temp gauge issues

[schnell944]

Just noticed today that my temp gauge was at the 1/4 mark despite driving it for a while. It's usually dead center after the car's been warmed up. I found that if I turn the car off after it's warm then turn it back on again the needle goes to dead center then begins moving down to the 1/4 mark in increments over a few seconds. I'm guessing the gauge in the cluster itself needs to be replaced, but wanted to check here to see if there any other theories. The temp sensor itself is only a few months old and what wiring I can see at the sensor is good. Thanks!

[shogun]

Another possibility: a broken thermostat in open position. I had that once on my E36 M3. When driving it was at 1/4 mark, when in idle, at red light or traffic jam, it moved to the center.
Is the heater working normally?

[schnell944]

I thought about that possibility at first, but it’s not a case of the temp creeping back up to normal at idle, rather, the gauge seems to work correctly for a moment when I turn the car off and on again, then the needle drops back down to 1/4 regardless of whether I’m driving or idling. Also, the heater is working fine, throwing good heat.

[shogun]

check the sensor with a multimeter, there are 2 sensors or 3 (in case the car has EML)
from left to right
http://www.realoem.com/bmw/enUS/show...diagId=11_4616
14 Temperature sensor, water 13621709967 for cluster gauge sender
16 Temperature sensor, water M14X1,5 12621288158 for EML
12 Engine coolant temp sensor 2-POL 12621710535 for DME

13621709967 gauge sender should be brown/violet-brown/yellow, sensor head is blue, at 20 deg. C is should have 2500 OHM
detailed list for that one is the first in this list at differemt temperatures http://www.e32-schrauber.de/bmw/s-tempsensor.htm

Also disconnect the connector and switch ignition on and see what happens at the temp gauge

[schnell944]

Thanks, shogun. Will check further next time I am able to take the car out.

[SergeBMW]

I had a similar effect when my thermostat was stuck open, 1/4 mark usually is where it settles when coolant is flowing full blast non stop. Also worth a check to make sure the needle is working properly. Perform a cluster test as well as the sensor check as stated by Shogun:

Cluster test:
Make sure the needle moves freely up and back down to the Blue side.
1.) With the ignition OFF, press and hold the 'Check Control' button (that's the stick-like button of the right side of the dashboard)

2.) While still holding the 'Check Control' button, turn the ignition to the ON position.

3.) Release the 'Check Control' button, the dashboard self-test testing program will execute displaying various informations...

[schnell944]

Thanks, Serge. Performed the cluster test, and the needle swept freely across the entire field. The only thing that makes me think it’s the gauge is that the needle will seem to “work” momentarily if I shut the car off and turn it back on when the engine is warm. The needle then quickly -in a few seconds- drops back from dead center to 1/4. Will check sensor resistance when I can take her out and warm her up again. According to PO records, the t-stat is way overdue so I plan to replace it soon anyway and have a new one ready to install. Thanks!

[schnell944]

Follow-up: Turns out the thermostat was split in half when I removed it! New t-stat was what it needed. Thanks!

[6erWEBB]

Whaaaaa!? Makes me think I need to break mine open. I’ve been putting that off cuz I can whack the dash and the needle goes to normal ha.

[shogun]

If you whack the dash and the needle moves to the correct position, that is a cluster problem, maybe the contacts, or ground problem...
That is a typical broken t-stat on the M70
6010205090_a9fcd48766_b.jpg