The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge inaccurate

May have missed the subject somewhere, but I have a question about the gas gauge reading on my '50 3100. Cleaned the tank and installed a new sending unit (guessing of Chicom manufacture). After getting everything together, new sending unit, new wiring harness in place, and about 3-4 gallons of gas in the tank, the gauge reads 1/4 full +/-. Get the truck running, I fill the tank slam full---gauge still reads 1/l4 full+/-. Anyone have any ideas why it is not showing full, other than a POS sending unit? BTW, I am running an 8 volt battery instead of a 6 volt, because the local parts house did not have a 6 volt in stock.

https://www.stovebolt.com/ubbthread...as-gauge-on-a-stovebolt.html#Post1475516

That thread is a sticky at the top of this forum.

There are 2 reasons this will happen...One: the sender doesn't register the correct 30 ohms (full) and 0 ohms (empty). Since yours doesn't seem like it is over-registering, I don't think you got the 0 to 90 ohm sender (which was common in newer GM vehicles). Two: you didn't get the float arm adjusted correctly when you installed the sender. There is a formula which I gave everyone 3 or 4 years ago, but sadly it requires some searching and digging to find it now. Essentially you shorten the float arm so that at full (where the sender lever will be stopped on the upper travel) your float just touches the top of your gas tank and at bottom it stops just a bit away from the bottom of the tank. There is one sender unit (designed and made in Taiwan by somebody who knew just what he was doing) and that is the one to get. It comes with the formula for the float bar included. It is sold on the big auction site of the internet by a seller whose ID is renbusan and it is about $30 including shipping.

If it were me, I'd get a handheld meter, remove the sender and check to see the readings at full and empty...and by that I mean where the sender stops will prevent up/down travel. Should be 0 at the bottom and 30 ohms at the top. I'll wait to hear and will look for my formula chart in the meantime.

My gauge reads incorrectly on the 54 because the tank was installed and the suspension was changed. I was sent the wrong coil springs for the front. To low then exchanged for the correct ones later. Eaton Detroit Springs made them wrong. I asked for 2 inches lowered but they used lowered springs and cut an additional 2 inches off. The picture in the gallery at HQ illustrates the stance. After I was there I visited a cousin in VA he lives on a back gravel road and I Leveled off the center line for the county.

I could not find the post from the past so I'll type a new chart for you. Tank depth is self-explanatory. Rod length is not as much so, but the aftermarket (general type) senders are adjustable as for height in the tank...you find the proper height based on your tank depth and then you may have to cut/trim and re-assemble to get the right length. Half of whatever your tank depth is. Float arm length is the length of the float arm...so that it will do its job properly and give you the right arc. Fact is that's what it is all about...putting the central swing point in the center of the tank depth and then adjusting so the float arm has the right arc.

Tank depth...............Rod length..............Float arm length
7"..........................3.5".......................3 3/8"
8...........................4..........................4
9...........................4.5........................4 5/8
10..........................5..........................5 1/4
11..........................5.5........................5 7/8
12.......................... 6..........................6.5
13..........................6.5........................7
14..........................7..........................7 5/8
15..........................7.5........................8 3/8
16..........................8..........................9
17..........................8.5........................9 5/8
18..........................9..........................10 1/4
19..........................9.5........................10 7/8
20..........................10.........................11 5/8
21..........................10.5......................12 1/4
22..........................11.........................12 7/8
23..........................11.5.......................13 1/2
24..........................12.........................14 1/8
25..........................12.5.......................14 3/4
26..........................13.........................15 1/4
27..........................13.5......................16

Given that the reading doesn't change with how much fuel is in it I would suspect the wiring.

My recomendation would be to unhook the wire from the sender (just let it float) and see what the gauge reads, then ground that wire and see what the gauge reads.

If it still doesn't change, then the problem is upstream in the wiring. If it shows full/empty when unhooked and grounded then the gauge is working and you will probably need to pull the sender.

I wrote a thread a few years back that was turned into a “Sticky Thread” on “Troubleshooting a Gas Gauge on a Stovebolt” that may help you work thru your issue. Here is a link. https://www.stovebolt.com/ubbthread...shooting-a-gas-gauge-on-a-stovebolt.html

Check also to be certain your float and float rod are installed correctly. The float has to swing parallel to the sides of the gas tank or it will hang up in travel...could be what yours is doing.

going to get into the gas tank issue when we are able to spend some time on it--right now quite busy. Thanks for the input from all of you; I'm guessing that someone has hit the problem right on the head and I have not seen it.

Do it in the morning if at all possible, amigo. NE Texas is going to be dangerously hot very soon. From what I'm hearing today was our last break from THI of over 115.

Finally got around to checking the gas gauge issue yesterday. Pulled the sending unit out of the tank and found that it is marked 30 ohm. Put it on the bench and checked it with a VOM. At empty position (float all the way to the bottom) it checked 0 ohms. At the very top, it would give anywhere from 30 to 60 before settling down ~30 ohms. When moving from empty to full, it would go absolutely ape--all over the scale! So, I hooked it up to the wiring harness in the truck and got the same results. Move the float to the very bottom, needle shows E. Start moving the float up the scale, and the needle goes absolutely nuts from about 1/4 up to full. Having said all that, I am just going to live with the issue. That is better than spending north of $40.00 plus shipping.
I'll just make sure every time I drive the truck, I go by and fill it back up

Mine would jump like that cause of a poor ground connection.

Thanks for letting us know. The easiest fix for this is the 0-30 ohm sending unit sold on the big internet auction site by a seller whose ID is renbusan. Link to the sender:

https://tinyurl.com/4u894975

$29 and free shipping and you'll be good to go. Good luck!

Well, finally after six months, I got around to correcting the inaccurate reading situation (no need to rush headlong into something so simple!). I ordered the sending unit that Jon suggested from renbusan on fleabay. The instructions that came with the unit are very clear, making it simple for anyone to do the install. The only issue I encountered was that the mounting flange was clocked about 90 degrees from where it should have been to put the float travel along the length of the tank. I corrected that by loosening the center terminal and rotating the flange to the correct position. For anyone doing this replacement--take the gasket and get it oriented in the right position,mark it and use it to mark the flange for correct positioning. I found that the mounting holes are not spaced equally around the perimeter of the flange, so there is only one way for the flange to mount.

Glad this popped up today. Mine is having the same issue. I usually just put 4 or 5 gallons in it when I drive it and check it with a piece of old airhose if in doubt 😁

Now I know where to start 👍👍👍