Sending unit recommendations

[baldessariclan]

Thanks guys! Fuel level sender testing not all that hard to replicate, if you want to try it yourself. I just drew lines at 1 inch intervals on a piece of cardboard, and cut a slot on one end so sender and its wire would fit in it:

Then I grounded the body (flange) of sender via a separate wire, turned on ignition, and marked where the sender arm sat, corresponding to fuel gauge needle positions — e.g.:

Etc.

Finally, I disconnected the sender from its wires, reconnected it to my multimeter, and recorded the resistance readings for those various arm positions, as shown in my earlier pics.

The results aren’t necessarily super-precise of course, but they should at least give a reasonable ballpark for what the sender’s resistance levels are at corresponding fuel tank levels.

Note that the fuel tank itself isn’t “uniform” in cross-section either. It’s got a lot more volume at top end of the tank, and a reduced volume area at bottom of tank. So the sender arm positions and resistance levels won’t be strictly linear either.
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1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[2type2]

All this info is great. The techniques for testing, the expected parameters, the possible tweaks and fixes....... But thr real question is:

After all these years, why is there not an accurate aftermarket drop-in eplacement that actually works?

Undoubtedly there is a market. I've whined about this before. I'm tired of writing down all my gas and mileage.At the very least it would be nice to be able toget a decent reasonably priced manual mileage counter for the dash!
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"A life of peace and happiness depends on your own gratefulness"

[viiking]

[viiking]

Here's one from CIP1 that looks like mine and is original VDO.

https://www2.cip1.com/vdo-221-012/?srsltid=AfmBOoo9hqbFQwY-mYyfdGYQxH8gGdrQy4F3-e_6jKNJo2oloSAde7zt
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[bugger-off]

[bugger-off]

Installed new VDO unit. Basically the same issue with the fuel gauge as with the previous sending unit.

So my next question is do I throw a new fuel gauge and vibrator at this thing? And, if I do, does the gauge need to be tweaked?

Should I just go back to filling the tank every two hundred miles? Definitely the easiest route to go.

[2type2]

I feel ya, my experience was the same -- all new stuff, no improvement. My '71 is way off, my '65 has inaccurate reading with mechanical sender also. Paper and pencil saves the day. My question is -- why is this still not fixed by the offering of an aftermarket IMPROVED part?

Usually an upgraded replacement gets created to fill the need
_________________
"A life of peace and happiness depends on your own gratefulness"

[heimlich]

[viiking]

I said this a few posts back. Have you actually measured the resistance that the gauge receives. If you have added high resistance in the wiring from the sender to the gauge for whatever reason, then you may get a premature and inaccurate low gauge reading (high resistance). It however does not explain why the tank is apparently reading full (low resistace). It appears that you have a number of sender units that are working correctly but the gauge is not receiving the correct information. Before you think of a new gauge and/or vibrator or wait for heimlich's solution you should check this. It would be a shame if you replace all the hardware only to find out there is some problem with the wiring.

[baldessariclan]

[bugger-off]

[baldessariclan]

[bugger-off]

So you are saying that the wires themselves need to be checked and NOT have the sending unit hooked up at the other end?

[baldessariclan]

Yes -- you tested the sender separately earlier, so you already know what its resistance values are, right? You just want to make sure you don't have a bunch of unintended resistance somewhere else in the system (e.g. bad/dirty connections, corroded wiring, etc.).
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[baldessariclan]

Another idea to consider -- at your next gas tank refill, might be helpful if you could take and post some pics of your fuel gauge reading and how many gallons it took to top off the tank. May help us to better figure out exactly where and how any "inconsistencies" are occurring...

E.g. here are some I took recently:

Tank refill with fuel gauge needle resting on the "R" line. Took 9.2 gallons to refill the (nominal) 10.5 gallon tank. So about 1.3 gallons should have been left in the tank when the needle was on the "R" line. Seems reasonable/consistent w/ the measurements and pics of gauge & sender I posted earlier:

And here' a tank refill with fuel gauge needle resting on the "1/4" line. Took 8.0 gallons to refill the (nominal) 10.5 gallon tank. So about 2.5 gallons should have been left in the tank when the needle was on the "1/4" line. Once again, seems reasonable/consistent w/ the measurements and pics of gauge & sender I posted earlier:

_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[bugger-off]

Yes, good idea, I will give that a shot. I probably have a couple gallons right now and the gauge is pegged all the way to the left, well below the "R". I'll fill and record/photograph the different positions.

[baldessariclan]

Sounds good! If you fill it slowly, you should be able to periodically pause, let needle stabilize for a minute, and then snap a pic of needle position and corresponding gallons filled at the "R" line, "1/4" line, "1/2" line, and finally the "1/1" (full) line.

From that last reading (i.e. gallons it took to get to tank completely full), should then be able to work backwards, computing how much fuel was in the tank at each of those points.
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[bugger-off]

I ran the tank down to damn near empty, maybe an eighth of a gallon. I put exactly three gallons in and the gauge needle did not move from being pegged all the way to the left, way past “R”. Bottomed-out. Didn’t budge at all. I didn’t take a pic, no reason to.

I added two more gallons for a total of five, damn near half tank. The needle barely moved.

I put in another 2.5 gallons, conceivably three quarters of a tank with only an 1/8 full gauge reading.

I then topped the tank off with 2.6 gallons (10.1 gallons total) giving me a tad below half tank.

I waited fifteen minutes between each addition of fuel for the needle to “catch up”.

These unacceptable readings from the new VDO sending unit are actually worse than those of the two cheap ones previously used. $60 for the VDO and $15 for the Chinese specials. Wow, screwed the pooch on that one!

So, yeah. Good times. I’ve had a few bugs and never had such inaccuracies. This has to be the gauge.

[viiking]

You have three possible causes that I see. The symptom is that you have a lower reading than you should across all of the readings. You don't show full at any time when the sender is fitted and the tank full of fuel.

1. The gauge or vibrator has failed.
2. You have a higher resistance than you should for a given level in the tank.
3. Someone has been in the gauge and actually bent the gauge needle.

The last one is unlikely but possible but I added it for completeness.

I've suggested you check the resistance in the wiring. I strongly urge you do it but it looks like you haven't done so. There are a number of posts on the SAMBA where people have had issues and have urged the cleaning of the connections or the complete replacement of the wire from the tank to the gauge.

If it were me I would:

1. Check the wire resistance.
2. If higher than expected run a new temporary line from the sender to the gauge. Do this after checking the resistance of the temporary line is very close to zero. If this improves the operation of the gauge, you have your solution.
3. If the resistance proves ok from 1, then and only then start replacing your gauge. Better still see if someone can lend you a known functioning gauge.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[bugger-off]

I have checked the resistance in the wire and it is okay. I also cleaned all of the connections and dabbed Stabilant 22 on them.

No one has messed with the gauge. When I acquired the vehicle five years ago the gauge was working properly. After driving it for about a year, the gauge evidently stuck at 1/2 full-- I wasn't paying attention to the gauge OR the miles I had driven because I ran out of gas.

I then replaced the sending unit because of the erroneous gauge reading and the gauge moved off of half but I have had issues with accuracy ever since.

I have to believe the gauge has to be faulty.