Author Topic: Some water temp sensor data points.  (Read 3517 times)

Offline frankenduck

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Some water temp sensor data points.
« on: May 15, 2011, 12:46:16 PM »
Local guy having issues with a K100RS4V:

- When hot, the bike stutters/floods past half throttle.

- Fan never comes on.

- Exhaust smells like fuel.

- Mileage has gone to crap.


I suspected that his temp sensor might be going.  Since I got that parts RS running (which I assume has a good temp sensor since it's only got 24k on it) and it uses the same water temp sensor I thought it might be interesting to compare the resistance at various temperatures.  I used the same BMW temp gauge on both bikes to remove any variance there.

Anyhow, it does look like he's got a bad temp sensor but I thought I'd document the readings I got at K11OG in case someone might find them useful.  Note that the 94+ bikes use a different temp sensor and Motronic so this data may only be applicable to 93 and earlier K1100s and K100RS4Vs.

In order to measure the resistance from the temp sensor for each bike I disassembled the Motronic connector so I could shove a multimeter probe in with the violet wire from the temp sensor.  (Note that when the bike is on the Motronic grounds it out so readings were taken by turning the bike off and measuring the resistance between ground and the violet wire.)

The "good" bike - 93 K1100RS:

More or less stone cold: 850 ohms

1/2 on the temp gauge(major hash mark to the left of the straight up one): 223 ohms

5/8(straight up): 178 ohms

3/4 (major hash mark to the right of the straight up one): fan kicks on at 143 ohms


The "bad" bike - 91 K100RS4V:

Didn't measure it cold since he rode it here.

1/2: 214 ohms

5/8: 197 ohms

7/8(start of red zone): 140 ohms and fan still hasn't kicked in


So it looks like his temp sensor is a wee bit off and fooling the Motronic into thinking the engine is colder than it really is and overfueling.  I'll update this thread once he's replaced the temp sensor.

(Disclaimer:  I wouldn't take the specific numbers as gospel but I think they're useful from an order of magnitude perspective.)
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