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'40 Water Temperture Guage


Ron K.
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When I first start the car the temperature needle comes off of the peg and stops in the normal range, after it is running the needle gradually moves toward the full hot marker. I replaced the sensor on the engine with a spare and the second one reacts exactly the same as the original. Has anybody experienced this and is the gauge adjustable?

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When the ignition key is turned on, the needle drops down from off scale high (hot) to approximately mid-range normal. As the engine heats up while running it gradually climbs to full hot on the gauge (the engine is not overheating). It is as the needle's starting position needs to be adjusted to Cold as a starting point, I assume that it would then climb into the normal range when the engine has warmed up. That is why I asked if there is an adjusting screw for the needle, I cannot see one but it could be there.

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Sounds like the gauge may be weak or out of sync. When you first start the engine (ignition on) the gauge should go all the way to the "cold" and then gradually move towards the normal or mid range. A couple of things to check: the needle itself may be bent or the bi-metal strip in the gauge is weak. These gauges can be adjusted thru a small opening in back of the gauge and this may re calibrate it if the needle is going way past the "hot" with the ignition off. No fun working on these instrument panels. You will need a small blade screwdriver to adjust the tension of the bi-metal strip thru the small opening on the back side of the gauge.

Edited by peecher (see edit history)
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  • 3 weeks later...

Did you use teflon tape on the threads of the sender? It needs a good ground in order to read correctly. You can try grounding the wire to the sending unit for a short period to see if the gauge will reach COLD. If it doesn't, you may not have the correct voltage to the gauge, corroded wire or connections in either the hot side or the ground side of the gauge.

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Are you sure the engine is not overheating? Might be worth borrowing a kitchen thermometer. Lots of weak spots in flathead cooling systems, weak water pump, rust in block or radiator, cap, thermostats (if any) not opening,etc. Be careful opening radiator cap.

Abe

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