Gas Gauge issue

I run VDO Guages and always have. I run a 17 Gal. Poly tank. On my '41, when I fill up it registers past full as it should. Once I use about 3 gallons the guage drops to 1/4 full and sits there. I know it is supposed to be a 240-33 Ohm sender etc, and I believe that is what I have. Any input appreciated.

 

Sounds like the float is hitting something ...possibly it is hanging up on a baffle or the side or the tank. How is the sending unit oriented in the tank?

 

Just to say I did it I would put an ohm meter on that sender to be sure it is what you believe it to be.
You can also try moving the sender arm through it's range slowly to see how the gauge reacts.
It will most likely require sender removal to perform those tests.

Pete

 

are you sure that a VDO fuel gauge uses a 240-33 ohm sender? i could be wrong ,but i believe it is different

 

To verify the gauge operation, go to a local electronics supply hose n' get yourself a couple of resistors as close to your full/empty 33-240 ohm values as ya' can...

Remove your sending unit feed wire n' ground it with one of the resistors in series to the gauge; if the gauge itself is workin' okay, it should give you your full/empty reading, dependin' on which resistor your usin'.

I don't recall if the values on the VDO tube sender are linear throughout its range from empty ta' full, but you could check what its readin' when it's actin' up...

 

Most senders in the plastic tanks are 90ohm.
Time to get out the ohmmeter and have a looksee. Headsup on a lot of those tanks when you unscrew the sending unit the nuts will fall into the tank, many are ***embled with the filler ***embly off the tank when they can reach inside the tank, some have nuts some have a ring that is threaded.

 

VDO actually also has a gauge that needs a 10-180 ohm sender, I'm wondering if I have a 240-33 sender and need the 10-180 which is a stewart Warner range.

 

VDO gauges are available for various ohm ranges. They are not just one range or they couldn't sell them for GM 90 ohm or Ford 70 ohm. Lots of variety, so need to check the sending unit as previously advised.

 

May not be this issue, but a shop had a problem with a sender (went thru 3) and still had problems, there seems to be some issues with the floats themselves. Maybe its the material used with todays solvent(gas). Personaly I would find a br*** float and solder it to the arm instead of that plastic float