Temperature gauge question

[Tom Millward]

Thanks Tony, I’ll have a good read of those posts and try and figure out where my circuit is going wrong.

[Phil Waterman]

Hi

Have not played with it yet but would switching polarity, this is based on the Amp meter if the polarity reverse the needle moves the wrong direction.

Cheers Phil

[Bruce Parker (RIP)]

Tom, if it's a Canadian UC then your gauge is doing exactly what it's supposed to do. Ignition off, with no current going to it, it reads all the way to the right (ie. max). Switch the ignition switch on and the needle, now with current, goes all the way to the left (ie. cold, assuming the engine is cold). As the engine runs it shows the temperature of the engine. I expect if your gauge is reading hot after a good run hill and dale it's because the engine really is hot.

[Tom Millward]

Hi Bruce, my gauge is doing as you say when the ignition is off, but when I switch it on with a cold engine it only goes halfway down the gauge, and reads normal operating temperature (engine is cold). Hence when it starts to warm up (not fully warm) the gauge goes to the right and reads off the scale.

[Tom Millward]

Originally Posted by Phil Waterman

Hi

Have not played with it yet but would switching polarity, this is based on the Amp meter if the polarity reverse the needle moves the wrong direction.

Cheers Phil

Hi Phil, I’ve not tried switching polarity yet, I’ll try that as well.

[Tony Smith]

Polarity makes no difference.

The gauge works by current flowing though a wire winding around a bi-metal strip. As the winding heats the strip, it bends, deflecting the needle on the gauge. The current flow, and the frequency of the circuit opening is dependant on the temperature of the sender on the Cyl Head.

For the gauge to correctly indicate, it needs the correct voltage and amperage flowing through the wire to cause the strip to heat at a certain rate, but polarity doesn't change the heating of the bi-metal strip.

The gauge operates with MORE current showing a COLDER indication, and LESS current showing a HOTTER indication. A full 6v across the gauge should move the needle fully to cold.

Tom, I'd be putting a Multimeter on the back of the gauge with the Ignition on + engine cold, and then again as the engine is running at operating temp (and showing off the scale).

To me, it seems like you are putting less than 6v through the gauge. This could be caused by the 12v reducer not giving you a full 6v at the gauge, or defective wiring with too high a resistance, or a poor ground (either at the Instruments, or engine to hull).

There is also the chance that the gauge or sender are defective, but as they seem to be showing some of the right functions, I would say they are working OK if given the correct diet of electrons.

[Lynn Eades]

Tom, on 6 volts it would work correctly. You need to buy a step down resistor from the likes of Gotham parts, Macs autos or Dennis Carpenter or lots of other vintage parts suppliers, to cut your supply (only to that gauge) to 6 volt The gauge is a 6 volt unit and will not function correctly on 12 volt.

[Tom Millward]

Hello Gents,

I have a voltage step down resistor, and recently changed it to see if that was the issue, but it made no difference. I will check the voltage at the gauge next and try to rule out the senders or gauge. Thanks for the advice.

Tom

[Grant Bowker]

Please understand that I'm not familiar enough with Ford and or Carrier electrics to be considered a "reliable expert". I have the impression that Ford 6V systems actually ran at 4.8 V in part. If I'm right on this and if the converter in use is designed to give 4.8V and if the statement that the gauge system is performing as if it is getting too little voltage are all correct - could this all fit together to make sense?