What is the OHM reading for a 59 fuel sending unit?

[Smartin]

Conundrum here....

 

59 fuel gauge reads 1/8 tank all the time.  Confirmed gauge is working.  Open circuit drives the gauge to peg at full. 

 

Question is what is the sweep supposed to be for ohms on the gauge?

 

Removed tank and pulled sending unit.  Tested unit and it read 0 to 34 ohms for the full sweep.  Reinstalled unit and tank, making sure unit was grounded well.  Added another 5 gallons to make (10) gallons in the tank.  Fuel gauge still reads 1/8 tank.  I did confirm the float is good.  It's cork and floats in water....unless fuel is less dense than water?  Maybe it's sinking in the tank and not in the bucket of water?

Edited April 15, 2022 by Smartin (see edit history)

[Smartin]

I've seen some gauges like 0-60, or 0-90.  But this sending unit reads 0-30 ish

[Smartin]

CARS doesn't even list a sending unit for a 59, but Fusick does.  The OHM range is not listed, though.  The one for 58 on CARS's site has a 0-30 ohm sweep.  But nothing is listed for the others. 

 

I'm tempted to get one from Fusick to see if it works.

[JohnD1956]

Since you would have to pull the tank again for another sending unit could you try to run the sender unit through it's arc while hooked to the gauge and see how it reads?

[Smartin]

I ordered a sending unit already...will mess with it when it comes in.

[SpecialEducation]

Fuel *is* less dense than water…

 

0-30 should be correct, 0 ohms empty, 30 ohms full. If it’s always reading low it could be a bad ground at the gauge. 

[Bloo]

It's 0-30, and if the sender really does go to zero, it isn't the sender, unless the float is hitting on something and the sender wont go to zero when it is in the tank. 0 ohms is what gets you the "E". Short the sender wire at the back to ground, or better yet your ground wire, at the tank end of the car. The gauge should go to "E". If it doesn't, there is a problem with your ground, or the wiring, or the gauge itself.

 

Make sure the sender goes to zero in the empty tank. Flip it upside down and make sure you get 30 or a little more.

 

Sometimes aftermarket senders in Chevrolets are not capable of 0 ohms at all, and will never work. I have heard of a lot less trouble with replacement senders in Buick circles, but always verify, because some of that really bad Chevrolet stuff probably almost interchanges. True zero is impossible, but it better be under an ohm. Zero your meter so you aren't including the resistance of the test leads in your measurement.

 

Sometimes aftermarket senders need the arm shortened or lengthened or bent to work as all gas tanks are not the same depth. It should be able to go from 0 ohms right side up to 30+ohms upside down, yet not hit on the top or bottom (it comes close). If you want to get it right the first time you should check it with enough gas to bring the sender up from zero ohms, then suck gas out with a HAND PUMP while wiggling the tank until it hits zero again. Then, move the hose to another gas can and HAND PUMP more gas until you run out. Whatever is in the second gas can is the size of your reserve. This is the only way you can know you have a reserve and how big it is, because usually the fuel pickup is on the sender. It should be as low as possible, with the sock almost touching or touching. If it isn't low enough, you will starve for gas before you get to "E".

 

 

Edited April 15, 2022 by Bloo (see edit history)

[Bloo]

4 hours ago, Smartin said:

I did confirm the float is good.  It's cork and floats in water....unless fuel is less dense than water? 

 

Still cork in 59? Wow. I would expect brass. Unless it is a real recent replacement cork, replace it. Back in the day corks were sealed with shellac. Ethanol dissolves it. Re-sealing old corks that have been in gas doesn't work. Bob's has sealed corks with modern sealer.

 

This topic has been debated on this forum and elsewhere. I decided to test it on my 36 Pontiac. I sunk the original corks in gas for a week, and they did not gain weight so I put them back in. One poster on the VCCA forums told me it would work for a few months and then the corks would sink. That is exactly what happened, and they did not feel like corks at all when I took them out. They were obviously heavy. I have new Bob's corks now, and so far they are working fine.

 

For what it's worth, bad corks cause the opposite problem. You'll never get to the full mark with a heavy cork.

 

Edited April 15, 2022 by Bloo (see edit history)

[Smartin]

Thanks for the help guys...I think I just needed to step away from it for a bit.  I had done a similar diagnosis on a 68 Skylark earlier yesterday and started to get tunnel vision.

 

When I disconnected the power wire in the trunk, the gauge shot to FULL which is what I expected.  So that's why it led me to the sending unit.  Either way, I think I'm just going to replace it, since I have one coming from Fusick.  I'll have to siphon that 5 gallon can back out😁

[usnavystgc]

I'm going to chime in on my experience with this.  You probably already know this but, I'm gonna post it anyway.

 

There is a flat, rectangular, non conductive washer that has to go on the stud that holds the sending unit wire.  The washer has to be below the wire isolating it from the nut that holds the stud on the sending unit.  This washer also bends over the top of the stud and protects it from shorting out against the bottom of the trunk.  If both of these points are not isolated from ground, the gauge will always read zero (or in this case, 1/8 tank).  

 

The one pictured below does show a washer isolating the stud from the housing but, the one I bought did not properly isolate it.  Once I fixed that part, the stud shorted out on the bottom of the trunk.  I wish I had a pic of the rectangular washer but, mine was basically dust.  It was just a rectangular piece of fibrous material that was attached to the wire.  It had a hole on one end that slipped over the stud and the other end bent over the top of the stud to isolate it from the trunk floor.

 

BTW, mine was 0-30 Ohms as well.

 

Edited April 15, 2022 by usnavystgc (see edit history)

[Smartin]

I'll be sure to take a look at the current one to see if I missed something when I had it out last.  New unit in transit..

[Smartin]

The answer is 30 ohms😁

 

I drained the tank today and dropped it out.  Zipped the old unit out and installed the new one, with a dedicated ground wire going straight from the unit itself to the body.  Also ran a new wire and all new connections for the power wire.

 

It works.  I will not be draining this thing again.