1956 temp gauge problem

[Jeff B.]

The temp gauge needle rests all the way to the left when ignition is off and engine cold. When key is turned on, the needle moves to the right about 1/4 inch, just about even with the first dot past the 100 mark. The needle still shows this same, slightly "warm" reading even if temp wire is unplugged from sending unit. When engine is hot, the needle shows about 220 degrees, but doesn't seem to actually be that hot.
Any ideas why gauge doesn't read properly. The gas gauge, in that same cluster, works fine.

[Richard M.]

Re: 1956 temp gauge problem

Jeff, Remove the wire from the sending unit and attach it to engine ground and it should peg the meter.

If it does, the sender is likely the problem. Before you replace it, replace the sender wire terminal onto the sender, then take a wire and hard ground the sender base/body and see if the reading changes. If so, take a wrench and turn the sender a few turns backward and forward several times. If the sender was installed with sealant, which is not recommended, this will re-ground the sender better and may be the issue. If no change, replace the sender.

Rich

[Mike M.]

Re: 1956 temp gauge problem

rich is right on.if u find the temp sending unit is the culprit, i'll give u a nos ac deco pin style 56 sending unit as i've got a few and no longer have a 55 or 56. send me a pm is u need one. mike

[Mark S.]

Re: 1956 temp gauge problem

Mike: Your passion for the hobby and your continuous generosity is one of the high points of belonging to NCRS! Mark

[Mike M.]

Re: 1956 temp gauge problem

mark:the augusta midget, carlton, has phoned Pope Francis, suggesting i too be canonized. however, i suspect i'll rot in hades with all my buddies. regards, mike

[Jeff B.]

Re: 1956 temp gauge problem

Jeff, Remove the wire from the sending unit and attach it to engine ground and it should peg the meter.

If it does, the sender is likely the problem. Before you replace it, replace the sender wire terminal onto the sender, then take a wire and hard ground the sender base/body and see if the reading changes. If so, take a wrench and turn the sender a few turns backward and forward several times. If the sender was installed with sealant, which is not recommended, this will re-ground the sender better and may be the issue. If no change, replace the sender.

Rich

Rich:
Thanks for your input. Here are the findings:
Engine cold:
With key off, temp needle lays all way to left, showing "dead" cold.
With key on, temp needle moves to first dot past 100 (~120-130 degrees ??). When wire is unplugged from sender, needle does not move.
With key on and temp wired is grounded, needle pegs past 220.
Hard grounding sending unit makes no difference.
When engine starts up, you can see the needle move slowly up past 180 and stop at around 220; unplugging the wire at sender drops needle back to the first dot past 100. A new 180 degree thermostat has been installed.
My current question is: when key is on (cold engine) and needle is at the first dot, shouldn't the needle drop back to "0" when wire is disconnected from sender? Maybe the gauge itself is out of calibration?
Thanks again for your insight.

[Richard M.]

Re: 1956 temp gauge problem

Rich:
Thanks for your input. Here are the findings:
Engine cold:
With key off, temp needle lays all way to left, showing "dead" cold.
With key on, temp needle moves to first dot past 100 (~120-130 degrees ??). When wire is unplugged from sender, needle does not move.
With key on and temp wired is grounded, needle pegs past 220.
Hard grounding sending unit makes no difference.
When engine starts up, you can see the needle move slowly up past 180 and stop at around 220; unplugging the wire at sender drops needle back to the first dot past 100. A new 180 degree thermostat has been installed.
My current question is: when key is on (cold engine) and needle is at the first dot, shouldn't the needle drop back to "0" when wire is disconnected from sender? Maybe the gauge itself is out of calibration?
Thanks again for your insight.

Jeff, Based on your thorough tests, yes it seems the gauge may be a issue if it doesn't zero with key off. It may be a mechanically sticky needle. But you may need to narrow it down more. The harness sender feed wire could have a low grade short to ground, or the Power wire from the IGN terminal on the Ign switch to the gauge could be faulty. It's tricky, but get behind the dash(Key off or Battery off), and check the terminals at the gauge. You may have some corrosion on the terminals. Remove the terminals and check for cleanliness. Clean if you see aged connections.

Also check to be sure there is a good ground on the gauge pod. The gauge pods are crimped to the meter bezel cases and the pod gets its ground from the dash reinforcement via the mounting Palnuts on the tabs of the pods. Sometimes you just need a little tighten up on the Palnuts to refresh the ground connection. You can run a jumper from the ground lug on the dash near the headlight switch or the EBrake firewall bolt Gnd Buss directly, or out to the engine as a test too.

I have a chart with the Sender resistance readings at various temperatures but not handy right now. You can put a ohm meter on the sender when cold and get a reading, then at various temperatures as the engine gets to normalized temperature. If you have a IR Gun you can compare those values to the gauge readings too.

Based on results of these tests and checks, it may help narrow it down more to prove if the gauge meter is the culprit.

Rich

[Jeff B.]

Re: 1956 temp gauge problem

Thanks to all who responded. All said and done, I think the gauge itself is at fault since it does register slight temperature when the key is turned on with a cold engine, and does not drop back to "0" when the temp wire is disconnected from the sender.
Also discovered that when the key is on, the temp wire will read ~12 volts. Is that normal?
Thanks again for everyone's input.

[Richard M.]

Re: 1956 temp gauge problem

Thanks to all who responded. All said and done, I think the gauge itself is at fault since it does register slight temperature when the key is turned on with a cold engine, and does not drop back to "0" when the temp wire is disconnected from the sender.
Also discovered that when the key is on, the temp wire will read ~12 volts. Is that normal?
Thanks again for everyone's input.

Jeff, Yes it sounds like the meter but check that other stuff too to be sure.

edit.... The sender is a resistor to ground in the circuit and you will read voltage on the sender wire, although I never got accurate readings. Another idea is to measure resistance of the sender pin tip to ground, cold, then warm, then hot. It should vary. I couldn't find my sender resistance chart so I can't give you values.

Rich