K1 cooling fan again

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MikeB
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K1 cooling fan again

Postby MikeB » Sun Jun 20, 2021 12:55 pm

I know that the K bikes run hot and that the problem can be worse with the enclosed K1 but surely my cooling fan shouldn’t switch itself on just as the temperature gauge moves a quarter way off cold and then stay on for as long as I ride the bike? The fan never switches off and only does so when I stop the engine and remove the ignition key - it does not switch itself on and off when it is needed and for example yesterday morning when it was cool, coming back into my home town after a short ride at normal traffic speeds the fan was still on constantly.
To try and chase this gremlin out of my bike I have flushed the cooling system through, replaced the sender under the water/oil pump for the gauge as well as the coolant sensor behind the radiator which switches the fan on and off and talks to the Motronic box and yet the problem persists.
The warm air blown out of the side vents after a run isn’t anything more than warm suggesting that the temperature gauge is correct but the fan continues to spin constantly. I should add that the overheat light doesn’t glow except for when I first turn the key. I should also add that the ducting around the engine behind the radiator is all carefully fitted with no gaps.
Could this be a symptom of the fan relay playing-up or do I need to start thinking about replacing the thermostat? Or are there any other sensors that I need to be looking at?
As usual I will be grateful for any advice or suggestions.
Take care
Mike
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Re: K1 cooling fan again

Postby DEEP DIVER » Sun Jun 20, 2021 1:03 pm

To check the relay try swapping it with a light relay if they are the same.
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Re: K1 cooling fan again

Postby MikeB » Mon Jun 21, 2021 6:37 pm

Hi Deep Diver,

Thank you very much for your advice. I will give it a go next time I get some garage time.

Can anybody tell me, do all K bikes run their fans constantly?
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Re: K1 cooling fan again

Postby george baker » Mon Jun 21, 2021 7:32 pm

Hi
my K75 does'nt, in fact I'm not sure I have heard it run

George
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Re: K1 cooling fan again

Postby MikeB » Mon Jun 21, 2021 8:02 pm

Thanks George,
That’s interesting to know. I can’t imagine that BMW developed a bike that should have its cooling fan constantly running so I am sure that something isn’t right.
I wonder if there is something in the Motronic unit causing it?
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Re: K1 cooling fan again

Postby keiththeoutfitter1 » Mon Jun 21, 2021 9:55 pm

Is there possibly an airlock in the system which is leading to a hot spot around the fan temperature sensor? I know that when I change the coolant on my K1100 I have to ‘burp’ the system by squeezing all of the rubber coolant hoses to get the air out of the system.
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DEEP DIVER
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Re: K1 cooling fan again

Postby DEEP DIVER » Mon Jun 21, 2021 10:32 pm

Is there possibly an airlock in the system which is leading to a hot spot around the fan temperature sensor? I know that when I change the coolant on my K1100 I have to ‘burp’ the system by squeezing all of the rubber coolant hoses to get the air out of the system.
Plus 1 on that. I had the same on a car I had years ago.
I tried to be normal once, worst two minutes of my life.
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Barry the old goat!!!!
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And a VW trike so I don't fall off :shock:

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Re: K1 cooling fan again

Postby MikeB » Tue Jun 22, 2021 6:40 am

Very good point!
The cast tunnel in which the sensor sits could easily trap air so I will give the plumbing a good squeeze whilst leaning the bike to the right.
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Re: K1 cooling fan again

Postby paul kent » Mon Jul 19, 2021 6:53 am

sounds like the thermo/time/temp switch is at fault here, its coming on at too low a temprature and therefore not switching off once its cooled down. Im not sure of its location on this bike, but commonly found on the side of the radiator or sometimes within a hose. anyway that wouold be the first thing i would change, also easy to test and see at that temp it switches on and off.
if that proves to be working correctly and within tolerences, you might then have a look at the water pump impellor or see if the rad is semi blocked and not allowing the coolant to flow through.
Have fun.

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Re: K1 cooling fan again

Postby Mike D » Mon Jul 19, 2021 9:38 am

I emailed Mike the following, but post it here for everyone to see:

Thermostat Opens @ 85C
Fan Switches 'On' at 105C. Fan relay triggered by an earth on relay pin 85 supplied by the Motronic (Pin 16 K Bikes to 1993 or Pin 2 K Bike from 1994).
Overheat light 'On' 115C
Rad Cap Blows at 120C

Mike

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Re: K1 cooling fan again

Postby Jaythro » Tue Jul 20, 2021 2:10 pm

A couple of things that I would like to add as K fans are notorious for not coming on until its very hot

Did you change Coolant and put water in?? If so get it drained and replace with Coolant STAT "but" make sure and burp it and make sure you have enough in the expansion tank to replenish it of there is an air bubble K head gaskets have VERY small bleed holes in them!

Water is not the best medium for heat transfer and also there are lubricants and anti corrosive additives in coolant!

Could the thermostat be stuck?

Could the Temperature gauge connection be corroded ?

IS the water pump impeller turning with the motor

There is not much we can see for live data with Diagnostics with these older systems But an INfra red heat scope may show if you have blockages in the radiator by showing hot and cold spots

And similar with the head and block
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Re: K1 cooling fan again

Postby John Marshall » Tue Jul 20, 2021 2:42 pm

I seem to think you could trigger a fan on a K75 at least by jumping A2 and 15 on the relay but my memory might be on the blink.
I do know what boiling coolant feels like when it ejects all down the top of your leg though after a cap seal failure.
A long time ago now.....
John

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Re: K1 cooling fan again

Postby george baker » Tue Jul 20, 2021 7:43 pm

Hi
the bond bug was known for getting gunk blocking the waterways, Calgun? a dish washer tablet was the recommended cure

George
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Re: K1 cooling fan again

Postby MikeB » Tue Jul 20, 2021 9:06 pm

Thank you all for your advice and suggestions.
The problem is more one of the cooling fan running when it is not required and once it starts it does not stop.
I have rebuilt the oil/water pump and fitted a new temperature gauge sensor in the pump casting. I have also fitted a new engine coolant temperature sensor that I have tested at the Motronic plug and found that it does reduce resistance as the temperature rises: at 21C it’s 2.25K ohms, after a short run and at the point the fan cuts in it’s 0.016K ohms. The temperature gauge at the point the fan cuts in is just about a third of the way around the gauge so a long way from the red sector and I should add that the temperature warning light does not illuminate.
I have flushed the radiator with Holts cleaner and replaced the thermostat. I have also burped the system but I agree that there could be air still trapped somewhere, but where?
Mike D has also been extremely helpful in investigating potential electrical/Motronic problems and following Rob’s suggestion I hired the club’s GS-911 which confirmed that that the fan works as it should and I cleared all faults that may have been logged, but the fan continues to start at a point before I think that the engine is properly warm, and it continues to run.
Mike D has suggested that the new engine/coolant sensor is dropping resistance too quickly which causes the Motronic to switch on the fan, which sounds very plausible and so needs more investigation, preferably out of the bike in a pan of hot water.
Has anybody else experienced anything like this? Is it worth simply buying and fitting another new sensor, and apologies for being really cheeky, but has anybody got a spare good Motronic unit that I could borrow and plug in to determine if the fault is with my unit?
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Re: K1 cooling fan again

Postby MikeB » Mon Jul 26, 2021 7:12 pm

Just a quick update.
I managed to borrow another Motronic unit and it made no difference whatsoever.
That’s one potential cause eliminated and so the investigation continues.
Stay safe all
Mike
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Re: K1 cooling fan again

Postby Jaythro » Tue Jul 27, 2021 9:05 am

The one at the Pump is just for the Gauge

There is a second coolant temp sensor for the ECU on the stand pipe behind the radiator that is what controls the Fan

If you are getting replacement sensors I strongly suggest you get ones from BMW and then you know they are in spec

I have stopped buying certain seals from Outside suppliers as they are not OE too hard (not supple) and basically crap to install and have failed within a year

Also it may be worth checking/replacing your cooling fan relay IT may be latching too soon but could also be burned contacts not letting it unlatch

If you have assistance laying the bike as far over as you can on its cylinder head side with it idling will very much clear any bubbles But Kill the motor before you try and lift it everyone does the same thing and revs the gnarlies off it lifting them back up
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Re: K1 cooling fan again

Postby Mike D » Tue Jul 27, 2021 9:58 am

Hi Jay,

Ref: There is a second coolant temp sensor for the ECU on the stand pipe behind the radiator that is what controls the Fan

I was reading some notes from the BMW training school about the water/oil temperature sensor.

It states that the K series sensor used on the Motronic systems only has one NTC resistor element whereas the sensor used on the Jetronic models has two. It shows the Motronic sensor performing both the control of the radiator fan and the temperature light in the cluster. This is as well as the injector timing signal for calculation of the fuel enrichment for cold starting.

Is your comment about the second temperature sensor only applicable to the Jetronic equipped bikes (The OP has a K1 which will be Motronic M2.1?)

Mike

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Re: K1 cooling fan again

Postby MikeB » Tue Jul 27, 2021 6:05 pm

Thank you Jay, Mike,

I have replaced the fan relay a few weeks ago just in case it was sticking but apparently it wasn’t.

The new temperature sensor that I fitted into the ‘standpipe’ behind the radiator was bought from a very reputable organisation however it is not marked with any branding, so I have just obtained a genuine BMW sensor manufactured by Bosch which I am quietly optimistic will make a difference.

I will update when I get an opportunity to fit the Bosch sensor.

Stay safe

Mike
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Re: K1 cooling fan again

Postby MikeB » Sun Aug 01, 2021 9:27 am

A further update......
I replaced the coolant sensor (behind the radiator) with the new BMW Bosch sensor and it has made a small difference.
It now takes longer for the fan to cut-in but then it still runs continuously despite the temperature gauge dropping to the quarter point above cold.
The other difference is that when I switch the engine off and them immediately back on the fan stays off. With the previous sensor it would run after switching back on after stopping the engine.
The investigation continues but I am going to ride the bike for a few miles (whenever it stops raining) to see if by some miracle, the problem goes away.

Stay safe all!

Mike
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Re: K1 cooling fan again

Postby george baker » Sun Aug 01, 2021 7:22 pm

Hi
how about a switch in the fan line, ride the bike until the fan comes on, keep the engine on, flick the switch to turn the fan off when the gauge drops to 1/4, wait a couple of minutes and then turn it on again? If the fan stays off until the gauge rises again you know it is the off portion that is the problem.



George
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Re: K1 cooling fan again

Postby MikeB » Mon Aug 02, 2021 8:44 pm

Hi George,

That’s a very interesting idea thank you.
I really don’t want to cut into the loom but if I can find a matching plug and socket for the fan it’s certainly worth a try.

Take care
Mike
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Re: K1 cooling fan again

Postby george baker » Tue Aug 03, 2021 12:56 pm

Hi
Mike what is the connector like? I have lots of bits off a dead K11 so will look, if I knew what I was looking for AND, YOU NAG UNTIL I DO IT, cos I will forget (I forget almost everything these days)

George
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Re: K1 cooling fan again

Postby MikeB » Tue Aug 03, 2021 7:41 pm

Hi George,
Thank you, that really is very kind of you.
As soon as I get back into the garage I will take the tank off and take a picture. I’ll post it on this thread.
BTW, I forget everything too, I am a real airhead you could say!

Mike
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Re: K1 cooling fan again

Postby george baker » Tue Aug 03, 2021 10:21 pm

Hi
Nag me until I look, even daily PMs, I wont mind

George
Member 21, R100R, and an under used K75


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