Temp Gauge is it bad?

[64osby]

My project came with and old Stewart Warner temp gauge. It reads 140 not hooked up. Markings are from 100 to 240.

Trying to figure out if it is shot.

My understanding is that this a 12v system and the temp sensor would limit the voltage from 0 to 12 volts depending on the temp.

As it sits it has no voltage but reads 140. I can hook it up to 12 volts and it will go past 240. Disconnecting the voltage it slowly works it way back to 140.

I'm thinking that an electric temp gauge should either read low (100) or be pegged (240+) when there is no voltage. Is this a good assumption?

For this gauge to read 100 it would need negative voltage.

Thanks for any help.

 

[alldodge]

My project came with and old Stewart Warner temp gauge. It reads 140 not hooked up. Markings are from 100 to 240.

Trying to figure out if it is shot.

My understanding is that this a 12v system and the temp sensor would limit the voltage from 0 to 12 volts depending on the temp.

As it sits it has no voltage but reads 140. I can hook it up to 12 volts and it will go past 240. Disconnecting the voltage it slowly works it way back to 140.

I'm thinking that an electric temp gauge should either read low (100) or be pegged (240+) when there is no voltage. Is this a good assumption?

For this gauge to read 100 it would need negative voltage.

Thanks for any help.

Temp sender is 600 to 800 ohms at 212 degrees or above and 55 ohms or a bit less at 70 degrees. With no voltage being applied to the gauge and it sitting at 140, your gauge is bad

 

[GA_Boater]

Since it slowly returns to 140, the movement is either dirty or sticky or busted. Also with it pegging with 12V, 0 volts should be at the low end of the scale and as the temp increases so will the voltage. Rather than using 12 volts, try a 9 volt battery. See how high it goes and reverse the polarity to see if it goes to less than 140.

You had good luck with opening the tach, may be you can open the temp gauge and fix it

 

[gm280]

Before throwing it in the trash, It really sounds like the internals have moved out of position with the dial readings. If you can open it up, you could just reposition it and close her up again and use it. If it is sealed, then what are you seriously going to loose trying to reset the guts to the correct position again... it could just be the pointer itself that moved as well... JMHO!

 

[64osby]

Was able to get the chrome bezel off. Nothing broken yet.

Moved the needle to 100, put 12V on it and it went to 180.

There are two tiny rivets holding the face on. I'll try getting that off. See if cleaning it would make a difference.

Thanks and I'll let you know.