Fuel gauge gremlin.

-
1968FormulaS340

1968FormulaS340

Well-Known Member
Joined
Aug 24, 2005
Messages
11,394
Reaction score
702
Location
St. Helens Oregon
Fuel gauge works fine from full to half a tank. Once it reaches the half tank level it wants to drop to empty.

On a refill it goes back to full and works fine again until I run about a half tank out.

I have cleaned all associated connections. What's your best guess? New sender time?
 
Sending unit in the tank is bad/broken.
This happens when the wire wrapped around a little board gets worn through, and interestingly enough it usually happens first in an area of the sender that has the most use on it.
In other words, if a person generally only fills the tank half way or less the sender wears out in that area first.
Check out this pic where the wire is wrapped and the metal arm slides up and down.
When that wire gets a break (worn through) in it, the sender quits or only works in the area that the wire isn't worn through or broken.

There is a little more to it than that, but I just told you the part that matters to your problem.

fuel2.jpg
 
My best guess... There is already a aftermarket sender in there. Those are linear in resistance so they don't function like OEM which was non linear. In every case, The sender is the first look simply because is a lot easier to R&R. Then R&R it again to bend on the float arm, whatever in attempt to make it more accurate at the gauge. If all else fails, R&R the inst' panel to have the gauge rebuilt could cure it or at least help to some degree. There is a vendor out there who rebuilds the OEM senders but you would have to first have that part.
 
RedFish said:
My best guess... There is already a aftermarket sender in there. Those are linear in resistance so they don't function like OEM which was non linear. In every case, The sender is the first look simply because is a lot easier to R&R. Then R&R it again to bend on the float arm, whatever in attempt to make it more accurate at the gauge. If all else fails, R&R the inst' panel to have the gauge rebuilt could cure it or at least help to some degree. There is a vendor out there who rebuilds the OEM senders but you would have to first have that part.
Click to expand...


Great thing about being friends with the previous owner. I can tell you this is the same sender that was in it as far back as 1979.
 
1968FormulaS340 said:
Any recommendations on a quality replacement or will a trip to NAPA take care of it?
Click to expand...

Napa, Autozone, Rock Auto, or about anywhere has them, but that's not the problem.
The problem is that no matter where you get it from they almost never read correctly again due to manufacturing tolerances and those short little people getting involved in it.:D

When I first replaced mine it was the exact part called for but afterwards my gauge would only go to about 2/3 full when the tank was full, and then take a long time to drop to the half mark.
Once it read below half it went down fairly normal to empty.
This was supposed to be exactly matched to the OE gauge but it sure wasn't.

I ended up replacing the gauge with an aftermarket unit rated for the exact same specs as the sender and everything got closer.
They also make a matching tool that is an electronic device that allows you to match the sender and the gauge.
For example, you put 3.25 gallons in a 13 gallon tank and set the matching tool to 1/4 tank.
Then you put another 3.25 gallons in and set the tool to 1/2 a tank and so on.

On rare occasions you will replace the sender and it reads correctly.
 
OH, and save your OE lock ring when you take the sender out because the new ones are thinner and don't seal nearly as well if at all.
 
OK, In any sender is a scrubber contact moving along a resistor wire. It could be that the hinge point or something has worn allowing the contact to leave the wire around the half tank point. This open condition yields no needle movement at all at switch on. If the sender is always closed, minimum resistance would generate some needle movement at switch on, up to about the empty hash mark.
More often that contact wears to a hook shape and hangs to the resistor wire , thus a fixed gauge reading regardless of fuel level. So the song remains the same, pull the sender first and lets have a look at it. Good luck.
 
Last edited:
I should have mentioned, this is something that started this summer. It had been working fine for the 14 years I have owned it.
 
You must log in or register to reply here.
-

Back
Top