Gas Tank Sending Unit

[HOT3O2]

Is there any way to bench test a gas tank sending unit? Thanks

[RikerZ28]

Take you ohm meter and but one lead on the sending unit terminal and the other on the mount flange.
See attached link.

https://newvintageusallc.mybigcommerce.com/blog/all-about-senders/

[bertfam]

Sure. You just need to pull the sender and attach it to an ohm meter (set it to 200 ohms or around there). The red positive lead goes to the stud and the black ground lead goes to the mounting bracket. Work the arm up and down and watch the meter change. You can use a digital meter but they take several milliseconds to update so an analog meter is more accurate. The meter should register 0 on empty and 90 on full (approx).

Ed

[169INDY]

Yes. Unmounted unpowered Bench Test.
Using a Volt-Ohm-Meter select Ohms scale.
One lead to the sender output pin other to the sender structure (Ground)
Float (i.e. variable resistor wiper control)
Lowered=0 ohms= 0 gal  (EMPTY)
Raised=22.5ohms= 4 gal (1/4)
Raised=45omhs= 8 gal (1/2)
Raised=67ohms= 12 gal (3/4)
Raised=90ohms= 16 gal (Full)

THis is a theoretical tank curve and not the actual qty, but a good rough idea of float level to resistance "expected"

Jim

[HOT3O2]

Thanks guys, I appreciate the help.

[David K]

If my needle sits at 3 o’clock, how many ohms is that? Got a new one ready to go. 54 years….stuff just doesn’t last anymore.

[169INDY]

On a dash fuel gage, I am assuming 3'oclock is way past Full to the right.

Most likely a open or lack of good ground at the pick up or a open (i.e. fault) in the brown wire from the sender.

A quick check would be to disconnect the in line connector in the trunk and ground the brown (Tan) wire from the harness, which would simulate zero ohms and drive the gage towards empty.

[David K]

Yea, 10 o’clock is empty, 2 o’clock is full. 3 o’clock is closer to quitting time. The tank was empty, so I put almost 4 gallons of high quality California gas in it. Needle didn’t budge, but it will come Saturday….one way or another. I’ll post what happened with pictures if I’m capable.
Interestingly enough, my brothers 67 convertible stranded me across the street from a gas station with 1/4 tank…which was actually empty. Got a new OER unit, dropped the tank today and found the lock ring disintegrated. Took nothing to get it off. Timing is good sometimes. All good now,

[David K]

Gauge read 3 o’clock. Tested it with the tank out, still at 3. Replaced it with a new OER, works now. Apparently they aren’t designed to last past the 55 year mark. 

[169INDY]

So Have you Ever wondered what the inside of the Sender looks Like.
My SS396 (68) Sender (3/8") died and I installed a AC DELCO PN 19179532 to Replace the Factory installed unit.

I took apart the Senders Variable resistor.

Photos;
The resistance wire broke and is Not Serviceable.

[David K]

Indy,
I found the same thing on mine.