It seems I have only one nagging problem left on the car. I have just recently reinstalled my dashboard (among other things) after having sent the tach and gauges out for restoration and calibration. The only gauge not working properly now is the temperature gauge.

The first couple times I had the car running after their reinstallation, it worked fine. Started out down at the cold mark, then as the car warmed up, gradually came up to about the half way mark. The first time I noticed anything unusual, I had just turned the ignition on (engine not running), and where the gauge had been at the cold mark before, it was now at the half way mark with the engine dead cold. Started the car up, and the gauge slowly worked up almost to the hot mark. Shut it off, let it cool completely (>1 day), turned the ignition on, and the gauge would only go down to the 3/4 mark (again, with the engine dead cold). It has further deteriorated to where now, with the engine cold and ignition on, the needle is almost on the hot mark.

When I pull the wire off the sending unit, the gauge stays almost at the hot mark with ignition on. If I ground the wire to the sending unit, the pointer buries out of sight past the hot mark.

For reference, the sending unit is <2 years old and is the same one that I had in the car for 4 months with the gauge working fine. The sending unit has not been removed from the cylinder head in the interim.

The LAST thing I want to do is to have to pull the whole dash again and send the gauge back to the repair facility for test and/or repair. Help??

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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

Believe that gage has only two wires going to it, 12 volts and sender. Try running another jumper wire from the gage frame to a known good ground.

John,

You're absolutely right, two wires coming out of the back of the gauge, 12V and sender. There are two threaded studs which hold the gauge to the gauge housing, and which stick out the back of the housing right alongside the spade terminals for the wiring connector. These studs are readily accesible from under the dash. I assume running a ground wire from one of those studs to ground should suffice for what you're suggesting?

Yesterday, I spoke with the company who repaired the gage, and their technician said it sounded like a grounding issue to him also. He asked if the sending unit was seeing a good ground. He said that if there was a sealant used between the sending unit and the cylinder head, that sometimes inhibits path to ground. So, last night I ran a ground wire from the body of the sending unit to both a ground on the body and on the frame, and it was of no help.

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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

[This message has been edited by Bill Pritchard (edited 06-12-2002).]

Bill
I'm known to be backwards once in a while. Believe the sender works by shorting it to ground, the gage goes super hot. Opening the sender wire should leave the gage at cold. You already tried shorting the sender wire and the needle did bury itself super hot. When you opened the sender wire, the gage did not go to cold. From this, the problem is not related to the sender. Problem is with the gage.
I'm assuming since you sent the gage out for calibration, it is a good gage. Also assuming you have 12 volts to the gage since everything else works along with the fact that it drives itself hot.
My WAG on all this is the gage is not getting a good ground. It doesn't have a separate ground lead into it. It gets its ground through its frame. Grounding the frame to a known good ground, with the sender wire open, hopefully will make the gage read cold. I only mean this as a test. If this works it narrows down the problem to a poor gage or poor dash ground.

I'm watching this post BIGTIME! My '69 TEMP gauge goes COLD when the sensor is unplugged and HOT when I ground the green lead. I have a 12ga ground wire from one of the mounting studs Bill refers to, and with the engine running, it never comes off of COLD. While cranking, the gauge sort of quivers at the midpoint, then when the engine starts and the key is released, wham, back to COLD. NO matter if its hot or cold, driving or not, no difference. I even ran a complete new temporary sensor wire from a new sensor (no sealer or teflon tape) to the gauge, NO help same symptoms. I'm baffled. At least the car doesn't puke its coolant out, so its OK, I'd just like to have the gauge work.

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Dave Bradley
www.corvetteforum.net/classics/d1_bradley (http://www.corvetteforum.net/classics/d1_bradley)
'69 SS396 ragtop
'33 3W Coupe
'65 Vette BB Roadster

<BLOCKQUOTE>quote:</font><HR>Originally posted by John_Muha:
I'm assuming since you sent the gage out for calibration, it is a good gage.<HR></BLOCKQUOTE>

Well, it started out being a good gage, because the first couple times I ran the car, it worked flawlessly. And I am sure hoping it's still good, because I DEFINITELY don't want to have to pull the dash again to remove it!! But I guess if the ground wire from threaded mounting stud doesn't work, I'm about out of options.


Dave,

Funny that you have just the opposite problem as me; mine won't go to cold, yours won't come off of it. Yours almost sounds like it HAS to be a gage problem, if you've run a separate sending unit and wire, and have the gage itself grounded.



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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

Dave
Have you tried measuring your sensor at different temperatures? I don't know the values but I believe it should be high when cold (open) and go lower when hot (short).

Bill

This pic (http://www.noneckschevelle.com/images/tachnew3.jpg) is from NoNecks web site. It shows the back of a 69 gauge cluster. Notice that the temp gauge has four posts. The top connects to the sensor, the bottom connects to power, the right side (looking at the pic. or drivers side) is connected to a resistor and the left side is connected to the other side of the resistor and needs to be connected to ground (the metal back of the gauge cluster which should be grounded). Check to make sure the right side post is making good contact with the resistor and that the left side is making good contact with the resistor and ground. If the gauge is not grounded correctly, through the resistor, the gauge will read high.


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TC member 368
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Because Bill confirms the two leads John mentioned (and Bill is right) I am with John. If a good ground lead to the gauge is of no help, the gauge is at fault (sorry Bill). Bill has excluded sender problems by testing open and closed situations. The only other possibility would be the 12V lead to the gauge is much higer (16 - 18 V), but the car is not running during Bill's tests.

Dave's problem sounds to me like a bad sender. If the gauge needle stays at cold, it looks like it senses the sender has a high resistance. Could be a broken wire or a shortage to another 12 V source.
The quivering in the middle might then be caused by the starting sequence which sometimes holds back the 12 V source to the rest of the car to provide the most power to the starting circuit. I don't know if the 69 does this, I have no wiring diagram.

Rob

Elree,

I would assume that the resistor you refer to is integral with the gage, which puts it inside the housing. There is certainly nothing visible on the outside of the housing, and, as I mentioned before, the gage worked that way for several months before I sent it out for refurbishing and even worked the first few times the car ran after it was reinstalled.

John,

Last night, I did as you suggested and ran a ground wire from one of the threaded studs to a good ground. And, assuming Elree is correct, I ran the ground wire to the WRONG stud!! It figures!! Give me a 50-50 chance, and I'll blow it every time. At any rate, there was no change in gage operation last night. I'll switch the ground wire to the other stud tonight and see if that makes a difference.

Many thanks to everyone who is helping out (or at least trying...) here.

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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

OK.... latest from my end. I have a ground wire installed to the PASS side stud, sensor and +12V as indicated on picture and have tightened the "other" post. I had done all this prior to the post update. My situation hasn't changed. I measure the resistance of the sender and it does change with temp (new sender does same) Open sensor wire gauge goes COLD, ground sensor wire at engine, gauge goes full HOT. Hook to sensor, stays COLD. Sensor is at about 100 ohms and varies with temp. I'm lost now.......

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Dave Bradley
www.corvetteforum.net/classics/d1_bradley (http://www.corvetteforum.net/classics/d1_bradley)
'69 SS396 ragtop
'33 3W Coupe
'65 Vette BB Roadster

Dave
Think I'd try hanging a potentiometer on the rear of the gage. Try a 100 ohm linear one. Maybe a multi-turn if you can find one cheap. Disconnect the sender. Clip lead one end of the pot to the gage sender input and the pot wiper to ground. Set it so the gage reads 210, 250 or some number around there. Turn the key off, disconnect the pot and measure its value. May learn something out of this test.

I'll see if I can find some pot, er uh a pot and give it a shot. That's kinda where I was headed. Looks like its time to visit the Shack.

Looks like I will have the unpleasant task of pulling my dash to get the gage cluster out http://www.chevelles.com/forum/mad.gif Tried the ground wire on the other stud last night; no luck.

I think I'll just head to Arizona for a week and contemplate this whole mess........

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Bill Pritchard
69 SS396 Convertible
"Life is short; eat dessert first." - Ogden Nash
My low tech web page (http://home.att.net/~bpritchard/index.html)

Dave. You say the sensor indicates what it should (in a stand alone test) AND you say the sensor varies with temperature. No offence meant, but did you measure the ground of the sensor against the ground of the gauge ?

Rob

Here's an update. I got me a 500 Ohm trim pot (10 turn) and did some investigating. If I hook on right at the end of my sensor wire, (engine end) I get the following readings:

Key ON

Open = Cold
50 Ohms = Quarter way off Cold
40 Ohms = Mid Point
20 Ohms = Hot

The senders range is 400 Ohms Cold to about 80 Hot. Easy to see why the gauge doesn't move.

Looks like the gauge is way too sensitve. Oh, Rob yeah I checked for continuity from the dash to engine ground, less than 1 Ohm. I have ground straps from engine to firewall and gauge assy to firewall. Good info though. Looks like gauge time, That is, next time I take out the dash assy. In the mean time I think I'll hide a temp gauge somewhere. I was looking down near the parking brake area. (Likely spot - out of the way and not too many people will notice)


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Dave Bradley
www.corvetteforum.net/classics/d1_bradley (http://www.corvetteforum.net/classics/d1_bradley)
'69 SS396 ragtop
'33 3W Coupe
'65 Vette BB Roadster

Dave. You blame the gauge. On the other hand it looks like you need a sensor that is 80 Ohms cold and some 20 warm. I know they exist, I think it is VDO or the old Smiths senders.

I can check that at home, tonight or friday. E-mail me if you want.

Rob

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www.si.hhs.nl/~rob (http://www.si.hhs.nl/~rob)

Bill dont do it (come to Az) It's way to blasted hot.
I feel your pain in the gauge dept mine worked the same 3months then kaput.
After sending out to *&* for repair and cal.
I cant tearinto it again because its the daily driver + the wife would snap.
Anyway it's too hot to work on em now.

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Philip Mullaly
72 TPI El Camino
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