Source for replacement coolant temp gauge? - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 08-06-2019, 06:06 PM Thread Starter
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Source for replacement coolant temp gauge?

Coolant gauge on my 1991 500sl has been acting up. It climbs steadily and quickly to max. Engine temp is fine though. I have replaced the temp sensor in the engine already.
I would like to find a new coolant gauge to pop in. Does anyone have a source for one, or a link to repair instructions?
Thanks
John
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post #2 of 10 (permalink) Old 08-07-2019, 01:17 AM
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I've owned many older Mercedes cars, I have yet to see analog coolant temperature gauge fail, on Any of them. It is possible, I suppose, but I'd make sure nothing else is the culprit before replacing it.

How did you determine that coolant temperature is fine? Can you post video what the gauge is doing and explain if this is cold start or engine fully warmed up?

Here is P/N 1295420116, good luck finding new one…. I'd suggest junkyard or eBay… if you Really need one.
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post #3 of 10 (permalink) Old 08-07-2019, 01:20 AM
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I'd be worried the engine temperature gauge might be the faulty one! HAHA
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post #4 of 10 (permalink) Old 08-07-2019, 03:13 AM
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I have same issue on MY Ď91 500SL.

My strategy will be: -
1) engine warmed up. Ignition off. unplug coolant sensor and jump plug with 2no. 470ohm resistors diagonally across socket. Start engine. Does temp gauge come back to life?
Yes? Suspect defective sender unit. Check resistance diagonally across pins of sender. Resistance should be roughly 250-450 ohms.
If gauge doesnít come back to life when you jump socket with resistors and restart engine, go to next.
2) Remove cluster. Unplug cables. Examine. Reconnect. Does this solve problem? No?. Next.
3) Remove front glass bezel. 3 screws. Remove mpg/oil/coolant temp gauge. Pulls straight out. Examine long square profile pins on back of gauge, and corresponding sockets on circuit board. Clean pins with emery paper. Tease sockets with small screw driver so as to make better contact. Refit gauge. Donít refit bezel at this stage. Just reconnect plugs at back of cluster. Restart engine. Problem cured? No? Next.
4) purchase gauge or complete cluster from junkyard. Make sure you get a compatible gauge or cluster. I.e. pre Ď93 in your case. The motors for the gauges inside later clusters have round pins on back, not square. Round wonít fit in square holes. Get compatible gauge and swap over defective combination gauge.

Now, hereís where it can get a bit tricky. Depending on the mileage of the parts car, you might find that the temp and oil gauges work, but the mpg gauge is erratic or doesnít work as good as your old one did. You can swap over the motors, but you need to be 7/10 in DIY skills. It involves removing the gauge needles. Note where the needles sit in rest position. Some rest against a small black pin. To get needles back in correct positions when you eventually put all back together, it is best first to remove these pins before removing needles. The needle will then fall back to its natural rest position. Take photo of this. To remove pins, fold piece of paper/kitchen towel over pin. With small pliers, pull pin straight out. Do not twist or lever. Then remove needles with two small spoons under central boss as a lever. To avoid marking the black face of the dial put sheet of paper under spoons. Once needles removed, grasp tab of black dial face and very carefully lift. Itís sticky and will come off relatively easily without bending or marking the black face. Place dial face to side in clean area. Small screws. Remove and withdraw motor. Swap motors. Rebuild is reverse sequence. Refit needles according to photo you took earlier. Then pins.

Early clusters and gauges are becoming harder to find at junkyards. So if you are only able to source later one with round pins, you can cut the pins off the back of the motors and solder on your old pins on to rear. DIY skills needed? Maybe 8/10. Up to you.

Alternatively you can buy a whole new cluster from MB
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post #5 of 10 (permalink) Old 08-07-2019, 05:59 AM Thread Starter
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Thanks for all the quick replies!
As for jumping the sender, my temp sensor is single pin. When unplugged the gauge goes dead.
I will investigate the gauge using the method you posted and see what I can find.
Thanks again!
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post #6 of 10 (permalink) Old 08-07-2019, 06:10 AM Thread Starter
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Before I dig into the cluster....is there more than one sensor that sends temperature info to the gauge??
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post #7 of 10 (permalink) Old 08-07-2019, 01:14 PM
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I think on reflection that there are three sensors. A 4 pin for KE control module N3. A two pin blue thermistor for the AC fans, and a single pin for cluster. All next to each other on inlet manifold. The test that I was referring to earlier is for the 4 pin sensor and nothing to do with cluster. Sorry.
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post #8 of 10 (permalink) Old 08-07-2019, 02:20 PM
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Quote:
Originally Posted by robm.UK View Post
I think on reflection that there are three sensors. A 4 pin for KE control module N3. A two pin blue thermistor for the AC fans, and a single pin for cluster. All next to each other on inlet manifold. The test that I was referring to earlier is for the 4 pin sensor and nothing to do with cluster. Sorry.
However your scenario might have referenced the incorrect sender, but the methodology is spot on for the correct sender... just need a resistor or two of known value from wire to ground. I don’t have access to what value to use, but you can also ohm sender from pin to ground and see if it shorts or opens with change in engine from cold to hot.
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post #9 of 10 (permalink) Old 08-10-2019, 02:47 AM
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Cheers Ears!

Just so happens @VicoWorld has just posted a photo of the 3 sensors in another thread: -

https://www.benzworld.org/forums/att...386373216.jpeg

Benzworld works in mysterious ways!
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post #10 of 10 (permalink) Old 08-10-2019, 11:22 AM
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Originally Posted by robm.UK View Post
Cheers Ears! <img src="https://www.benzworld.org/forums/images/smilies/thumbsup.gif" border="0" alt="" title="thumbsup" class="inlineimg" />

Just so happens @VicoWorld has just posted a photo of the 3 sensors in another thread: -

https://www.benzworld.org/forums/att...386373216.jpeg

Benzworld works in mysterious ways! [IMG class=inlineimg]/forums/images/BenzWorld2/smilies/tango_face_grin.png[/IMG]
Excellent!

Best Regards...

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