Fuel gauge swing while driving

[mopar_earl]

Hello,

My fuel gauge moves a lot while driving. While parked its steady. When the tank is full, the gauge will move from full to half and back as I drive and make turns. At half a tank it moves from half mark to the 1/4 mark. Not sure if this is correct for old cars or if my sending unit needs cleaned or replaced. When I whip the wheel back and fourth the gauge really goes wild. That tells me the float swing is to the left or right.

Thanks,

Earl

[55 Fargo]

This could be a bad ground, and/or poor connections.

Is this a 2 wire or 1 wire sender unit.

Start with checking your connections, at the gauge and at the tank sender unit.

A faulty fuel sender unit could make things swing or false reading, possibly the windings in the rheostat are old and worn..

See you have a 52, so 1 wire, easy to work with, tank has no baffles, so fuel can move the sender float a lot too.

Testing, on yur gauge, if you take off the wire to the fuel tank sender, and or short it to ground, the gaue will read full and be pinned fast. That tells you the gauge is fine, or working.

I would check out connections and even make a dedicated ground wire for the gas tank to the frame, nice #8 or #10 gauge wire...

[mopar_earl]

Thanks, I just need to confirm if the movement is normal or not. I don't like to fix things that aren't broke. Lol but yes I do know how to make proper grounds and connections. I know mondern fuel gauges are buffered so they don't move around. I'm haven't been around cars this old to know if what I'm seeing is normal or an issue.

Earl

[Young Ed]

I believe the 49-52 gauges are direct read. So if you are sloshing a lot you will see a lot of movement. The 50 and 51s I've driven were all like that. I think the 54 might be as well.

[TodFitch]

I believe the 49-52 gauges are direct read. So if you are sloshing a lot you will see a lot of movement. The 50 and 51s I've driven were all like that. I think the 54 might be as well.

Agree, I've never heard of damping being done in the sender, so if there are no baffles in the tank the sender will be reporting lots of movement.

 

It could be that the damping mechanism in the dash unit is faulty. Or, more likely, the car never came with it and what you are seeing is normal.

 

The two wire systems from the late 30s to 48 are inherently damped as they work on temperature in the dash unit which takes a little time to change. But my earlier car with a one wire sender shows every slosh in the tank. Just don't corner as hard and you'll not notice it as much.

[ptwothree]

Is this something that just started to happen??  Is your car 6 or 12 volt?

[mopar_earl]

Is this something that just started to happen?? Is your car 6 or 12 volt?

Own the car for 16 years. Drive it twice 16 years ago. This is the first its had a fill up since I owned it. So no idea what the gauge did 16 years ago lol.

Car is 6v positive ground.

Earl

[mopar_earl]

Sounds like it maybe normal. I will see how it does. About due to refill the tank, will see how accurate it is.

Earl

[ptwothree]

According to my book, the gauge has two windings; one is externally grounded to the tank sender and reads directly off the sender.  The other one is internally grounded and provides a constant pull on the needle towards empty.

 

Sounds like that is your problem.  The internally grounded winding is open so there is no damping taking place.  The needle, therefore, is reacting directly to what the tank sender is doing.

[greg g]

Try running a separate ground wire from one of the screws holding the sender to the tank and one of the screws holding the access cover to the trunk.  Also you might want to run a ground strap from the body to the engine or frame. (this is a good idea for older 6V systems.  It doesn't cost much and can improve the performance of any and all body mounted electrical lamps and devices.)  I had a similar problem with mine and found that the defroster duct had fallen of the drivers side diffuser, and would under certain car motions flop around up under the dash.  It would sometimes cause an inadvertent ground path through the stiffening wire whn it contacted one of the terminal posts on the fuel gauge.

[mopar_earl]

I have added a ground strap from the engine to the body. That brighten my lights all up. I do plan to run a ground strap from the engine to the frame.

Filled tank up. The gauge appears to be accurate. When completely full the gauge holds steady. I will add a ground to the sending unit and the dash/gauge.

Earl

[greg g]

don't mess with the gauge, just make sure nothing around it is flopping around that might provide a ground path where one is not wanted.

[mopar_earl]

After a couple fill ups and what my manual says, I believe it's the nature of the beast. The manual basically says it reads in real time so it will move as the fuel moves around in the tank. Just didn't expect it to move as much as it does. But its accuracy is good. You just need to be stopped or on smooth road to get an accurate gauge reading. Lol

Earl

[Plymouthy Adams]

by the very explanation in my book..you will find it to be quite the opposite....the system by design is slow to react and thus a very solid needle..you may have a faulty wiper arm or deformed resistor block in the sender housing...causing errractic action when the wiper and resistor are not making proper solid contact with on another

[mopar_earl]

by the very explanation in my book..you will find it to be quite the opposite....the system by design is slow to react and thus a very solid needle..you may have a faulty wiper arm or deformed resistor block in the sender housing...causing errractic action when the wiper and resistor are not making proper solid contact with on another

Not for my year car. It is direct read. Unless the manual is wrong. Lol I will take a pic and post.

Earl

[mopar_earl]

From my manual. 1949 to 1952 Dodge cars.

Earl

[Plymouthy Adams]

ok...later car one wire...yet..the movement is still a slow read...but not as slow as the earlier two wire...your unit as a one wire is more susceptible to the erratic conditions of the wiper and resistor....the wiper arm as it is moved by sloshing of fuel could cause the wiper on the resistor to drop in and out of contact

[mopar_earl]

I'm sure after 60 years the sending unit is badly worn. For now it works and accurate when the fuel isn't sloshing. I will replace it after I get the priorities taken care of or it stops working.

Are the aftermarket sending units OK or would I need an NOS unit?

Earl

[Plymouthy Adams]

your unit can be a modern device...in your post of the picture..your resistance values are shown..that is what you match your new sender against....

[ptwothree]

According to my book, the gauge has two windings; one is externally grounded to the tank sender and reads directly off the sender.  The other one is internally grounded and provides a constant pull on the needle towards empty.

 

Sounds like that is your problem.  The internally grounded winding is open so there is no damping taking place.  The needle, therefore, is reacting directly to what the tank sender is doing.

 

You either need to replace the gauge or repair what you have.....

[TodFitch]

A number of people are saying its broken, but my reading of the manual section posted the operation seems normal. If it ain't broke, don't fix it.

 

Interesting to read in the manual section posted that the lack of contacts opening and closing (like in the two wire thermostatic setup) means that there is no interference with radio reception. I wonder if that is the reason they dropped the two wire sender setup.

[mopar_earl]

It's definitely not broken as it works and is accurate. Is it suppose to move around, yes. The manual clearly states that. Is it suppose to swing like Tarzan? Not sure, I'd say not. The sending unit would wear out over time. The gauge, other than the needle swinging on a pin, there is nothing to wear out.

I'm not going to do anything about it. Like I said it will get put on the list as a low priority as I have tons of money needed else where, unless it craps out.

When I get the free time and feel like it, I will pull the sending unit and work the float slowly and see if the gauge goes crazy as it's moved. If it does, the sending is worn on the pot. Much like a slot car trigger wearing out. Lol

If and when I figure out anything is actually wrong, I will post it.

Earl

[Plymouthy Adams]

if is normal slosh...then you would equally move high and low...if falling to the low end and back to a set position without ever going higher...I's still say look to erratic wiper contact...

[meadowbrook]

My '50 has a mid 70's Jeep fuel tank with a 1 wire sender. Despite the fact my vehicle is still 6V +gnd, my gauge is pretty accurate but it does swing quite a bit also.

 

I was used to it since my '65 VW Karmann Ghia also swings wildly, but that one is completely mechanical, a thin cable connects the needle to the float.  .

 

What I find amazing is that the tank does not explode with the electric system. I mean you have a wiper conducting current sliding across several wound wires. Wouldn't that occasionally cause a spark?

[Plymouthy Adams]

fuel vapors displace the oxygen to the point there is not enough air to cause an explosion..