• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

fuel gauge not reading full

Dne'

Dne'

Well-Known Member
Hi!
My fuel gauge never goes to full(more like a little over half tank) after filling. I know it must be in the new sender that I installed, so how do I go about getting it to measure the fuel level more accurately? Just take it out and bend the float arm?
dne'
 
Somewhere on this forum , this topic has been tackled thoroughgoing .IIRC
CMAYNA knows about that stuff.
 
Cmayna has an entire post on his jig to adjust them. Might PM him about your problem.

Bending the float arm is one way. I have used 4 gal of gas (1/4 tank) in a '66 tank to adjust. Must drain gas for each adjustment. Usually, after 4 times of draining, I get it right on at 1/4 tank. To me, the low side is what you want as close as possible.
 
Dne'
What gauge are you using? Reproduction sending unit? Plastic or brass float? What size tank? Can I assume you got the right sending unit to match the size of the tank?

AZ has a very good point that it is most important to have the gauge reading accurately when at 1/4th tank. Is this level correct? Odds are it is not if your full is reading something less.

Can I assume you did not check the ohms reading of the sending unit before you installed it?


If the fault lies because the float arm is not bent correct you can bend the arm, at a specific point to make it read either higher or lower.


So much to learn.
 
Problems as dramatic as this are usually related to a mis-match of the gauge and sending unit, and either one being mis-matched to the supplied voltage (CVR).
 
This is one time you can use the work Assume~ I did not check the ohms reading of the sending unit. the gauge is a stock fuel gauge, 16 gallon tank and repop sender switch. To check the actual fuel gauge, I can ground the wire at the sender switch and that should make the needle go all the way to Full, correct? Then if that is ok, then I can play with the sender arm?
"cmayna" said:
Dne'
What gauge are you using? Reproduction sending unit? Plastic or brass float? What size tank? Can I assume you got the right sending unit to match the size of the tank?

AZ has a very good point that it is most important to have the gauge reading accurately when at 1/4th tank. Is this level correct? Odds are it is not if your full is reading something less.

Can I assume you did not check the ohms reading of the sending unit before you installed it?


If the fault lies because the float arm is not bent correct you can bend the arm, at a specific point to make it read either higher or lower.


So much to learn.
Click to expand...
 
Yep......and when you take the sending unit out to work it, measure the ohms range just to be sure it works right to begin with.

As Mid mentioned......the CVR could be a problem also. Are the other gauges (oil and water) reading correctly?
 
Assuming the CVR is OK, when you ground the sending unit's wire and the gauge reads full then the gauge is probably not the problem.

I asked if the bowl is plastic or brass for the cheap plastic ones are known to leak and thus will take on some gas dropping the arm down into the gas too much resulting in a low reading.

If the bowl is not leaking then yes you can tweak the arm. Below is a pic of a sending unit in place bolted to my sending unit fixture which is a lower piece of a retired gas tank. If the gauge is reading low as in your case, you basically want to straighten the arm out a tad. i would take two pliers grabbing each upper arm A and lower arm B right at the elbow (C) and slightly straighten the elbow out just a tad.

What you are really doing is changing the angle of the upper arm A. Straightening the arm raises the readout whereas increasing the bend of the arm lowers the reading.

Do you have a drain plug in the tank? If so then I'd drain the tank all the way, put back in exactly 4 gallons. Check the reading. Odds are it is reading zero or 1/8th of a tank. Drain the tank again, remove sending unit and tweak (straighten) the arm just a tad. Re install and do the procedure again. Very time consuming to say the least.

If you don't have a drain plug then it gets very difficult and that might be the time to consider getting a new tank with a drain plug. I have never had to deal with a tank that does not have a drain plug.


What I did was to get another retired tank and cut a big hole out of the top so I could see down into the tank at the sending unit. I'd fill the tank with 4 gallons to represent a 1/4th tank of a 16 gallon unit. Measure the height of the float to the bottom of the tank. Make a pedistal with the height of the same dimension. Now I can simply install a sending unit to the fixture as shown below, raise the float and install the 1/4 tank pedistal. Hook up the gauge sending wire to the sending unit, ground the fixture to the car's chassis and turn the key on. The needle will then go up to somewhere near 1/4 level. If the reading is off, I can simply tweak the sending unit's arm until I get a exact reading.

Whoola! All done tweaking.

Install the sending unit back into the car's tank and call it a day.

FuelSendingUnita.JPG
 
Last edited by a moderator:
Darn if this isn't the neatest response I've ever gotten! I love the actual diagram using part of a gas tank! The explanation is, well ,I can do this! I do have a drain plug, I have a metal or brass float, I have an electronic CVR that works very well(no fluctuating lights or flickering). eeyah, I have to 'assume' that the sender is correct for my 16g tank. This is on my list of "to do's". I still have to pull the gas neck out and modify it like Tarafied showed me! So two gas tank projects in one! Amazing how much time would have been saved if having known stuff like this during assembly!
thanks for the wonderful responses from ya'll! :bowdown always something to learn!
dne'

"cmayna" said:
Assuming the CVR is OK, when you ground the sending unit's wire and the gauge reads full then the gauge is probably not the problem.

I asked if the bowl is plastic or brass for the cheap plastic ones are known to leak and thus will take on some gas dropping the arm down into the gas too much resulting in a low reading.

If the bowl is not leaking then yes you can tweak the arm. Below is a pic of a sending unit in place bolted to my sending unit fixture which is a lower piece of a retired gas tank. If the gauge is reading low as in your case, you basically want to straighten the arm out a tad. i would take two pliers grabbing each upper arm A and lower arm B right at the elbow (C) and slightly straighten the elbow out just a tad.

What you are really doing is changing the angle of the upper arm A. Straightening the arm raises the readout whereas increasing the bend of the arm lowers the reading.

Do you have a drain plug in the tank? If so then I'd drain the tank all the way, put back in exactly 4 gallons. Check the reading. Odds are it is reading zero or 1/8th of a tank. Drain the tank again, remove sending unit and tweak (straighten) the arm just a tad. Re install and do the procedure again. Very time consuming to say the least.

If you don't have a drain plug then it gets very difficult and that might be the time to consider getting a new tank with a drain plug. I have never had to deal with a tank that does not have a drain plug.


What I did was to get another retired tank and cut a big hole out of the top so I could see down into the tank at the sending unit. I'd fill the tank with 4 gallons to represent a 1/4th tank of a 16 gallon unit. Measure the height of the float to the bottom of the tank. Make a pedistal with the height of the same dimension. Now I can simply install a sending unit to the fixture as shown below, raise the float and install the 1/4 tank pedistal. Hook up the gauge sending wire to the sending unit, ground the fixture to the car's chassis and turn the key on. The needle will then go up to somewhere near 1/4 level. If the reading is off, I can simply tweak the sending unit's arm until I get a exact reading.

Whoola! All done tweaking.

Install the sending unit back into the car's tank and call it a day.

FuelSendingUnita.JPG
Click to expand...
 
Last edited by a moderator:
As I'm sure you realize, be very careful when working around a tank with gas in it or even if it was drained. A partially filled tank is more dangerous as compared to a full tank. If you don't have one yet, get a 5 gallon plastic gas can. Fill it with 4 gallons of fuel and mark the 4 gallon level on the outside of the can. This is really helpful when you have drained the tank and want to put exactly 4 gallons back in to check the 1/4 level accuracy. I also have a couple of those 5 gallon plastic buckets you buy at your local hardware stores, which are now dedicated only for gasoline and have lids for storage.

Nothing worse than needing to drain the tank when it is over half full and have nothing to store all that gas in. One of my buckets is marked with 1 gal, 2 gal, 3 gal, 4 gal markings.

When emptied wipe them clean, let them breathe for awhile and put the lids back on for clean storage. You'll be surprised as to how much crud the local gas pumps contributes to your tank besides just gas.

Another side note is do not disconnect the fuel line from the sending unit until you have fully drained the tank. With the sending unit being so low in the tank gas will start coming out if you have just 2 gallons in the tank. Since you have a drain plug, you will not encounter this problem but for those without a drain plug this becomes a real challenge.

And finally...................If you are willing to pay postage both ways, I'll be happy to let you borrow my fixture, when you are ready to take on this project. It would allow you to adjust the sending unit just one time without having to install it back into the tank until you are ready for the final install. I will provide instructions and a very easy to use sending unit lock ring removing tool. Once you try this tool, you'll want to buy one for your own.
 
Great information, and Yes, I'd like to use your fixture. It'll be a few weeks, it's not a pressing issue, now I know what I'm contending with and how to deal with it, no problems! ; ) My brother has a bunch of plastic 5 gallon buckets I can get that are clean, so I'll get those and mark them like you said. It'll be a few weeks~ I'll pm you giving you the necessary funds for shipping all at your conveniece!
thanks so much!
dne'


"cmayna" said:
As I'm sure you realize, be very careful when working around a tank with gas in it or even if it was drained. A partially filled tank is more dangerous as compared to a full tank. If you don't have one yet, get a 5 gallon plastic gas can. Fill it with 4 gallons of fuel and mark the 4 gallon level on the outside of the can. This is really helpful when you have drained the tank and want to put exactly 4 gallons back in to check the 1/4 level accuracy. I also have a couple of those 5 gallon plastic buckets you buy at your local hardware stores, which are now dedicated only for gasoline and have lids for storage.

Nothing worse than needing to drain the tank when it is over half full and have nothing to store all that gas in. One of my buckets is marked with 1 gal, 2 gal, 3 gal, 4 gal markings.

When emptied wipe them clean, let them breathe for awhile and put the lids back on for clean storage. You'll be surprised as to how much crud the local gas pumps contributes to your tank besides just gas.

Another side note is do not disconnect the fuel line from the sending unit until you have fully drained the tank. With the sending unit being so low in the tank gas will start coming out if you have just 2 gallons in the tank. Since you have a drain plug, you will not encounter this problem but for those without a drain plug this becomes a real challenge.

And finally...................If you are willing to pay postage both ways, I'll be happy to let you borrow my fixture, when you are ready to take on this project. It would allow you to adjust the sending unit just one time without having to install it back into the tank until you are ready for the final install. I will provide instructions and a very easy to use sending unit lock ring removing tool. Once you try this tool, you'll want to buy one for your own.
Click to expand...
 
cmayna,

Do you have a link to the tool you recommend for the fuel sending removal? (this easy to use tool sounds interesting)

Thanks,
Ed
 
You must log in or register to reply here.
Back
Top