now my temp gauge is frozen!

[FiveSpeedSquirrel]

I posted a couple of times about my 325i running with the temp gauge not fully warm. The gauge has always demonstrated a normal, gradual increase in temperature as the car warmed up, it just didn't show the temp as high as it should have.

Well, tonight it has basically frozen with the needle right on the blue part of the gauge. It doesn't matter if I'm idling or flying down the highway. And it sat for like an hour, I started it up and it was right back on the blue.

The gauge does flicker back to its resting position, all the way to the left, when I turn the car off.

Now I think the problem is electrical instead of mechanical. I think it may be the temperature sending unit, rather than my thermostat. The car had enough coolant the last time I checked it, I will check again in the morning.

Any ideas? Suggestions? Ways to check the temp sending unit?

**On a lighter note, I did buy "101 Performance Projects for Your 3-series" tonight :D

[R4g3fist]

You can pull the temp sending unit and do the old ohm meter trick across its contacts. Take it out cold, use a heat gun or hairdryer or hot water to dunk it in and see if it changes resistance the way it is supposed to. I don't know the values offhand, but I'm guessing that if it does it at all it will most likely not be faulty.

How cold is it there? On a really cold day around here, if I drive at highway speeds and don't really crack it (60's or so) the temp reading will climb way back down into the blue. It is a little weird that at idle it isn't rising at least to 1/4 hash.

Also, tap the plastic in front of the gauge and see if it changes position / reads higher. I had my fuel gauge go, and it wouldn't read at all unless I technical tapped the plastic a time or two. Made me feel like I needed to turn my car over to Xhibit to get pimped . . .

[FiveSpeedSquirrel]

I did try tapping on the plastic, no changes. And after about an hour of driving on two separate trips tonight, it hasn't moved. It was even idling while I was in Brnes and Noble for a few minutes, still no movement (my girlfriend watched it for me).

[jlevie]

A quick check is to short the contacts at the sensor end of the cable. That should drive the needle to full hot. If that works the sensor may be open (check with an ohmmeter).

A bad SI board/batteries or poor contact where the temp gauge mounts to the main PCB in the cluster is another cause of abnormal behavior of the temp gauge. The test above should help determine if the problem lies in the cluster.

[FiveSpeedSquirrel]

PROBLEM FIXED... I replaced the temperature sending unit and now all is well. The temperature fluctuates along with my driving, and always hovers between the 2nd hashmark and the middle hasmark.

Oh and I bled the system of air bubbles also.