Coolant Temp Gauge Erratic

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passta
Posts: 33
Joined: Wed Apr 07, 2021 12:53 am
Location: Missouri

Coolant Temp Gauge Erratic

Post by passta »

The coolant temp gauge in the cluster is erratic, sometimes it's reading a temp and the needle has moved when up to temp, sometimes the needle is all the way down, to the left. If I smack the side of the dash a few times, it usually starts reading again. I plan to take the cluster out this weekend and see if anything obvious is loose around where the temp gauge connects to the cluster. Any advice on some things to look for in there specific to the temp gauge, or other stuff while I have it cracked open? Can I swap just the temp gauge from a different cluster out of any E24/28?

My car specifically is an 85 Euro M635csi, I don't recall if the temp gauge is different between a regular E24 vs mine and when I moved my collection of non working clusters from E24 and e28's I had, didn't make the cut..
Saint Louis, MO
90 E32 750il
85 M635CSi
15 F10 M5 (gone)
07 E60 550 (gone)
02 E39 540 Touring (gone)
87 E28 535IS (gone)
85 E23 735 5spd(gone)
85 E24 635CSI (gone)
86 E28 535IS (gone)
Jlc
Posts: 287
Joined: Sun Sep 27, 2020 5:27 pm
Location: Atl

Re: Coolant Temp Gauge Erratic

Post by Jlc »

Bad ground?
85 635CSi Bronzit
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RossDinan6
Posts: 295
Joined: Mon Jan 29, 2007 2:35 am
Location: SW FL, USA

Re: Coolant Temp Gauge Erratic

Post by RossDinan6 »

I have battled similar intermittent cluster issues in my '84. Mainly mine were speedo and battery indicator. My solution was to remove and disassemble the cluster. Clean and tighten all the connections. I went so far as to check the resistance from pin to pin on each board. With 3 boards and multiple connectors there are numerous places to get poor connections.

At this point it is working pretty well, with an occasional speedometer needle glitch.
Ross
'84 633 Dinan turbo
passta
Posts: 33
Joined: Wed Apr 07, 2021 12:53 am
Location: Missouri

Re: Coolant Temp Gauge Erratic

Post by passta »

I ended up taking the cluster completely apart, checked all the connections, looked for any cracked or loose solder spots, didn't see anything obviously being the culprit so I will be putting it all back together. While I had it out, I ordered a flocking kit so I can redo the inside of the cluster housing since it was starting to crumble off when I touched things. Speedo gears and all the bulbs are all good already.
Saint Louis, MO
90 E32 750il
85 M635CSi
15 F10 M5 (gone)
07 E60 550 (gone)
02 E39 540 Touring (gone)
87 E28 535IS (gone)
85 E23 735 5spd(gone)
85 E24 635CSI (gone)
86 E28 535IS (gone)
Lbs6
Posts: 19
Joined: Thu Sep 24, 2020 12:17 am
Location: Paso Robles, CA.

Re: Coolant Temp Gauge Erratic

Post by Lbs6 »

You motivated me to fix my erratic fuel and temp gauges this weekend... when the fuel tank was full the gauge would work fine but as the level decreased it would completely fail. The temp was similarly erratic. So yesterday afternoon I extracted the cluster (stupid dash cap made that quit difficult) completely disasembled looking for poor sodier joints. Everything looked good (previous owner replaced programma board) no acid from capacitors. Then I noticed the fuel and temp gauges were mounted to the PC board with a stud and small hex nut. When removed I was able to gently pry each gauge off a pair of large connector studs. Those studs looked a little questionable, so I scuffed them up with with a scotch Brite pad and put the cluster back together. Now both gauges are working as the should. Its amazing how nice it is to have a working fuel gauge.
Leonard
80 633 polaris
79 635 (euro) fjord
85 635 schwarz
songzunhuang
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Re: Coolant Temp Gauge Erratic

Post by songzunhuang »

Lbs6 wrote: Mon Mar 14, 2022 3:19 pm You motivated me to fix my erratic fuel and temp gauges this weekend... when the fuel tank was full the gauge would work fine but as the level decreased it would completely fail. The temp was similarly erratic. So yesterday afternoon I extracted the cluster (stupid dash cap made that quit difficult) completely disasembled looking for poor sodier joints. Everything looked good (previous owner replaced programma board) no acid from capacitors. Then I noticed the fuel and temp gauges were mounted to the PC board with a stud and small hex nut. When removed I was able to gently pry each gauge off a pair of large connector studs. Those studs looked a little questionable, so I scuffed them up with with a scotch Brite pad and put the cluster back together. Now both gauges are working as the should. Its amazing how nice it is to have a working fuel gauge.
Well done! I was going to provide and answer to this thread, but it looks like you figured it out. It took me almost 4 years to figure this one out! I was driving around with jumpy temp and fuel gauges and was never sure what was going on. I took my cluster apart many times but was never brave enough to separate the gauges from the main cluster. It seemed very tight and and I didn't want to break anything. I replaced so many things before I finally performed the simple fix.

I actually saw a video on YouTube where someone fixed this exact same problem and that gave me the courage to give it a go. I am so glad I did. Anyhow, agree with you on how much nicer it is to have a working gauge.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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anchored
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Location: Atlanta

Re: Coolant Temp Gauge Erratic

Post by anchored »

Link to that video?
SHRKATK - Red 87' 635csi
songzunhuang
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Re: Coolant Temp Gauge Erratic

Post by songzunhuang »

anchored wrote: Mon Mar 21, 2022 3:48 pm Link to that video?
Oh I knew that was coming. I ferreted out the link.

https://youtu.be/01N5G6fZTVI

It was exactly the problem I was having and the solution to this post.
The part about removing the gauge and cleaning those little posts starts around 1:45. It's not exactly the same combo gauges as the e24, but the principle is the same.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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