cold.

Will check the relay.

Relay appears fine, not stuck on or anything. Wires on it's plug all test fine going by this link - http://www.ibmwr.org/ktech/fan-diagnosis.shtml

Removed temp sensor and checked resistance at a few temperatures (in degrees Celsius):

18 degrees (ambient) - 2550 ohms

30 degrees - 1220 ohms

45 degrees - 700 ohms

70 degrees - 400 ohms

Do these readings seem normal?

half brick wrote:18 degrees (ambient) - 2550 ohms
30 degrees - 1220 ohms
45 degrees - 700 ohms
70 degrees - 400 ohms
Do these readings seem normal?

Here is what is expected. It seems that from 30 degrees to 45 degrees the reading is totally out the range. I believe that you are in need of a new temp sensor.

I think I  recall seeing a few of the  bulb monitoring units going faulty over the years
the reason was cracking of the soldered joints from the terminals to the  pcboard

I wonder if this could also be the case with your temperature relay unit ?

if the relay board lost connection somehow ....

it looks like an easy task to reflow the solder on the right angle joints ...or indeed notice any defects  if you open it up


heres what they look like inside



but from cfs  observation it looks like the temp sensor readings  has some good deviation from normal

That's how I fixed mine Charlie.

I had the top off relay, no visible damage and there's continuity where there should be.

Tried a brand new temp sensor today, no difference. With the sensor body at 21 degrees Celsius the fan came on, followed shortly by the light. The sensor body has a perfect earth.

half brick wrote:I had the top off relay, no visible damage and there's continuity where there should be.

Tried a brand new temp sensor today, no difference. With the sensor body at 21 degrees Celsius the fan came on, followed shortly by the light. The sensor body has a perfect earth.

You can find a used temperature relay on Fleebay and they are cheap.
See here

Got a second hand relay from Motorworks, that has sorted it.

Thanks for all replies.

good to hear you got it sorted

cheers