Ok gang, here we go....

Last year on a return from Europe, got stuck in the mother of all jams on the M25, very hot day and very hot bike.  Cooled down to normal temps when moving but no fan cutting in.  Now since I've laid the bike up for winter and got on with some update/improvements, I've replaced the fan motor (bearings seized) from euromotoelectics for £53 inc. (postage from USA). reinstalled fan/radiator and fresh coolant.
Started bike up and waited for it to cut in - nope.
Removed Temp relay and linked 15 to A2 and fan works fine.
Checked resistance at sensor engine luke warm, 4600 ohms.
removed relay cover, no signs of dry soldering or burning, plugged back into socket and with ignition on moved the solenoid by hand, fan cuts in ok.
Checked continuity of all wires and appear good.

Here' the cunundrum, do I need to replace both the relay and the sensor, or is there a way to test the relay on it's own???

I have sourced a new sensor using the original BMW part number from World Car Parts for £12.50 inc. postage (much cheaper than other suppliers we could name...) and awaiting its arrival.  When it arrives I shall fit it and try again!

In the meantime, if anyone has any ideas?  P.S. Fuse is OK.

 

Cleverbee wrote:
Checked resistance at sensor engine luke warm, 4600 ohms.

4600 ohm would correspond to approx. 8 degrees celsius,
it seems like you got a problem With the sensor, related wiring or connectors.


The fan should kick in at 103 ^oC ~ 175 ohms.

Thanks Inge K,

As I said, apart from replacing all parts, I'm at a loss, wiring/fuse ok, so I'm starting with the cheapest option of the sensor.

Searched many sites for testing the Temperature Relay, but no joy.

Will see what the new sensor does

New info added to my previous post.

You can check the relay by grounding the sensor wire, disconnect the
injection ECU first.....(both sensor wires have the same colour code)

The relay gets the power from the FI relay, so the engine must be running.
The relay needs to be tested out of the bike.

Or find the correct wire of the two at the sensor (or the one at the relay
socket) and ground it temporary when engine is running.

About measuring the sensor: it's a dual element, you must measure
between each of the two connectors and ground (housing).
It also have been some who have found a bad connection between the
sensor housing and the water stub.

Had a similar problem. On advice from those who know more than me, I pulled the sensor out and gave it a good clean. Seems there was corrosion around the sensor end and metal stub pipe so a good clean up was all that was needed, the sensor worked perfectly out of the engine.
Here's a tip, drain the coolant before you pull that sucker out. How do I know?..... 

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When you say started bike and waited for fan to cut in, how long did you wait?

Some here have almost gone to work for the day then come home after 8 hours to find the fan just kicking in.

If you can ride the bike, take it out for twenty minutes then come home and let it sit.
Give it a good twenty to thirty minutes. They don't get that hot just sitting. Get the engine, gearbox warm first.

A remote possibility might be the relay's internals.  I had a fan problem on my other K100RS and it turned out that soldering on the circuit card inside the relay case had fractured.  This caused an open circuit in the connection between the main board and the daughter card.  I applied a bit of judicious heat to the fracture, which melted the solder and repaired the connection.  Things worked after that.

I suggest that you inspect the circuit card in the temperature relay, if you feel up to the task.

Hi, I need to replace temp sensor also and am intrsted in how u get on with WCP sensor...

Cleverbee wrote:I have sourced a new sensor using the original BMW part number from World Car Parts for £12.50 inc. postage (much cheaper than other suppliers we could name...) and awaiting its arrival.  When it arrives I shall fit it and try again!

Well new sensor arrived today AND you can remove it without having to take the radiator out!!!  Used a long 19mm socket and lost about 10cc of coolant max!

I'm not in a position to take the bike out on the road, so I started it up again in the garage and watched the temp gauge rise back into the red - no fan....?

I have got an infra red thermometer and depending where I pointed it I got different temperatures, 225 at the base of the radiator, 210 at the junction where the sensor is.

Call me chicken, but don't want to unduly cook the engine for the sake of trying the fan to cut in.

Will try out on the road when the rest of the winter jobs have been done on it  

Your old sensor was far from correct, so it was no loss to get a new one.
You did measure between ground (housing) and each of the connectors?

You could also check the relay out of the bike....terminal 9 = 12V+, 31 = 12V -
when you ground terminal E you should hear/feel that the contacts closing.

And the radiator cap will blow before engine damage is done.