The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge reads low by 1/4 tank!!!

Been fighting this gas gauge nightmare off and on for very long time,. ignoring for other projects... now back at it but she reads low by 1/4 tank. After issues with aftermarket gauges and senders, was able to find a NOS gauge. I read most if not all the great fixes posted on the Bolt (appreciate all your efforts) Still reading low by 1/4 tank is just not close enough, bent the float rod to get it this good. Checked for good grounds and all that checked out, sender is right on reading 0-30 ohms, new repro sender works but on my 3rd float.

Anyone!

Where does it read when empty?
My 2 trucks with 30 ohm sending units, original gauges, on 12 volts, read 3/4 tank when full, and the needle stops wiggling from gas sloshing when I need to start looking for a gas station. I can live with that.
Carl

Im sure it will read empty as it was reading empty when tank was at 1/4, checked it with a wooden dowel and as I've bent the float rod it's going up.. Will need to fill it up tomorrow and see. I'm thinking it's this aftermarket sender, may be at 3/4 like yours. Thanks

First of all "Good Luck"! I had about the same experience. After messing with the rod, grounds and all the other things one checks I finally I filled a 5 gal. can with fuel, drove to empty so I could get a fix on the real "out of gas" reading, then filled it up. Full it's on 3/4 tank, empty is when the hand just hit's the E mark.

Works for me.

RonR

You might have a leak in the float.

Had two bad ones in a row put new one on today! If this happens again will be looking for something better than brass!

Pretty accurate if you ask me. Tolerances in sender rheostat, tolerance in gauge mechanism/needle position can eat up accuracy on that older system. New parts or not. Chinese or NOS. As evidenced by all the parts, combination of parts and adjustments you've experienced. It shows inherent inaccuracy. Don't stress over this small issue.

There is nothing better than brass. Gas won't eat it. Weigh the float with your drug scale. Hold it down in a container of water for a day. Then weigh it again.

It is possible sometimes to move/bend/adjust needle to get more accuracy on the empty end. You only care about the empty reading. You know when it's full when you fill up.

What evidence do you have that the floats are bad? The brass one's are soldered or brazed at the seam. Should not be hard to reflow or seal with modern agents. Lots of carburetor brass floats out there. Floating up and own.

At this stage, I recommend testing the sender and gauge, together, on the bench, to be SURE the accuracy suits you. Very easy to do. Then seal/reseal the float. Then it will all be OK.

I never trust my old iron's fuel gauges. I always keep an eye on the miles on a particular tank of gas. One lets me know that it is low when it stops running at the stop sign going up the hill next to my house.

Mine never reads full. It is a 20 gal. aftermarket tank located in the rear and I have never been able to put more than 15 gals in when reading empty. Sorry no help here. I think the sender is not installed correctly.

Could be as simple

The 5 hole sender mounting pattern is spaced so that it only clocks/fits one way. We see these gas gauge problem a lot. When it gets to the point of replacing with several units, and frustration sets in, and suggestions aplenty. It is time for a bench test of the gauge and sender together to calibrate or at least see what they do. Be sure the extreme up and down match full and empty depths. This bench test (or sender on the seat test) must be done or you will go broke and crazy. You will have no money to pay the co-pay for treatment. As I already said, when testing is done, then seal the float to be extra sure. I still want to know how it was determined floats were bad.

Possibly you have figured it out already or have decided to become less precise. Like your steering, handling, wipers, brakes, speedometer, oil pressure gauge, ammeter gauge, temp gauge.......

hi all,
the i recently fixed my original gas gauge as it was never reading full
the whole system is completely adjustable for offset and gain, it's pretty neato
here is what i did
i removed the sending unit from the tank and the gauge from the dash and connected them up outside the truck on a large cardboard so i could draw lines for float position reference. see attached photos full..half...empty_gauge
step 1 - make sure your sending unit will read about 0 - 30 ohms full to empty, it's okay if it's not perfect, as long as it is consistent.
step 2 - without power applied, turn your dash gauge upside down and see that the needle slowly falls up to beyond full, and then flip it back and see the needle falls slowly to beyond empty, the needle is free floating correctly
step 3 - wire up the sending unit and gauge for the same circuit as installed.
step 4 - make some marks on the cardboard for the full, half and empty positions for the sending unit so that you can come back to the same positions to see progress towards your desired adjustments
step 5 - carefully loosen the nuts on the gauge and jiggle the position of the coils until you get the needle just right for the float positions
step 6 - don't over tighten the nuts and double check, it should be possible to get nice consistent results

The sending unit should be close to 0-30 ohms for the 50-53 chevy trucks other sending units could be different ranges.
The needle in the dash should be able to free fall beyond empty with gravity, if it gets stuck you must fix that issue first.

hope this helps
-s

Wow! What a great write up. Good job. Very smart. That's my kind of thinking. Probably should show a pic of the nuts and coil adjustment in a close-up or two.
That's the bench test I was speaking of. A VERY nice description of a bench test
Member DADS50 also has pics and a video of his bench test. Did you in fact adjust the coil and did it make a difference?

hi Bartamos,
yeah i was thinking i need a photo of the back of the gauge to better explain
there are two 1/4 inch hex heads that hold each coil
i only had to move one of them, the sender coil side
the way the gauge works is that the needle is pulled to position by two coils simultaneously fighting each other, the needle is in the middle of a magnetic tug-o-war.
one coil is the battery reference coil and the other is the the sender current coil, this way the gauge has very good battery voltage rejection, aka PSRR (power supply rejection ratio), truck off at 6.2V or truck on at 7.4 volts, the needle indicates the same fuel level, actually i have one truck that someone converted to 12V, i think they didn't do anything to the fuel gauge circuit and it appears to be working normal still.

if you want more needle pull, you tweek that coil towards the movement,
after i adjusted my gauge I couldn't tell i had moved the tiny hex head as the position sensitivity is large.
-s

{The 5 hole

Ouch! poison dart at the end there. Are you saying that the "original" style for 1946 or 1953 for sale on Classic Trucks website is not built for the original tanks? Are you saying that the float arm is not clocked to the hole pattern, which is clocked to the tank. So that it automatically orients and fits and works without bending? really? To get the float on the "correct side"? I didn't know that. Boy, I learn something new every year.

They are oriented on the 55.2 and up I have installed.

I've been just using an ohmmeter to check fuel level which is more accurate than the gauge, and mine isn't working anyway. I can easily check fuel mileage even on short trips. With a 17.5 gallon tank,you just multiply the ohm reading by .5833333 to find out how much fuel you use, or have in the tank. Example: 12.5 ohms X .58333333 = 7.29 gallons of gas.

I work on this kind stuff all the time after someone gets done twisting and removing and replacing parts on advice from the internet. Makes me a good living. So drive on. I will withdraw my advice and move on.

My advice, for what it’s worth, is to divide and conquer. One of the two devices is causing your problem. I use a variable resistor 0-100 ohms to check the gauge. Hook it up as you would the sender. Key on. Slowly move ‘pot’ or variable resistor till gauge reads empty. Key off, disconnect pot and measure the ohm value. That will be what your gauge will want to read empty.
Repeat test for gauge for full reading. Now you know if it is truly a 0-30 ohm gauge. Does your sender send the correct ohms at full and empty. If everything is correct, then the only thing left is grounds (which you checked) and the wire from sender to gauge. Possible tohave a high resistance (meaning only a few ohms) connection. Good luck.

Did mock up test per DADS50 and ohms are right on 0-30. Been adding fuel and it appears as I get nearer to full it's closer to being in range. On to other projects, appreciate the help.

Also Im sure these aftermarket senders are off in their range re empty to full. I'm sure if I took the time to dial in the float rod to the tank dimensions could get an accurate reading.

Make sure the float is not leaking.