Fuel Gauge Issue

[HeisenBob]

I topped the truck off with diesel because I'm concerned about the accuracy of the fuel gauge. It was at about 3/4 full and after I filled it up, the gauge it just reads way past full. The indicator is about a 1/2 a tank past full. Is this a sending unit issue or is the gauge messed up? Thanks.

 

[rmesgt]

This is typical of every CUCV I have ever driven while I was active. I cannot remember one where the fuel gauge stopped at full. With my trucks, I drove them to empty to learn where the fuel gauge needle is when the engine stops. The pro's with this plan is that you know (and when) you will run out of fuel. The con is that any gunk in the tank will definitely find it's way to the filter... Good Luck..!

 

[cruzer747]

hahahha... is it a chevy 2000 or older? Yes, this is an issue

if you were really persistent you COULD actually fix this. But I warn you it is not worth it.... easy way would be to rewind the resistor wire that the fuel sender wipes on. It is a 90ohm sending unit sou you could take it out, simulate full on the float and watch your gauge and compare it to your ohm readout on your dvm.... then check what it is at 0.... then at say every 20% of travel. (use a tape measure with the unit clamped still. Then look at your numbers and see how much you need to offset the amount of wire up or low (it will likely mean winding some wire above reachable as you will probably see actually 100-105ohms at full in actuality (hence the past full reading on gauge) and then most likely doing a gradual wind that went top fat to bottom thin. (some of this problem could be caused by the wires age increasing resistance which would offset the gauge high.... more resistance higher the gauge.... but I do not think that new sending units have actually solved this but I could be wrong.... hoping others could chime in here..?)

This would be VERY hard to do but it would be the right way to do it.

OR like mentioned above not how many miles you get till you start starving of fuel and always make sure you fill up and mark down odometer readings and fill up all the way and crunch the numbers on mpg like a lot of us do



IF I ever rewind one I will take very good notes and pics for a howto but this problem is extremely widespread. Even in the 90s and one 2001 chevy truck I have owned.


(i have not actually inspected my m1010 sending unit but the last 3 diesel sending units used a copper resistor wire wound over plastic iirc, there should be a thread on this, if I ever drop my fuel tank I will try and make the time to take this adventure)

 

[HeisenBob]

hahahha... is it a chevy 2000 or older? Yes, this is an issue

if you were really persistent you COULD actually fix this. But I warn you it is not worth it.... easy way would be to rewind the resistor wire that the fuel sender wipes on. It is a 90ohm sending unit sou you could take it out, simulate full on the float and watch your gauge and compare it to your ohm readout on your dvm.... then check what it is at 0.... then at say every 20% of travel. (use a tape measure with the unit clamped still. Then look at your numbers and see how much you need to offset the amount of wire up or low (it will likely mean winding some wire above reachable as you will probably see actually 100-105ohms at full in actuality (hence the past full reading on gauge) and then most likely doing a gradual wind that went top fat to bottom thin. (some of this problem could be caused by the wires age increasing resistance which would offset the gauge high.... more resistance higher the gauge.... but I do not think that new sending units have actually solved this but I could be wrong.... hoping others could chime in here..?)

This would be VERY hard to do but it would be the right way to do it.

OR like mentioned above not how many miles you get till you start starving of fuel and always make sure you fill up and mark down odometer readings and fill up all the way and crunch the numbers on mpg like a lot of us do



IF I ever rewind one I will take very good notes and pics for a howto but this problem is extremely widespread. Even in the 90s and one 2001 chevy truck I have owned.


(i have not actually inspected my m1010 sending unit but the last 3 diesel sending units used a copper resistor wire wound over plastic iirc, there should be a thread on this, if I ever drop my fuel tank I will try and make the time to take this adventure)

You lost me at "rewind the resistor wire". If it's a sending unit issue, is that in the tank? Wouldn't replacing the sending unit be the easiest fix? I currently can't check my mileage cause I'm also dealing with a non-operating speedometer.....

 

[cruzer747]

yes, it is in the tank. replacing it may make it better but unless someone says they have perfect range after doing so on theirs then it is not going to fix it.

here, worth a read. https://auto.howstuffworks.com/fuel-gauge1.htm

I would imagine that these are not much different than the chevy ones in my later trucks and the "resistor strip" is just some very fine copper wire wound around a pole. I would say if it bothers you, when the tank is full and the gauge is reading "way past full" disconnect the wire that goes to the gauge and measure resistance to ground. if it is much higher than 90 ohms than your gauge is doing its job. (you are probably seeing 100-110 ohms at full, doesn't take much)

Anyways, you can also install an aftermarket level sender for a fuel cell, that design is probably more accurate but I have never used one. Just drill a hole and get the right length sender for the depth... and take plenty of pics and post here

 

[Barrman]

If the gauge moves with fuel then it is about as good as the stock system ever was. 3/4 tank indicated should be considered no more than 1/2 tank of actual fuel left. 1/4 tank indicated means you will be walking soon. It will still run at E. Probably. But not on slopes or inclines and not for long.

 

[edpdx]

My 70's Chevy's all go past full- but I still let them get down to 1/8th tank without sweating finding a gas station. If in doubt... fill a jerry can and when you run out mark the lens.

 

[HeisenBob]

My 70's Chevy's all go past full- but I still let them get down to 1/8th tank without sweating finding a gas station. If in doubt... fill a jerry can and when you run out mark the lens.

As soon as I get the speedo gear in place and confirm the odometer and speedo are working, I can figure out how far I can go before it being an issue. I’m a little worried about the fuel tank and potential sludge from 35 years of buildup. The tank is far down the list right now.

 

[nyoffroad]

I guess you could rewind it but wouldn't it be easier to bend the float level rod? IIRC you just pull the assy. and guesstamate how much to bend it, what the worst that can happen the gauge will be off. Or disassemble the gauge cluster and pull off the needle and reinstall, I did that on something but not sure if a Chevy truck.

 

[Matt S]

I was having issues with my truck going past full and staying there for most of the tank. I found that the engine would cut out as the gauge was one tick away from empty. I replaced the sending unit (after trying to clean the connections) and the gauge works as I would expect it to.

 

[cruzer747]

I guess you could rewind it but wouldn't it be easier to bend the float level rod? IIRC you just pull the assy. and guesstamate how much to bend it, what the worst that can happen the gauge will be off. Or disassemble the gauge cluster and pull off the needle and reinstall, I did that on something but not sure if a Chevy truck.

not sure that would work but it could be worth a try, if you want it to read 90ohm at full and you bend the float upwards so the wiper is lower when full in relation to the float, then when the wiper would get to zero before the float travels all the way down. Wouldnt be too bad as you would likely be able to drive on E longer than normal.

If you got a 100 Ohm variable resistor you could easily test the gauge. I would not reset a needle on a gauge that was working properly out of principle but if that were part of the problem then why not!