[Monkey Wrench]

I think if you look at the temperature guage basiacally as a volt meter that basically what it is.

as an example if you pick up an older analog meter, it uses the same needle ( gauge) for checking resistance, voltage and current. the difference is in the switching inside the meter . it applies different resistors (shunt resistors) so when you change the voltage scale you are employing different internal resistors.

would it be possible to separate the rest of the wiring and see if applying a small voltage to the gauge, lets say just power it off one or two DC flashlight batteries, see if the needle moves?

if you connect it backwards maybe youd see the needle move backwards so Id confirm polarity before sending it any appreciable voltage.

I think what is happening is the guage is provided power , it goes through the gauge and then to the temp sensor, the tempsensor is a variable resistor, the variable resistor is such that it is temperature dependant.

you could also check through the temp sender to ground and measure resistance through it and I would think that as the temp rises the resistance would be either greater or less. Point is you shoud see some reaction in terms of its resistance to ground, and that resistance changes with temperature.


when the resistance is increased , it is in series with the 12V battery so you have two voltage drops, ont through the guage itself one through the resistor then back to the battery. the sum of those two voltage drops is 12 V

because the temp resistor varies it's resistance by way of heat acting upon it ,thus changing its resistenace, well, since the two are in a series circut lower resistance means the resistor ( temp sender) takes a larger share of the 12 V and if it is no resistence the guage would see full 12 V any resistance that the sender presents shares the series load , leaving less , or more power for the gauge so the gauge reacts upon the voltage it sees.

it is labled as a "temp sensor" but I think t it is actually just a volt meter, with a painted dial representing the temperature, rather than "volts"

I think if you sub in a meter for the guage youd see some voltage differential which is dependant upon the temparture of the sender unit

so in theory of you were to re-paint the dial of a voltmeter so it represnted temperature it would then dispay engine temperature, where those marking s fall, thats callibration.


also try this, when the engine is warm, give the dash near the guage a "thwack" with your finger to shock it. sometimes the needle can be rubbing.so then the guage is itself mechanically stuck.


my volvo fuel guage does that, it will read Im empty, i fill up, no movement, then I give the dash a little thwack and the meter responds to half tank or full or what it is. the needle is definitely mechanically binding. I just live with it.

the fuel guage isnt; any different really except that the variable resitor is in the fuel tank.

when you have two loads in series, they share the voltage, they each have a voltage drop and the two voltage drops add up to 12 V

the sender is varying the resitance and the guage displays its share of the 12 V . you may say whats left of the 12V is what the guage sees.

the callibration is merely how the face of the guage is painted. I think if you just think of it as a voltmeter, it may simplify things.

there is some chance I am off on some of this so to all readers, do feel free to correct me if you do not agree with the explanation above.

I think you said you have 12 V at the guage, god, then the other side should have a variable resistance. a poor connection or wire break or wire rubbing through to ground may mess wiht the result. I bet if you ground that wire to the sender it will peg the meter, it is seeing no voltage drop then and the gauge would then see full 12 V and so the needle reacts by going to it's maximum scale.

usually with meters it is best not to try to make the meter needle go backwards or to force the meter to peg.

same will happen on an analog voltmeter if you are taking a measurement but you are on the wrong voltage scale or connect it backwards, this action can possibly damage a meter..

back in the early days of electrical bench work, a bench tech did likely not have fancy DMM's or multimeters . they took years to develop and he may only afford the one meter.

so insteead he would just use one meter and he would know how to use shunts to take various other measurements.

he'd be appying resistors and things , the modern analog meter just takes the hard thinking away, it still works the same way. its easier to set the switch to a certain voltage scale than to think about what resistor to apply.

digital meters or DMMs they will still show voltage but they use "magic electronics" some are "autoranging" so then you don't even have a switch to change the scale, the meter does it for you.

DMMs can sometimes present you with erroneus readings. it may for example measure voltage although the amperage is miniscule, so then you can get irrellivant readings,

for this Id use a basic analog meter. easier to watch the needle swing than read a bunch of flickering and changing numbers.. some DMM's do have a bar graph function thing to give a more analog representation.


nothing about the gauge is AC, frget anything about AC power here. it is just a DC voltmeter painted and callibrated as a temperature guage.

a user of a DMM may put his probes on something and there can be a DV voltage and as well some AC component. that can sometimes cause confusion.

as an example a 12V DC power supply for example or a battery charger makes DC but the power is probably not very well "filtered" by capacitors , then there may be DC but with a AC component, referred to as "dirty power" - you need clean power to for example run a radio but the power does not really need to be "clean" to charge up a car battery.

the car battery produces clean DC, the alternator may create dirty AC and the battery helps smooth out the AC ripple. when the car is not started the battery is providing clean DC.

i do not think the problems of the temp guage have anything to do with AC ripple. its just good to be aware you can sometimes see DC and and AC component from the same source. - just to avoid confusion for when you measure where both exist..

sometimes people get confused when using a DMM. and then realize they havent chosen the correc scale or swtitched the meter to the appropriate choice of AC or to DC

to confirm maybe just measure a 1.5V flashlight battery or a 9V then you can see the meter react, it just verifies it is working properly and as expected.

when working on home plant electrical work
Ill do that before I go trusting a meter to prove ther is or is not any power before touchign a wire.

Ill walk ot an outlet , and confirm yes theis meteer is able to measure 110. then I know the meter works and I am then more confident that I am not making a dangerous mistake. you can walk to the car battery and check the meter yes it is near 12 V so yes, the meter itself is functional. some cheap ones have intermittents loose batteries, cracked circuit boards, etc. you get what you pay for , Fluke is usually a good brand so I will not use on higher power like 600 V measurements, it doesnt; have high enough internal resistance protection.

a radio shack cheapo is fine for car use , usually.

it could be possible you have the wires to the guage swapped? that may try to drive the gauge backwards. same as if you had hyour meter probes reversed.