Test an electric water temp guage?

Not for accuracy but for operation. How can I make sure it is good or not out of a vehicle?

HOOK IT UP TO A 12 VOLT BATTERY---PUT THE SENDER UNIT INTO A POT OF BOILING WATER---SEE IF THE GAUGE READS CLOSE TO 212 DEGREES f

get a radiator cap with a thermometer/ mechanicle temp gauge right in it, Summit has them for about $20, the rad cap and your temp gauge should read about the same.

I guess I did not make myself clear. The guage does not come off of 0. I am just not sure why. If I connect it to 12v and ground, what should it show, if anything.

If you do that you will burn the gauge out instantly. The way the gauge works is that the sending unit will not pass any current when it is cold, so the gauge registers zero. As the sender unit warms up with engine temperature, it will allow greater amounts of electricity to flow thru it to ground, and this energizes a small electromagnet in the gauge which pulls the needle up higher on the temperature scale. If you hook the wire from the gauge which normally goes to the sender unit up to a ground, it will flow so much current thru the electromagnet that it will burn the gauge out.

It should show full scale deflection, but only touch it for an instance or you will burn up the movement. BTW, if you hook it up reverse it will try to peg the needle reverse.

Brian is correct, the resistance of a sender lowers as the temperature goes higher. The two common sender resistances are 43-51 ohms and 11.5-13.5 ohms (NOT VOLTS). Both are measured at 220 Degrees F.

To test your gauge, you can go to Radio Shack and buy a resistor that is about 50 ohms. Put the resistor between the gauge and the 12 volt supply and connect the negative side of the gauge to ground. You should see a deflection.

A temperature gauge is really a volt meter, measuring the voltage across the resistor. As the sender is cold, the resistance is high and the voltage is low. As the sender warms, the resistance lowers and the voltage increases

yep, same way a gas gauge works, if you could get the resistors right, you could probably use a gas gauge as a temp gauge and the temp gauge as the gas gauge, would drive all the passangers nuts, seing the gas gauge go up as u go down the road, and the temp gauge go down.

Testing Electric Type Indicator

1. Disconnect wire at engine sending unit. Ground wire to
engine block. If gauge registers when ignition is turned
on, you may have a bad sending unit, test as follows.

2. Connect a test light consisting of a 12 volt, 2 candlepower
bulb, & a pair of test leads in circuit by clipping one lead
to battery positive termainal & other lead to body of engine
sending unit. If bulb lights, uint is properly grounded. If
bulb dose not light, check for presence of sealing compound
around threads ot unit. Remove compound & repeat test. Make
sure unit is properly ground before proceeding with next test.

3. Remove test lead from body of sending uint & connect lead to
termanal of unit. If bulb lights, engine sending unit is
internally short-circuited & should be replaced.

4. Remove test light & reinstall wire on Sending Unit.

5. If engine sending unit test satisfactory under the above
conditions, check the following items according to nature
of difficulty.

A. If gauge dose not register when ignition is turned on:
This may be caused by a break in the circuit between the
gauge & the ignition switch or a short between this lead
& ground.

B. If gauge shows high temperature under all conditions; wire
leading from gauge & engine sending unit is shorted
to ground.

C. If gauge registers a low temperature under all conditions,
wire between gauge & sending unit is broken.

Thanks guys. The guage is from a set of Autometer that I bought at a swapmeet. The seller said all worked ecept he could not get a reading from water temp. Just want to see if it is any good. I will try the resistor from radio shack. Joe

Brian's suggestion to use the boiling water approach is right on as it checks everything out in the gage subsystem simultaneously with a pretty well calibrated heat source. Make sure the probe tip is in the water and not touching the pan.

In the car make sure the gage probe fitting is properly grounded as in It1s10 reply.

Kitz

Thanks guys. I grounded the sending unit terminal, the ground terminal, and touched the ign terminal with 12V momentarily and the guage showed full deflection. I will get a new sender. Thanks again. Joe

Hope you don't have to end up buying a new gauge now also!!!

I tired it twice several minutes apart. I hope I dont either, if I do I will still have less than $100 in 6 gauge set. Thanks.