BMW K bikes (Bricks)

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pond snail

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Hello all,

K75 is very nearly back on the road, but I have an issue with the cooling fan operation.

I know it will not come on automatically, as have run the engine on idle, till the old radiator, which was pretty shaky, decided to leak in several places, engine hot!, and no fan coming on....

So, I have tested the system the best I can, the wiring checks out fine, no breaks or bad connections.

On the temperature relay, if I jump A2 to 45, the fan will run, if I earth pin A3, the overtemp warning light illuminates, but earthing pin E and nothing!, no voltage at pin A2.

The Clymer manual says to test the temperature sender by disconnecting the plug and jumping the two terminals together, with the ignition on, the fan should run, but I get nothing.

I have checked the wiring, from the temperature relay, the fan motor and the temperature sender, all seem fine, no breaks, continuity from one end to the other.

Is the Clymer test for the temperature sender correct?, I disconnected the female connector and bridged the two terminals with a piece of copper wire, with the ignition switched on, nothing happened.

Could it be a faulty temperature sender?, or should I be looking elsewhere?, forgot to say I have a brand new temperature relay, plus two second-hand ones.

Thanks in advance,

John

    

Inge K.

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The control circuit in the fan relay is powered by the FI relay....
so it's only getting power when you push the starter button, or the engine is running.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

pond snail

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Thank you Inge, so the tests I did on the temperature relay need the engine running?, is there a way to test the cooling fan circuit with the engine off?.

Could I perhaps disconnect the starter motor and keep the starter button pressed in?, would this cause damage to the ignition/coild perhaps?,

John

    

Inge K.

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Or carry out a bench test....Power to terminal 9, ground to terminal 31.
When you ground terminal E, the relay should click.

But just for a test your metod with a disconnected starter seems easier.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

pond snail

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Thats great, thank you Inge, will do that tomorrow.

Do you know a test for the temperature sender, preferably with out removing it from the machine!..

John Very Happy



Last edited by pond snail on Sat Apr 15, 2017 8:52 pm; edited 1 time in total (Reason for editing : Spelling....)

    

Inge K.

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pond snail wrote:Do you know a test for the temperature sender, preferably with out removing it form the machine!..

Measure the resistance between terminal E and 31 in the relay socket.
Compare with the temperature diagramme in the troubleshooting guide at the portal.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

pond snail

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Thank you Inge,

Shall do the tests tomorrow, and report back,

John Very Happy

    

Inge K.

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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

pond snail

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Hello, a quick update,

Seems my temperature relay is OK, I performed the following bench tests,

With the relay removed from the harness, I put power + to pins 9 and 45, and earth/ground - to pin 31, then with a digital multimeter connected to pins A2 and 31, I earthed/grounded pin E, at which point the voltage meter read 12 volts, the relay is working OK.

Another test with the relay removed from the loom, I put power + to pin 9, and earth/ground to pin 31, then by earthing/grounding pin E the relay makes an audible click, the relay is working OK.

The other test I performed was with the relay fitted back to the loom, with the ignition on and pin E earthed/grounded, I pressed the starter motor and spun the engine over, as soon as I released the starter button, the fan came on briefly, the relay is working OK.

I assume the delay in the fan starting when the starter button was pressed is due to the load shed relay?, then shortly after the button is released, then the circuit is de energised?, hence the fan only running briefly, the ignition was still on after the starter button was released.

So, the temperature relay seems fine, the wiring seems fine, the next thing to look at is the temperature sender itself, I tried the test recommended in the Clymer manual, removed the sender plug/socket/connector and jumped the two terminals in the connector together, nothing happened, tried with the ignition on and pressed the starter button, but nothing.

I have resistance from the sender, measured through the loom, forget what it was, will test again, measuring the resistance between pin E and pin 31 at the temperature relay and make a note of the reading this time...

A question, is the Clymer method of testing the temperature sender valid?, by simply jumping the two terminals of the sender connector, removed from the sender, should the fan run?.

Also, the values given in the temperature diagram in the troubleshooting guide at the portal on this site, is there much leeway to the readings obtained from the temperature sender itself?, where the sender will no longer function?.

Thanks to Inge and Bert for setting me on the right path, very much appreciated,

John Very Happy

    

Inge K.

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pond snail wrote:
A question, is the Clymer method of testing the temperature sender valid?, by simply jumping the two terminals of the sender connector, removed from the sender, should the fan run?.

I think this test is for the 4V models which have a different sensor that isn't connected to ground...the signal is just passing through the resistor.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Peterk100rs

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Had same problem on my k100rs . Did the test jumping the connector from temp sensor and fan didn't run. I had to lift tank and trace fan cable up to connector top left of frame under tank . Theres a connector here you can take off and connect the fan directly to the battery . Fan ran straight away.
I got a new temp sensor and connected it up and still nothing . Checked the relay and power to it and all was as manual . I needed up putting a manual switch on the middle console for the fan ,which I put on when I come into traffic.
Not the answer your looking for but may save you you some time

    

SniperX

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Mine was a right doddle to diagnose. I removed enough of the fairing to get access to the fan and tried to spin the blades. I had to put enough pressure on the blade to almost break one off! I ordered a new fan....


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1972 BMW 3.0CSL, 1985 BMW Dinan 535i, 2001 Honda XR400R (plated), 1985 K100RT, 2004 ZX3 Focus, 1991 Dodge Power Wagon 4x4. 1977 Plymouth Trailduster 35K original miles!
    

Flip2

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B@pondsnail - when you tested your relay back in the loom , by earthing Pin E and pressing starter, can you explain how you did that, as I'm still learning. So far I've done a couple of the bench tests with the relay out of the loom and it appears my NEW temperature relay might be shot .

    

charlie99

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don't forget they have 2 power feeds


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

SniperX

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Can I just test it out of situ bu using a VOM, and testing for a closure when I get the temp sensor to say 180 or more degrees F in a pan of hot water?


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1972 BMW 3.0CSL, 1985 BMW Dinan 535i, 2001 Honda XR400R (plated), 1985 K100RT, 2004 ZX3 Focus, 1991 Dodge Power Wagon 4x4. 1977 Plymouth Trailduster 35K original miles!
    

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