Temperture gauge 1968 deville

[Rdtreur]

The temp gauge on my 1968 instrument cluster is not functioning properly. Is there a easy way to check if the sending unit or the gauge is defect? Is the sending unit the same as for the later style idiots lights?
Many thanks, Ramon Treur

[The Tassie Devil(le)]

The best way to check if the sender unit is not working is to ground it out, and see what the gauge does.

Sender units for Gauges are different than for Idiot Lights.

The Gauge runs on a sliding electrical scale, whereas the Idiot Light is just on or off when the lower limit is reached.

Bruce.

[Julien Abrahams]

And what do you mean with not functioning properly? And how do you know?
x2 on the advice by Bruce. If you disconnect it, the gauge should show no reading at all (to the left of cold) and if you ground it, it should go to H.

[Rdtreur]

Thanks for the reply guys. The meter stays left of cold, or maybe on top of the c. I will check the points you mentioned and report back :-)

[TJ Hopland]

Has this problem just started?  Or has it been there since you have owned or known this car?   

I am assuming on a 68 the gauge sender is underneath the AC compressor?  That is where it is on later models.  It could also be sticking out the front of the block sort of under the distributor. 

If the gauge seems to work by grounding it that points to a sensor issue.  If its a 1 wire sensor sometimes people go crazy with the teflon tape and it ends up insulating the sensor so it can't ground through the block.   To test that use an ohm meter from the body of the sensor to a good ground on the engine.   Or you can jump body to ground and see if that fixes the reading.

Other question is does the engine seem to be running at full temp?    Does the heat blow good and hot?   Are the heater and radiator hoses hot to the touch?   At full temp a typical person can usually touch a hose but would not want to hold on.  IF you can reasonably comfortably hang onto a hose its got getting up to full temp so the gauge may be accurate and you have a stuck open or missing thermostat.   

[DeVille68]

I am assuming on a 68 the gauge sender is underneath the AC compressor?  That is where it is on later models.  It could also be sticking out the front of the block sort of under the distributor. 

I thought the one underneath the distributor is for the ported thermo vacuum switch. Switches from manifold to carburetor vacuum depending on temperature. See the picture attached.

best regards,
Nicolas

[Rdtreur]

After replacing the timing set,  alternator rebuild (and conversion to 1 wire) and HEI installation with new wires and plugs, I could test the temperture sending unit. When grounding the terminal, gauge is in "hot". When motor is in normal operating temp,the gauge is just past the "cold" indication. I think the sending unit is not working properly.
Thanks for al the reply's guys :-)