Temp gauge bouncing around

saudivette

Clueless In Sandland
Joined
Mar 24, 2008
Messages
2,633
Location
Aussie expat in Saudi Arabia
I got the BOSS fired up today so I could give it a tune (that's a whole other story - new thread about that too!) and get ready to take it in for a wheel alignment.

Once I got started, the water temp gauge started bouncing around all over the place - full deflection and back, fast enough that the needle looks like it's actually spinning.

Any ideas?
 
Those meters are UNdamped, the only one that is, is the gas level movement....

so a bad connection on the sense side, foil to the gauge itself, plug at the foil , or ground side of the instrument panel...it's electrical...

try jiggling wires see if any affect with key on, engine still....get better 1/2 to watch meter while you play under hood, if not there, hammer with your fist on the gauge cluster....

or reach and jiggle...
 
I'll try that Gene. Stupid question, but where's the temp sensor? I have a switch in the block, just above the starter, with two male blades on it. I can't for the life of me remember what was plugged onto it. The only thing that comes close is the plug with the blue and black wires on it when I replaced the starter harness:

622130K.jpg


What is that plug for?

In the middle of moving house here so all my books are packed away. And, as you all know, I am electrically retarded :clobbered:
 
I'll try that Gene. Stupid question, but where's the temp sensor? I have a switch in the block, just above the starter, with two male blades on it. I can't for the life of me remember what was plugged onto it. The only thing that comes close is the plug with the blue and black wires on it when I replaced the starter harness:

622130K.jpg


What is that plug for?

In the middle of moving house here so all my books are packed away. And, as you all know, I am electrically retarded :clobbered:

The elec booster fan in front of the rad
 
I'll try that Gene. Stupid question, but where's the temp sensor? I have a switch in the block, just above the starter, with two male blades on it. I can't for the life of me remember what was plugged onto it. The only thing that comes close is the plug with the blue and black wires on it when I replaced the starter harness:

622130K.jpg


What is that plug for?

In the middle of moving house here so all my books are packed away. And, as you all know, I am electrically retarded :clobbered:

The elec booster fan in front of the rad
Thanks Jeff. Does the fan plug directly into that plug? My fan plugs into another plug in the harness but I haven't found where the wires run to from there...
 
The needle is supposed to go full sweep in the springy part of the ignition switch, same deal as with the brake warning light, it's to test if the light and gauge are working, if you have a wonky contact in the ignition switch it may cause the bouncing around.

Put the car in a gear (only if your pn switch is working) and try the switch in the springy part, the car won't start but you can check what the needle does
 
The needle is supposed to go full sweep in the springy part of the ignition switch, same deal as with the brake warning light, it's to test if the light and gauge are working, if you have a wonky contact in the ignition switch it may cause the bouncing around.

Put the car in a gear (only if your pn switch is working) and try the switch in the springy part, the car won't start but you can check what the needle does

Nothing like a highly technical term to describe a failure mode....

:hunter:
 
Standard GM test...
turn key to on
remove green wire from sender on drivers side head... needle should go full cold
now ground sender wire... needle should go to full hot
Let us know your results from this test.
If you have access to some resistors let me know and I can tell you what resistors to put inline on the green wire to give your gauge a test reading for accuracy.
A bouncy needle can be a bad connection on any one of the 3 leads going to the gauge.
The start position of the key interupts the power to the gauge and will cause the needle to deflect and should be considered normal.
 
Standard GM test...
turn key to on
remove green wire from sender on drivers side head... needle should go full cold
now ground sender wire... needle should go to full hot
Let us know your results from this test.
If you have access to some resistors let me know and I can tell you what resistors to put inline on the green wire to give your gauge a test reading for accuracy.
A bouncy needle can be a bad connection on any one of the 3 leads going to the gauge.
The start position of the key interupts the power to the gauge and will cause the needle to deflect and should be considered normal.
Thanks mate. I didn't get time to try that today so I'll try tomorrow :thumbs:
 
Standard GM test...
turn key to on
remove green wire from sender on drivers side head... needle should go full cold
now ground sender wire... needle should go to full hot
Let us know your results from this test.
If you have access to some resistors let me know and I can tell you what resistors to put inline on the green wire to give your gauge a test reading for accuracy.
A bouncy needle can be a bad connection on any one of the 3 leads going to the gauge.
The start position of the key interupts the power to the gauge and will cause the needle to deflect and should be considered normal.
Righto, I messed around with said green wire today and eventually found where it's been cut in the past and the ends twisted back together and wrapped in tape. The "join" had come undone with only a couple of strands of wire touching. I cleaned up the ends and soldered them together and now when I take the wire off the sender, it goes to full cold. When I ground the sender, it goes to full hot. I didn't start it yet as I had to "fix" the auxiliary fan switch, but I'll start it tomorrow and make sure the gauge works.


622130K.jpg


What is that plug for?

In the middle of moving house here so all my books are packed away. And, as you all know, I am electrically retarded :clobbered:

The elec booster fan in front of the rad

I tried plugging that plug onto the switch in the block and one of the male contact "blades" came off in my hand. I went into town yesterday afternoon and even though all the spares places recognized the AC Delco part number, no one had a replacement switch. I ordered one on line last night but this afternoon I Bubba'd the old switch and soldered the blade back onto it's stub. Now, does it matter which way on the switch the plug goes? Is the switch just completing/breaking a circuit to turn the fan on/off?
 
The booster fan motor is weak anyways. I highly doubt it does as good as the designers thought it would. I don't think that fan motor is like stronger later model electric fan motors.
 
It certainly doesn't sound as though it's shifting the sort of air the fans in my Dodge do, but I had the fan running today and I can feel air being pulled through from the outside of the AC condenser...
 
Standard GM test...
turn key to on
remove green wire from sender on drivers side head... needle should go full cold
now ground sender wire... needle should go to full hot
Let us know your results from this test.
If you have access to some resistors let me know and I can tell you what resistors to put inline on the green wire to give your gauge a test reading for accuracy.
A bouncy needle can be a bad connection on any one of the 3 leads going to the gauge.
The start position of the key interupts the power to the gauge and will cause the needle to deflect and should be considered normal.
I fired the engine up today and with it running, the gauge bounces all over the place again. Must be a loose connection behind the dash somewhere and it'll have to wait until I gut the interior in the coming months...
 
Success! I bought a new sender unit the other night and just to see if the connection to the gauge was ok or not, I plugged the green wire onto the new unit and connected the body of it to earth and with the key on, hit the end of the sender unit with a little propane torch - gauge swept up and down nicely.

I thought that the old sender unit must be knackered but as I took the wire off the new sender, the wire pulled out of the crimp. I re-terminated the end with a new crimp, flashed up the engine and it all works as advertised!

All console gauges except the fuel gauge work now.

Thanks for the input guys :thumbs::thumbs:
 
Success! I bought a new sender unit the other night and just to see if the connection to the gauge was ok or not, I plugged the green wire onto the new unit and connected the body of it to earth and with the key on, hit the end of the sender unit with a little propane torch - gauge swept up and down nicely.

I thought that the old sender unit must be knackered but as I took the wire off the new sender, the wire pulled out of the crimp. I re-terminated the end with a new crimp, flashed up the engine and it all works as advertised!

All console gauges except the fuel gauge work now.

Thanks for the input guys :thumbs::thumbs:

God is probably envious of you right now, imagine what you could do in 7 days LOL.

fire destroys senders though LOL, not really sure why though that is probably a great mystery of the universe.
 
...fire destroys senders though LOL, not really sure why though that is probably a great mystery of the universe.

I only had it on there for a few seconds. I first tried a glass of boiling water but as the gauge starts at 100*C, it didn't take me long to realise why the needle wasn't moving - especially by the time I carried the glass from the kitchen to the car port :lol:
 
...fire destroys senders though LOL, not really sure why though that is probably a great mystery of the universe.

I only had it on there for a few seconds. I first tried a glass of boiling water but as the gauge starts at 100*C, it didn't take me long to realise why the needle wasn't moving - especially by the time I carried the glass from the kitchen to the car port :lol:


Work on the car in the kitchen, then you don't have to carry stuff outside from there.
 
...fire destroys senders though LOL, not really sure why though that is probably a great mystery of the universe.

I only had it on there for a few seconds. I first tried a glass of boiling water but as the gauge starts at 100*C, it didn't take me long to realise why the needle wasn't moving - especially by the time I carried the glass from the kitchen to the car port :lol:


Work on the car in the kitchen, then you don't have to carry stuff outside from there.
Good call :thumbs:
 
Top