K100 fan starts at 90 degrees.

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switchback
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K100 fan starts at 90 degrees.

Postby switchback » Mon Sep 06, 2021 5:44 pm

I have a K100 engine fitted in a Grinnall Scorpion. The cooling fan has started switching on at around 90 degrees rather than the correct 104 degrees(or there about) that it used to come on at. At first I changed the temperature sensor with no change, I then changed the temperature control switch/relay and still no change. I'm sure that the gauge is reading correctly as you tend to get a feel as to when the fan should run based of previous experience. I've also checked and cleaned the earth points. Any ideas what else to look at?

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MikeB
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Re: K100 fan starts at 90 degrees.

Postby MikeB » Mon Sep 06, 2021 8:30 pm

Hi,
The issue that you are experiencing sounds remarkably similar to the problem I am having with my bike - see postings recently on the forum.
I have changed various parts as you have done and I was also able to borrow a Motronic unit, all with no effect on the issue.
My next line of enquiry will include really good cleaning and flushing of the cooling system because I just wonder if it is possible for some muck to find its way to the area around the coolant sensor (below the radiator) so preventing the coolant actually getting to the sensor so causing it to only detect the heat of the castings?
Good luck
Mike
BMW R100RS Motorsport, BMW K1, BMW1100S, BMW R1200GS

switchback
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Posts: 9
Joined: Sat Apr 01, 2017 4:47 pm
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Location: Beccles Suffolk

Re: K100 fan starts at 90 degrees.

Postby switchback » Sun Sep 12, 2021 5:46 pm

Mine is definitely clean and filled "water solid". I checked it as I had the same thoughts as you. On the Scorpion the filler cap is just above the stub pipe where the sensor is fitted so it's easy to check.


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