71 Temperature Gauge issue
Thread Starter
Melting Slicks
Joined: Mar 2005
Posts: 2,093
Likes: 297
From: Midlothian VA
71 Temperature Gauge issue
I've searched on this topic several times and have found nothing so here's hoping I'm not the only one to see this issue.
Stock original 1971 temperature gauge functions normally when vehicle is running. Upon start up it rises as the engine heats up and holds a normal reading once the thermostat opens.
Issue occurs when I cut the car off. When I turn the key from the run to the off position the gauge needle instantly drops counter clockwise past the lowest reading on the scale and falls until it's near the "water" text on the gauge face.
When the key is turned back to the run position (engine on or not) the needle jumps back up to a normal position on the gauge face.
Anyone else seen this? Is the gauge defective? Is it a grounding issue?
No biggie but it's annoying.
Stock original 1971 temperature gauge functions normally when vehicle is running. Upon start up it rises as the engine heats up and holds a normal reading once the thermostat opens.
Issue occurs when I cut the car off. When I turn the key from the run to the off position the gauge needle instantly drops counter clockwise past the lowest reading on the scale and falls until it's near the "water" text on the gauge face.
When the key is turned back to the run position (engine on or not) the needle jumps back up to a normal position on the gauge face.
Anyone else seen this? Is the gauge defective? Is it a grounding issue?
No biggie but it's annoying.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Hammer-
Yep! When power is cut from the gauge it will float.
Yes its a bit strange that it floats so far downward and I'd have to say that the oil inside the gauge (spindle) housing has probably leaked out. Would I replace the gauge in this car? Probably not. I think that as long as the gauge is working fine in the on position I'd leave it alone.
Unless of coarse this is bothering you and then by all means I'd replace the gauge.
Willcox
Yep! When power is cut from the gauge it will float.
Yes its a bit strange that it floats so far downward and I'd have to say that the oil inside the gauge (spindle) housing has probably leaked out. Would I replace the gauge in this car? Probably not. I think that as long as the gauge is working fine in the on position I'd leave it alone.
Unless of coarse this is bothering you and then by all means I'd replace the gauge.
Willcox
Thread Starter
Melting Slicks
Joined: Mar 2005
Posts: 2,093
Likes: 297
From: Midlothian VA
Thanks for the sanity check Willcox.
Good to know that it's not a wiring/sending/ground issue.
Probably wouldn't be so annoying if I didn't have anything to compare it to. The needles on the temp gauges of my other 71 & my 72 both stay where they are when the key is placed in the off position.
I agree with your replacement assessment so going forward I guess I'll just continue to avert my eyes.
Good to know that it's not a wiring/sending/ground issue.
Probably wouldn't be so annoying if I didn't have anything to compare it to. The needles on the temp gauges of my other 71 & my 72 both stay where they are when the key is placed in the off position.
I agree with your replacement assessment so going forward I guess I'll just continue to avert my eyes.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Y do u need to read the temp with the engine off?
For an easy test you can remove the temp sender from the head and stick it in some boiling water. U need to be creative here and use some extension wire to the harness with the brass body connected to ground while you get some boiling water going nearby. This will give you a 212* mark and should be good enough for a quick verification test. U can also use a thermometer to watch the temp rise but be careful with the hot water.
good luck,
cardo0
good luck,
cardo0
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Same here Roger. I would have to guess all the resistance oil is gone from the gauge. That's about the only thing that would case a gauge with no power to drift like that.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I can't remember , besides no input signal what makes the needle go full cold ? Does a missing ground make the needle go cold ? Guess I could go out and check but its about 20 degrees in my garage right now.
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Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Why so fast though ? I would like to see how the gauge reacts if the gauge fuse is pulled instead of turning the key off.
I can't remember , besides no input signal what makes the needle go full cold ? Does a missing ground make the needle go cold ? Guess I could go out and check but its about 20 degrees in my garage right now.
I can't remember , besides no input signal what makes the needle go full cold ? Does a missing ground make the needle go cold ? Guess I could go out and check but its about 20 degrees in my garage right now.
With no ground the gauge would peg past the rivet about 1/8". Without signal it would go to cold and grounded it would peg to the rivet.
Based on that if the gauge had power it would respond to the missing link, but without power.. it's just a needle that floats in it's housing and the only obstruction would be the dampening fluid.
Wonder about back-feed voltage! Well it can't be that.. it would cook the gauge when the key was turned on with two poles powered up. I really don't know the answer to this one Roger..
Though you were in Florida?
Thread Starter
Melting Slicks
Joined: Mar 2005
Posts: 2,093
Likes: 297
From: Midlothian VA
Why so fast though ? I would like to see how the gauge reacts if the gauge fuse is pulled instead of turning the key off.
I can't remember , besides no input signal what makes the needle go full cold ? Does a missing ground make the needle go cold ? Guess I could go out and check but its about 20 degrees in my garage right now.
I can't remember , besides no input signal what makes the needle go full cold ? Does a missing ground make the needle go cold ? Guess I could go out and check but its about 20 degrees in my garage right now.
Results:
Insert key and turn to run/on position - needle jumps from just above the "w" in water to just below the 100 degree number on the gauge.
Turn key off - needle drops back to just above the "w".
Turn key on - needle jumps back to 100 degree mark
Remove fuse - needle falls back to just above the "w"
So removing the fuse has the exact same result as turning the key off - makes sense.
I agree with Willcox on this one, a lack of damping fluid allows the needle to drop due to the simple weight of the needle. When power is applied to the gauge the needle responds like any normal gauge until the power is disconnected.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Ok, I just went out and tested this despite it being just 21 degrees here.
Results:
Insert key and turn to run/on position - needle jumps from just above the "w" in water to just below the 100 degree number on the gauge.
Turn key off - needle drops back to just above the "w".
Turn key on - needle jumps back to 100 degree mark
Remove fuse - needle falls back to just above the "w"
So removing the fuse has the exact same result as turning the key off - makes sense.
I agree with Willcox on this one, a lack of damping fluid allows the needle to drop due to the simple weight of the needle. When power is applied to the gauge the needle responds like any normal gauge until the power is disconnected.
Results:
Insert key and turn to run/on position - needle jumps from just above the "w" in water to just below the 100 degree number on the gauge.
Turn key off - needle drops back to just above the "w".
Turn key on - needle jumps back to 100 degree mark
Remove fuse - needle falls back to just above the "w"
So removing the fuse has the exact same result as turning the key off - makes sense.
I agree with Willcox on this one, a lack of damping fluid allows the needle to drop due to the simple weight of the needle. When power is applied to the gauge the needle responds like any normal gauge until the power is disconnected.
I'm 14 right now.. can't stand this damn cold... Now way would I venture out until warmer temps..
You sir get a 
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I tried to head south sat 27 ,phone rang as I was walking out the door,girlfriends brother-in -law died of a massive heart attack,48 years old 
buried him friday the 3rd.
Sat the 4th I headed south,just past Corbin I spun the car out and totaled it.
I'm going to try again this Sat.
buried him friday the 3rd. Sat the 4th I headed south,just past Corbin I spun the car out and totaled it.
I'm going to try again this Sat.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Ok, I just went out and tested this despite it being just 21 degrees here.
Results:
Insert key and turn to run/on position - needle jumps from just above the "w" in water to just below the 100 degree number on the gauge.
Turn key off - needle drops back to just above the "w".
Turn key on - needle jumps back to 100 degree mark
Remove fuse - needle falls back to just above the "w"
So removing the fuse has the exact same result as turning the key off - makes sense.
I agree with Willcox on this one, a lack of damping fluid allows the needle to drop due to the simple weight of the needle. When power is applied to the gauge the needle responds like any normal gauge until the power is disconnected.
Results:
Insert key and turn to run/on position - needle jumps from just above the "w" in water to just below the 100 degree number on the gauge.
Turn key off - needle drops back to just above the "w".
Turn key on - needle jumps back to 100 degree mark
Remove fuse - needle falls back to just above the "w"
So removing the fuse has the exact same result as turning the key off - makes sense.
I agree with Willcox on this one, a lack of damping fluid allows the needle to drop due to the simple weight of the needle. When power is applied to the gauge the needle responds like any normal gauge until the power is disconnected.
