Which temp sensor is which?

[Griffin]

Car is an 84 318i.

Its obvious to me that the one on the radiator is for the electric fan, but there are multiple other temp sensors in the coolant path. Which is which? One for ECU and one for gauge I presume, maybe even a separate one for a cold start circuit.

I'm battling an inoperative temp gauge (the needle moves a tiny bit when powered up, but no temp signal) as well as a permanent high idle condition which leads me to believe that the car thinks its always cold and in cold-start mode dumping excess fuel. I have Chiltons, but its got about 20 different cars and lacks pictures or descriptions that I need for this.

[Jean]

Have you seen this already ?

http://www.realoem.com/bmw/showparts.do?model=1074&mospid=47302&btnr=11_0683&hg=11&fg=35

If the temp gauge is acting up it could be many things, a loose nut on the back of the cluster holding the temp gauge for example. Bad solder joints on the main board in the cluster where the C1 and C2 (blue/white) connectors are.

You can try and disconnect the wire(s) from the sensor closest to the diagnostics port (to the right in the picture) and check the temp gauge. Also you can short the wires and see if the temp gauge moves or not...

[Dylboz]

Check your gauge cluster connections. Also, tighten the brass nut at the back of the temp gauge itself. Mine would jump around and then just fall to zero. I tightened up the brass nut (there's one on the fuel gauge too), and then I wedged the connectors (blue and white on the back of the cluster) tight with little shims, and I haven't had any issues since.

[Griffin]

I bought another cluster because my odometer didn't work and just plugged it in and went... the old gauge was bad as this one works. Before I swapped it out, I tried the jumper and no movement. Upon removing the old cluster the nut was still tight so I'm sure there was a more internal failure within the gauge. Thanks guys!