Temp Gauge not working properly.

[zeltax]

Hi guys,

I'm currently trying to sort out temp gauge issues in my 318i m40b10 1989.

Whenever the car starts and has been left on idle or I'm driving it, the temp gauge seems to sit just under the blue zone. For some reason, no matter how hot it is, the temp gauge doesn't move above the cold. See this video, https://www.youtube.com/watch?v=sJ5qamEwqFQ. It's what's happening to mine.

I replaced the temp sensor. The one I had in mine had corroded and it broke when I tried to remove it (see below) so I got a new one and got it plugged. A blue head plugs into this FYI.
20200206_133317.jpg
Checked the thermostat and that looked good too. Took out the instruments, cleaned and added contact spray and plugged it back but still seems to be doing the same. Fuses for AUX fan has been checked, as well as instruments and nothing seems to be out of the ordinary. Anyone got any ideas what I can do?

p.s my AUX fan for the AC doesn't turn on. When I jump the cables, it spins very fast, but pressing the AC button doesn't turn that fan on. Setting the speeds (1 2 3 or 4) doesn't turn on the fan either. Clutch fan runs fine. Not sure if it matters but whenever I press the AC button, I hear a click which is distinctive but doesn't seem to turn the aux fan on. I've put air con into it.

Thanks.

[superj]

temp gage could just be bad. maybe try swapping it with another person's to check?

the speeds, 1-4, is the fan blower resistor. its behind the little engine bay cover, on the firewall, if I remember right. it might also make your aux fan work when you change it but I am not 100% on that

[zeltax]

temp gage could just be bad. maybe try swapping it with another person's to check?

the speeds, 1-4, is the fan blower resistor. its behind the little engine bay cover, on the firewall, if I remember right. it might also make your aux fan work when you change it but I am not 100% on that

My blower resister is good. It works without an issue as I recently had taken it out to give it a clean. AC button also works when clicked. I have noticed however that when I jump my aux fan, it doesn't work for the low speed but only the high speed so most likely a aux fan resister failure. As for the temp gauge, it could be a bad gage.

If I haven't checked anything else, feel free to let me know.

[tomstin]

AC button also works when clicked.

On my 325, after the AC button, the circuit goes through a temp sensor in the evaporator that will shut the AC off if it freezes, mine was bad, ended up bypassing it. Then the circuit goes through to the aux fan.

[superj]

I was going to say I think it goes through some sensors in the ac system.

[Mikealwa]

Every drive my temp gauge stays below the blue until I hit the dash above the gauge. I have to do it every time. Worth a try!

[superj]

thats also true, ha ha ha. I have ot hit our 88 dash also to get the temp gage to move. I guess its just sticky from being so old

[agisthos]

After my E30 being off the road for many years I found the temp gauge not working, despite having replaced it with a new one. Sometimes it would flicker but mostly it was dead.

After doing a lot of reading up on the subject it seems to be instrument cluster related.

1. The pins on the temp gauge itself need to be sanded back to get better contact before being re-installed into the instrument cluster.
2. A ground point on the cluster PCB often needs to be re-soldered, as the temps sender relies heavily on the ground for proper functioning.

There are plenty of Youtube guides on how to remove the cluster and do these things.

I am just waiting on replacement Odometer gears, and will also then do the 2 things above.
I will report back if this fixed it.

[agisthos]

My temp gauge is now working. I'm not sure if it was point 1 or 2 above that fixed it, but one other thing I found when taking the gauge off the cluster PCB -the nut that contacts the ground point had a washer that was carbonized up real bad- so barely any current would travel from the gauge to the ground point.
Maybe just replacing the washer and tightening up the nut would have fixed it. I would add it to the list and do all 3 things as getting the cluster in and out is a PITA.

1. The pins on the temp gauge itself need to be sanded back to get better contact before being re-installed into the instrument cluster.
2. The temp gauge ground point on the cluster PCB (round hollow circle) often needs to be re-soldered, as the temps sender relies heavily on the ground for proper functioning
3. Replace the washers on both temp/fuel gauges, and tighten the nuts up real good.

[treff7]

It also wouldn't hurt once you're in there to replace the batteries on the SI board. I have a 1990 and I just replaced them. The temp gauge is one thing that acts funny when the batteries are on their last leg. Mine showed that the engine was overheating but it would randomly jump to the correct temperature for a second and go back up. I was getting ready to replace the thermostat when I saw the needle jumping around. After putting in new batteries i had no more issues.

[richardodn]

On my 325, after the AC button, the circuit goes through a temp sensor in the evaporator that will shut the AC off if it freezes, mine was bad, ended up bypassing it. Then the circuit goes through to the aux fan.

That's not correct. Turning on the AC switch provides power directly to the coil on the K1 normal (low) speed relay. The circuit branches to the AC components. To the OP, your diagnosis of the aux fan resistor is correct.

It also wouldn't hurt once you're in there to replace the batteries on the SI board. I have a 1990 and I just replaced them. The temp gauge is one thing that acts funny when the batteries are on their last leg. Mine showed that the engine was overheating but it would randomly jump to the correct temperature for a second and go back up. I was getting ready to replace the thermostat when I saw the needle jumping around. After putting in new batteries i had no more issues.

The temp gauge is not connected to the SI board in any way. It's only connected with the tach and mpg gauges. More likely you took care of some underlying ground issue when you had it apart.