50 F1 Temp Gauge Malfunctioning

[jetlr1]

The gauge needle stays on "H" while engine is cold, but the needle begins moving left when engine is started and stops about halfway between mid-point of gauge and “C.”. As engine warms up, the needle moves back to the right and stops near “H.”

Any help understanding what would cause this behavior will be appreciated.

Thanks, Joe

[JSeery]

Do you have both the senders? If you do, try jumping the two terminals on the drivers side together. An open set of points on the two terminal will cause the gauge to read H

[Ross F-1]

The way these gauges work is by heating coils wrapped around a bimetallic strip. Over time, the strips seem to lose their full range of motion. Only solution is to replace the gauge when that happens.

[jetlr1]

The wiring schematic shows the temp sensor with 2 wiring terminals on the driver's (left) side of engine. Mine is located on the passenger (right) side of engine. Will this affect the temp gauge's reliability?

[tubman]

I don't believe it would matter much which head which sender was in as long as they are wired correctly. Is there a single post sender in the left (driver's) side? Is there a wire from it going to one terminal of the double post gauge on the right with a wire going from the other terminal to the gauge?

I don't know why someone would do that.

[supereal]

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Before you replace the gauge, remove the senders from the head and clean the threads. The original senders use a "pipe thread' to seal. We sometimes find that a sealant was applied to one or both senders caused the loss of the necessary grounding, affecting the operation.

[flatheadmurre]

If the gauge has been "overloaded" they usually move less smooth then they should and the needle "jumps".
I have rebuilt a -35 fuel/oil gauge converted with the -36 fuelgauge this week that someone bought a "universal 6/12v" aftermarket fuel sender and hooked it up to 12v.
Gauges was all over the place but was able to get them back to working...KS gauges are tough.
The fuelsender was burned to a black lump inside the tank...

[1948F-1Pickup]

Originally Posted by tubman

I don't believe it would matter much which head which sender was in as long as they are wired correctly.

Yup. Doesn’t matter. Mine are “backwards” on my truck.... gauge works just fine.

[jetlr1]

The wiring was correct even though thr sender with two wire connections is on the right side of engine. When I grounded the two wires together, the gauge needle went from "H" to "C". However, as soon as I disconnected them, the needle went back to "H". I then removed the sender with two wire connectors and it appears it came with a red thread sealer that was only evident at top of threads. The threads that were down in head seemed to be clean enough it would have been grounded.

Thanks for all the comments. What next?

[tubman]

If the engine was cold and the ignition was "on", it seems that the gauge is OK.

I would next try connecting the two wires together from the twin post unit (wrap some tape around them to make sure they don't accidently ground out). This will take the two-pole switch out of the equation and see what it does then.

Ignition off, gauge at "H". ignition on with a cold engine, gauge should move to "C". Start engine and let it warm up; gauge should gradually rise to around mid-scale.