Water Temperature Gauge Pegging Hot Issue

[its55]

I have done all I can think of or know of to resolve the subject issue.  I've done the following;

 

• added the additional engine ground
• added the instrument cluster ground. 
• checked all wiring for continuity, as well as engine to body
• had the instrument cluster out and the temp gauge removed - all appears well visually, connectors tight, etc, not sure what else to check on it / how
• replaced the temp sensor
• I hooked the gauge directly to the temp sensor with it removed from the engine - brown/white wire from instrument cluster to top sensor connector, and grounded the sensor body.  The gauge pegged hot.

 

I’d like to remove the gauge itself and bench test it with a temp sensor if someone can tell me how to do it, ie which wires connect to where.

 

Have I missed something?  It seems like I'm at the point of having to buy another gauge but of course I'd like to avoid that if possible and hate to buy one if I'm just going to get it and have the same issue.

 

Thanks for any help.

 

 

Edited March 28, 2022 by its55
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[jimk]

When you say grounded the instrument cluster, just where exactly did you attach the ground wire to the cluster.  The problem usually is the grounding trace to main harness connector pin 9 for the temperature gauge in the circuit board opens and the instrument ground is lost.

 

So there are 2 choices, one is to run a jumper from the grounding knurled nut on the temp gauge to pin 9 or run it to the chassis.  I ran one to pin 9 and avoided another undocumented wire.

Pin 9 is reliable or he entire instrument cluster electrics would be dead, lights and other electrical instruments.

Edited March 28, 2022 by jimk

[its55]

39 minutes ago, jimk said:

When you say grounded the instrument cluster, just where exactly did you attach the ground wire to the cluster.  The problem usually is the grounding trace to main harness connector pin 9 for the temperature gauge in the circuit board opens and the instrument ground is lost.

 

So there are 2 choices, one is to run a jumper from the grounding knurled nut on the temp gauge to pin 9 or run it to the chassis.  I ran one to pin 9 and avoided another undocumented wire.

Pin 9 is reliable or he entire instrument cluster electrics would be dead, lights and other electrical instruments.

Here's a pic of my cluster grounding (wired to two screws at the bottom) - got this suggestion from a different thread.  Will this work?  Should I switch over to the knurled nuts on the temp gauge side?  Both or just the one under the temp gauge?  Maybe that's the answer...

 

Curious that you say pin 9 because on my main harness connector pin 9 is a white wire associated with head / tailights while pin 11 is the brown / white wire which connects to the temp sensor.  Mine is a '72 model by the way in case that matters.

Edited March 28, 2022 by its55

[jimk]

1 hour ago, its55 said:

Should I switch over to the knurled nuts on the temp gauge side?  Both or just the one under the temp gauge?  Maybe that's the answer...

Pin 9 is when looking at the back of the cluster, it's at 9 o'clock (Or when looking at the wire side of the connector, it's brown).

 

Yes attach to the both nuts, one is on the temp gauge, the other is the fuel level.  Both gauges can have the problem at different times, so ground them now and not have a problem with the other gauge later.

Edited March 28, 2022 by jimk

[its55]

14 minutes ago, jimk said:

Pin 9 is when looking at the back of the cluster, it's at 9 o'clock (Or when looking at the wire side of the connector, it's brown).

 

Yes attach to the both nuts, one is on the temp gauge, the other is the fuel level.  Both gauges can have the problem at different times, so ground them now and not have a problem with the other gauge later.

Thanks, I will try that later today and let you know what happens!

 

[Mike Self]

One more thing to check:  remove the sender unit (you'll need to partially lower the coolant level first) , and use a small wire brush to clean both the threads on the sender and in the water manifold  The sender grounds through the threads, and dissimilar metal corrosion (brass sender, aluminum manifold) will cause enough resistance to booger up the instrument's reading.  Don't use Teflon tape or pipe dope to seal the threads.  Both are excellent electrical insulators.

 

Oh, and clean the terminal and connector too,

 

mike

[ray_]

1 hour ago, Mike Self said:

One more thing to check:  remove the sender unit (you'll need to partially lower the coolant level first) , and use a small wire brush to clean both the threads on the sender and in the water manifold  The sender grounds through the threads, and dissimilar metal corrosion (brass sender, aluminum manifold) will cause enough resistance to booger up the instrument's reading.  Don't use Teflon tape or pipe dope to seal the threads.  Both are excellent electrical insulators.

 

Oh, and clean the terminal and connector too,

 

mike

Yeah, but if he does that, he won't be able to unequivocally state that Jim's solution solved the issue.

 

?

 

Also the ground junction at the voltage regulator (and all the others) should be cleaned up.

 

Cheers,

[its55]

2 hours ago, jimk said:

Pin 9 is when looking at the back of the cluster, it's at 9 o'clock (Or when looking at the wire side of the connector, it's brown).

 

Yes attach to the both nuts, one is on the temp gauge, the other is the fuel level.  Both gauges can have the problem at different times, so ground them now and not have a problem with the other gauge later.

 

Took 30 minutes and changed the cluster ground locations as you suggested and its fixed!!!  Thanks very much, I greatly appreciate the help.

?

[its55]

1 hour ago, Mike Self said:

One more thing to check:  remove the sender unit (you'll need to partially lower the coolant level first) , and use a small wire brush to clean both the threads on the sender and in the water manifold  The sender grounds through the threads, and dissimilar metal corrosion (brass sender, aluminum manifold) will cause enough resistance to booger up the instrument's reading.  Don't use Teflon tape or pipe dope to seal the threads.  Both are excellent electrical insulators.

 

Oh, and clean the terminal and connector too,

 

mike

 

Thanks Mike, I forgot to mention that I had actually done that also.  As you'll see above, the ground wire relocations fixed the problem!! ?

[Mike Self]

11 hours ago, its55 said:

As you'll see above, the ground wire relocations fixed the problem!! ?

It's grounding at the gauge itself that's almost always the problem...and the more direct the ground path, the better.  Running it from the brass gauge retaining nut directly to the car's body fixes the problem (almost) every time.  And by making a "Y" shaped ground, you can attach the other leg to the gas gauge fixing nut, solving a similar flickering problem with the gas gauge.  Both gauges operate on such a tiny resistance current flow that the slightest impediment in the ground path will cause a big time reading problem.

 

mike

[its55]

26 minutes ago, Mike Self said:

It's grounding at the gauge itself that's almost always the problem...and the more direct the ground path, the better.  Running it from the brass gauge retaining nut directly to the car's body fixes the problem (almost) every time.  Any by making a "Y" shaped ground, you can attach the other leg to the gas gauge fixing nut, solving a similar flickering problem with the gas gauge.  Both gauges operate on such a tiny resistance current flow that the slightest impediment in the ground path will cause a big time reading problem.

 

mike

Yep, that's what I did - grounded both! Hopefully I never have that issue again.

[JerryC]

Just to add (maybe less than) 02 cents worth...

It seems to me that those ground wires that are attached to the speedo mounting screws won't do anything for the temp and fuel gauges. There's no metallic connection between them. The gauge housing is plastic, and the temp/fuel gauges are mounted to an insulating circuit board material. No visible current path there to me. I wonder how this fixed someone else's ground problem?

[John_in_VA]

Correct, JerryC.  The wires should go under the two round nuts with the slots, seen on the right side of the photo between the black plastic bulb holders.

[its55]

50 minutes ago, JerryC said:

Just to add (maybe less than) 02 cents worth...

It seems to me that those ground wires that are attached to the speedo mounting screws won't do anything for the temp and fuel gauges. There's no metallic connection between them. The gauge housing is plastic, and the temp/fuel gauges are mounted to an insulating circuit board material. No visible current path there to me. I wonder how this fixed someone else's ground problem?

 

Thanks for the info.  You make a great point and I suspect that it did not really fix their issue because, like me, they may have done all the other things at the same time and thought this did it.  Being ignorant I assumed the metal all connected somehow to provide the ground.  Even my gauge worked for a couple of weeks.  In any event, I'm thinking that its really good now and I do appreciate everyone's input and help.

[jimk]

BMW should have improved the design when the problem started cropping up.  I had to fix mine by 1973 and they continued using the same design til the end of production.