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Amskeptic
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 Posted: Mon Jun 11, 2018 10:35 pm Post subject: Late Bay New Fuel Gauge Senders And Their Readings |
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I have run across many people recently who are not happy with their new fuel gauge senders. A common complaint is that the new sender only displays half full when the tank is actually filled up. Another increasingly common scenario is that the gauge plummets rapidly towards reserve when there is still plenty of gas left in the tank.
SO . . . look at the gauge. It is not linear. From full to half takes only 1/3 the travel. Then, 1/2 to below reserve takes 2/3 the distance.
We know that a full tank should yield a sensor reading of 10 ohms.
An empty tank should yield a reading of 75 ohms.
The gauge needle is linear. A half tank *reading* on the gauge should occur by around 25 ohms, then we have a long trip to empty from there.
It is the SENDER that gives us a progressively fasterr descent as the fuel level drops.
Here is a factory sender. Ignore the burnt up mess, please. The small end is the full side. Each loop slowly adds resistance, and the heater slowly cools and allows the needle to move lazily towards 1/2. Then the loops get bigger and each loop causes a larger increase in resistance and the gauge moves more quickly towards empty.
You are viewing the "variable resistor" from the "front of the bus" back. The lever/float goes up to the right in this photograph, which is actually to the left when installed in the tank. The short end of the "variable resistor" is toward full.
Does anyone have a new sender sitting around? I was thinking, the above symptoms could occur if:
a) the new sender has a non-progressive "variable resistor"
b) the new sender has a progressive "variable resistor" installed backwards
I'd like to resolve this.
Colin
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aerosurfer
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| Posted: Tue Jun 12, 2018 7:28 am Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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Can’t exactly help with your request, but I was under the impression the float itself was also one of the main problems with the new senders, they don’t remain sealed and fill up with gas and sink a bit below the actual level....
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Amskeptic
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Joined: October 18, 2002
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| Posted: Tue Jun 12, 2018 9:54 am Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| aerosurfer wrote: |
| Can’t exactly help with your request, but I was under the impression the float itself was also one of the main problems with the new senders, they don’t remain sealed and fill up with gas and sink a bit below the actual level.... |
That is an issue, yes, but different than this request. I have been informed by one person so far that indeed their new sender is a simple square card with wire wrapped around it, thus the progressive nature of the gauge is bodged to all heck.
Colin
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furgo
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| Posted: Tue Jun 12, 2018 11:18 am Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| Amskeptic wrote: |
| [...] their new sender is a simple square card with wire wrapped around it, thus the progressive nature of the gauge is bodged to all heck. |
It might be useful to see a picture showing how their wire is wound.
I'm sure I'm not saying something that you don't already know, but that the shape of the support is square/rectangular does not necessarily mean that the wire loops are not packed progressively tighter towards one end to achieve the non-linear resistance output.
This is a picture of a '76 sender showing this. I'm not sure if it was factory-installed, but it's an original VDO part with the VW part number.
A while ago, I documented what I measured on mine with some charts and diagrams. It would be interesting to see if the resistance curve of the sender with the necked board is the same.
https://www.thesamba.com/vw/forum/viewtopic.php?t=693930
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Last edited by furgo on Wed Jun 13, 2018 1:16 am; edited 1 time in total |
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busdaddy
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| Posted: Tue Jun 12, 2018 12:20 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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I can't recall seeing the necked board in any OG senders I've been in, they were all rectangular like Furgo's (although some were mighty scorched).
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Tcash
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| Posted: Tue Jun 12, 2018 1:24 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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If the board or the windings are not centered on the fulcrum this could account for the movement not being equal.
As far as the rapid change in readings in service. The windings, a sticky or jumpy float could be the cause.
Does it have a contact spring?
HOW TO: Revive your fuel gauge sender for $1 FAQ
https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0
Good luck
Tcash |
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Amskeptic
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| Posted: Wed Jun 13, 2018 10:44 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| furgo wrote: |
the shape of the support is square/rectangular does not necessarily mean that the wire loops are not packed progressively tighter towards one end to achieve the non-linear resistance output.
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True. I am trying to track down the whys and wherefores of so many irritated people and their irritating fuel gauges.
Your chart shows the progression nicely. 11 ohms takes you from full to half, another 12 ohms takes you just from 1/2 to 1/4 and 1/4 to justreserve is even more.
Sure, a progressively wound board would do exactly the same thing as my board (before I killed it), but it is harder on the wires under the wiper!
Colin
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SGKent 
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| Posted: Thu Jun 14, 2018 7:37 am Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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I've posted on this before. The original floats in late T2b were flat topped with the arm thru their middle. That allowed them to ride higher for any given fuel level. The new ones have a round float with metal that goes beyond them so they don't wear thru hitting the tank top. The replacement senders also work in some other VW models - they weren't calibrated for bays. With the tank out put the sender in and hook it up. Read the number with the arm all the way down. Use a wooden yard stick thru the fill opening to raise the float to the top. Read the gauge. Bend the arm to adjust. Do it again. When you are satisfied with the results you can bend the stop on the gauge in the down position if you want to set the downside. That is how I fixed mine and it reads 1/2 at 1/2, 3/4 at 3/4, full at full, and on reserve when it is on reserve.
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Whaanga
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| Posted: Thu Jun 14, 2018 4:54 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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I installed a new sender from Bus Depot a year ago and it works consistently.
The only issue I'm having is that when full, the gauge reads at 7/8's. I realize this my comment is less empirical than Colin's original post
but wanted to report that mine is working quite well.
Jeff
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SGKent
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| Posted: Thu Jun 14, 2018 5:10 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| Whaanga wrote: |
I installed a new sender from Bus Depot a year ago and it works consistently.
The only issue I'm having is that when full, the gauge reads at 7/8's. I realize this my comment is less empirical than Colin's original post
but wanted to report that mine is working quite well.
Jeff |
yes - you have to adjust the arm for it to read right.
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busdaddy
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| Posted: Thu Jun 14, 2018 5:20 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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I retract my previous statement about never seeing one of those necked boards, I just encountered one in a 74 Superbeetle today.
The new replacement "hecho in Mexico" sender was trash so I resurrected the OG unit, I never opened up the new one to look at the windings.
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rusty busty
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Location: Vancouver BC
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| Posted: Thu Jun 14, 2018 8:30 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| Whaanga wrote: |
I installed a new sender from Bus Depot a year ago and it works consistently.
The only issue I'm having is that when full, the gauge reads at 7/8's. I realize this my comment is less empirical than Colin's original post
but wanted to report that mine is working quite well.
Jeff |
I wish I were having that problem instead.
I installed a new sender a year ago also. It works consistently. When it's full it reads exactly full, but when it reads 1/4 full it actually means that I'm out of gas and I'd better start walking. Oh shit where was that jerry can again?
I wish it were accurate when its empty instead of when it's full. 
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SGKent
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| Posted: Fri Jun 15, 2018 8:47 am Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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make sure that the sender stop isn't holding the arm from falling all the way.
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rusty busty
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| Posted: Fri Jun 15, 2018 4:38 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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| SGKent wrote: |
| make sure that the sender stop isn't holding the arm from falling all the way. |
It doesn't seem like it's getting hung up. It goes down steadily and evenly until it hits 1/4 tank or a bit more sometimes, then I'm walking.
I plan to have the engine out in the next few weeks sometime to address a leaking flywheel seal. I'll pull the firewall and have a look at the sender at that time. If it looks ok I might just give the arm a bit of a tweak.
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Tcash
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| Posted: Fri Jun 15, 2018 6:40 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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If you got it out, don't tweet the arm. Tweet the stop the arm rest against.
Make sure the sender is installed perpendicular to the length of the tank and not hitting on the sides. |
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rusty busty
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| Posted: Tue Jun 19, 2018 9:28 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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Great. My bus has overheard me complaining about the fuel gauge not going to empty, so now the fuel gauge has gone to empty and stayed there. I'm assuming that the float is no longer floating.
So I got less than a year from the new sender. 
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DougB
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| Posted: Tue Feb 26, 2019 5:53 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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You’re lucky...the new one I just bought from Bus Depot leaked gas where the plastic insulator meets the top cap from the first minute it was installed. Sure, I know how much gas is in there, but the resulting fumes make me nauseous. 
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chazz79
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| Posted: Tue Feb 26, 2019 7:22 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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So what would be the best sender to buy? I have a new tank going in and would love to have a proper working gauge for once.
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busdaddy
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| Posted: Tue Feb 26, 2019 7:31 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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What's wrong with yours?, unless it's melted or rusted so badly the arm broke off the best cure is to rewind the OG one.
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Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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DougB
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| Posted: Tue Feb 26, 2019 8:29 pm Post subject: Re: Late Bay New Fuel Gauge Senders And Their Readings |
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Oh, I didn’t know you could rewind them. I’ll have to find that thread...I still have all the parts, but the wire is severed. Interesting that my gauge crapped out at the same time, too, but luckily I had a spare.
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