Issue with temperature gauge when car is warm.

[ohsnapzitsjeff]

525i M50

So I'm having an issue that when the car is warm, the temp gauge on the cluster is 3/4 of the way to the right.

Engine temp live data from my scanner is reading between 86c and 91c (usually locked at 88c) at idle yet the temp gauge line is 3/4 (sometimes slightly over 3/4)…. I feel like at that temp range it should be dead center. Is this a sensor issue? Or is the scanner inaccurate and I’m actually close to overheating? Any ideas? I did replace both coolant temp sensors attached to the head under the intake manifold, i even crossed the connectors to these sensors and the same issue occurred. I also replaced the aux fan temp sensor attached to the radiator to a lower temp one and im running a 80c tstat.

link to video below. This was right after shutting off the car after it was driven for about 30 minutes. Streamable compresses video so much that it is difficult to see the read out, but the video starts with engine temp at 86.8c with temp gauge 3/4 of the way and ends with engine temp at 98.1c with the gauge in the red. I assume that the increase in engine temp is normal under this condition.(hot engine + cooling system no longer running) with that said, IIRC, these temp ranges, even as high as 98c should still be much closer to center.


https://streamable.com/nonadc

Any ideas?

[cirrusblau]

Does your aux fan turn on to high speed when the temp gauge reaches 3/4 or in the red? If it does, then it would confirm that you're overheating and that your live data is wrong.

[ohsnapzitsjeff]

Thanks for the tip! It does not turn on to high speed while the car is running and the temp gauge hits 3/4 and above. I confirmed that the switch attached to the radiator (both the OEM and lower temp one) is functional as I was able to trigger the high speed by pulling the switch from the radiator and holding a heat gun to it. Both switches turned on the high speed setting of the aux fan after reaching the appropriate temperatures with the heat gun.

It’s my understanding that the sensor in the radiator does not send live temp data to the DME, so it appears I may not be overheating.

Now I’m stuck. I’m assuming maybe the sensors attached to the head are faulty so I’ll be replacing those with OEM ones. That said, if either one of those sensors are feeding the live data, then it would stand to reason that the temp gauge wouldn’t behave the way it’s behaving? Also, when it hits red, I get the coolant temp warning on the cluster, is that warning strictly tied to the position of the temp gauge and does not consider temps from sensors? I’m wondering now if it’s an issue with the cluster

[cirrusblau]

Also note that the location of the double temp switch on the radiator is on the exit side where the coolant can already been cooled and sent back to the block. This means that if you reach 88C of the double temp switch, the temp on the thermostat housing (where the gauge sensor is located) would be much higher and you would be probably be overheating at this point. The fact that you've said that high speed fan isn't kicking on would lead me to believe that your temp gauge sensor might be faulty.

[ohsnapzitsjeff]

Temp gauge sensor was faulty. Replaced it with OEM (had a cheap Amazon one in there before) idling with gauge at dead center. Live data has idle locked at 86c. Temp gauge does not fluctuate wildly based on +/- 5 degree increments anymore and stays locked as expected. Thanks guys!

Few notes:
1. It was really obvious in hindsight that the live data pulls from the temp sensor that feeds the DME, the blue one the left. I Tested this by unplugging the sensors.
2. You can easily pull the sensors out without removing the manifold by using a 19mm long socket and a u-joint adapter. Unplug the cable and slot the socket right over the sensor with the u-joint adapter attached, then slide a ratchet with extension through the intake manifold and connect to the u-joint adapter. It was a piece of cake.