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Fuel gauge help
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Dougster43
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PostPosted: Mon Aug 06, 2018 1:21 pm    Post subject: Fuel gauge help Reply with quote

Hoping for some fuel gauge system help. I searched through the forum but didn't find anything that was quite the same.

I have replaced the sending unit, fuel gauge, vibrator, and all wiring on my 73 (Aftermarket - the gauge and sending unit are Classic Line and the vibrator is from Thing Parts).

The gas gauge only reads just above half with a full tank. Verified with 2 different sending units. If I connect the sending unit wire directly to ground then the fuel gauge will read full.

Below about a half tank the gauge seems to read fine all the way down to empty.

Has anyone seen this before? I'm open to suggestions on what to try next.
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sdwalter
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PostPosted: Tue Aug 07, 2018 12:37 am    Post subject: Re: Fuel gauge help Reply with quote

Check the ground between the sending unit and gas tank and gas tank to body. An easy way to check if this is it, is to run a wire between one of the sender screws and the ground tabs on the body behind the headlights.
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74 Thing
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PostPosted: Tue Aug 07, 2018 7:11 am    Post subject: Re: Fuel gauge help Reply with quote

Fuel sender in the tank? Yours is aftermarket so I do not know if the quality is there. https://www.thesamba.com/vw/forum/viewtopic.php?t=655121&highlight=fuel+sender+repair
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JayC
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PostPosted: Tue Aug 07, 2018 9:00 am    Post subject: Re: Fuel gauge help Reply with quote

I have been fighting this same issue since day one with my thing. Even after the restoration, I have not been able to get it to read full. Sorry, wish I had a better answer. I have tried multiple senders, gauges and vibrators with no luck.

I am sure it has to be something in the wiring, but I can't find it.

jay
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Semper_Dad
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PostPosted: Tue Aug 07, 2018 7:11 pm    Post subject: Re: Fuel gauge help Reply with quote

Here's a good read on fuel gauge mechanics and diagnostics

http://www.nls.net/mp/volks/htm/fuel_ga.htm
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Dougster43
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PostPosted: Wed Aug 08, 2018 7:37 am    Post subject: Re: Fuel gauge help Reply with quote

Thanks. I tried the additional ground wire to the sending unit last night but that didn’t change anything. The gauge just seems to reading about half of what it should -,was reading just above a 1/4 tank on the gauge and took 5.5 gallons of fuel to fill it up.
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wbailey2112
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PostPosted: Wed Aug 08, 2018 10:52 am    Post subject: Re: Fuel gauge help Reply with quote

Any thoughts as to if this might just be a mechanical issue and not an electrical issue? You may want to check the float and the arm from the sender to the float as the possible culprit. I would think that there might be an opportunity there to make an adjustment by way of strategically bending the arm (think of the old days when you could bend the arm from the ballcock to the ball float in your toilet tank to adjust the water cut-off and therefore the water level in the tank).

My fuel gauge works throughout the range shown on the dial however it has never been all that accurate or linear in its operation.
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blsthng
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PostPosted: Wed Aug 08, 2018 2:18 pm    Post subject: Re: Fuel gauge help Reply with quote

Even though it is a new unit, make sure the float is not full of gas.
You can also test it out of the tank
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helowrench
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PostPosted: Wed Aug 08, 2018 3:27 pm    Post subject: Re: Fuel gauge help Reply with quote

http://www.midsouthvw.com/TechTips/tech_tip_FuelGauge.htm
This is the same system.
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7Thng3
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PostPosted: Mon Apr 15, 2019 5:35 pm    Post subject: Re: Fuel gauge help Reply with quote

This might be a stupid question.... I have owned my Thing for 10 years and the fuel gauge has never worked right. I thought it might be the vibrator, after looking at it finally don't laugh, I found that their is no 12v hooked up. I can't find any loose wire anywhere, I'm planning to run a new 12v wire, where should I run it from. Thanks for your help
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obus Premium Member
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PostPosted: Mon Apr 15, 2019 6:30 pm    Post subject: Re: Fuel gauge help Reply with quote

https://www.thesamba.com/vw/archives/info/wiringthing.php


if you didn't see this yet ^^^^
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7Thng3
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PostPosted: Mon Apr 15, 2019 7:02 pm    Post subject: Re: Fuel gauge help Reply with quote

Thanks!!! I have seen this, I will open it back up to see if I have missed something. It's fairly organized, not a big rats nest. The gauge will show empty for a time, then go to a half tank, then back to empty.I will get this to work one way or another.
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Blue69Baja
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PostPosted: Thu Mar 12, 2020 3:50 pm    Post subject: Re: Fuel gauge help Reply with quote

If you are still having this issue check this thread..

https://www.thesamba.com/vw/forum/viewtopic.php?t=732561&highlight=sender

Jim
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Dougster43
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PostPosted: Sun Jun 20, 2021 3:00 pm    Post subject: Re: Fuel gauge help Reply with quote

So I finally got far enough down my list to dig into my fuel gauge issue.

By trying some of the items mentioned previously, I used a jumper wire and determined that the gauge would read full if the wire at the sending unit was connected to a good ground. That means that the issue was with the gauge sending unit in the tank.

During my restoration, I had found a VDO brand NOS sender, but the gauge was still only reading half full with a full tank and would go down from there to empty as the gas was used up. I don't know how accurate it was on the empty reading but at least it gave some kind of indication.

I removed the sending unit from the fuel tank. and swung the arm back and forth. I immediately noticed 2 things:

1. There are 2 tabs that stick down from the mounting plate of the sending unit that provide a "stop" at either end of the swing arm travel. One of those was bent in slightly which was limiting the range that the arm could swing. I straightened that out and then pushed the arm with the float to the maximum "high" position. (Note that I had run a jumper wire to the sending unit body to make sure it was getting a good ground). Once the arm was at the highest swing, the fuel gauge did read full, so that was good news.

2. With the sending unit still outside of the tank and the arm at the highest travel, I noticed that the position of the float was actually about 2 inches higher than the mounting plate for the sending unit. So that meant there was no way the gauge could ever read full since the arm would hit the top of the fuel tank before it ever got to the highest travel limit. (Think about a toilet float where the float would hit against the top of the tank before it shut off.) The obvious answer was that the arm needed to be bent to allow for the maximum range of swing.

So I measured the depth of the fuel tank to be about 8 inches. I noticed that at the bottom of the arm swing, the float was only sitting about 6 inches below the mounting plate. Using a tape measure, I bent the arm such that the float was sitting even with where the top of the tank would be in the highest position, and then verified that it was sitting about 8" down from that in the lowest position, which it was.

I put the sending unit back in the tank and headed to the gas station. After filling the tank, the gauge now reads full. I'll keep an eye on the miles to see how the gauge works as the tank level drops, but I believe it will work now. The question now is how accurate is the "empty" reading.

Hope this helps, it was really a pretty easy fix.
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Blue69Baja
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PostPosted: Sun Jun 20, 2021 3:12 pm    Post subject: Re: Fuel gauge help Reply with quote

Excellent work Dougster!

If you have a DVM you can measure the resistance of the sender when the gauge reads 1/2 tank.. It should be around 21 ohms...
Drive some more down to 1/4.... and measure the resistance again.
It should read about 33 ohms.

To measure the resistance you must disconnect the sender signal wire, the center one to get a correct measurement:

Although this sender is for a type 2 the resistances are the same for each fuel level!

Image may have been reduced in size. Click image to view fullscreen.


Jim
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Dougster43
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PostPosted: Mon Jun 21, 2021 6:17 am    Post subject: Re: Fuel gauge help Reply with quote

Great information, Jim - thanks for sharing!!
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mondshine
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PostPosted: Mon Jun 21, 2021 7:57 am    Post subject: Re: Fuel gauge help Reply with quote

In the many ACVW's I have owned, I have never had one with a fuel gauge that read anything close to linear. For example, my current Thing will read over 3/4 tank after 100 miles, then ZOOM! ... down to the red in the next 90 miles.

When I get a new (to me) VW, I drain the tank and pour in a measured two gallons of gas. Then I drive to the corner gas station and add 2 gallons at a time, pausing to make a note of the gauge reading. That way, I have some idea of where the gauge needle is indicating 2-4-6-8 gallons, and full.

On road trips, I do carry a 2.5 gallon NATO safety can, just in case I get stupid or careless.

Good luck, Mondshine
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Dougster43
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PostPosted: Mon Jul 05, 2021 5:01 pm    Post subject: Re: Fuel gauge help Reply with quote

So here is my report out so far - the gauge seemed to perform pretty linear and was down to reading 1/4 tank when I filled up today. It took 7.2 gallons to fill the tank up into the filler neck after which the gauge read full again. Just FYI I am averaging around 17.4 MPG over the last 2 fill ups.

I really like Mondshine's idea of draining the tank and then adding 2 gallons at a time. I think I'll put that on my list. I'd like to know what the tank reads with only 2 gallons in it so I can feel a little more comfortable to rely on the gauge, but so far so good!
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CanStan
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PostPosted: Tue Jul 06, 2021 8:39 am    Post subject: Re: Fuel gauge help Reply with quote

mondshine wrote:
In the many ACVW's I have owned, I have never had one with a fuel gauge that read anything close to linear. For example, my current Thing will read over 3/4 tank after 100 miles, then ZOOM! ... down to the red in the next 90 miles.


I don't think VW has figured out this issue 50 years later. I have a newer Golf Wagon and the gauge pegs to full for the first 1/4 tank. When it gets down to half on the gauge, it's actually more like 1/4 of the fuel left at best.

The shape of the Beetle and Thing tanks is not even all the way down. It's wide at the top, and narrows toward the bottom. So, for example, if it burns 1 gallon of fuel from a full tank, the float might drop 1". But when you burn 1 gallon of fuel from a near empty tank, the float might drop 3". Maybe when the OG senders were new, the resistance values accounted for this variation, but I'm betting even slight corrosion, worn parts, or the lower quality of aftermarket parts makes it impossible to get anything super accurate.
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mondshine
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PostPosted: Tue Jul 06, 2021 11:37 am    Post subject: Re: Fuel gauge help Reply with quote

CanStan-

Our modern VW's ('17 Passat and '16 Golf Sportwagen) have very accurate fuel gauges. I suspect they are controlled by one of the 15+ ECU's. They calculate consumption rate, miles to empty, even the additional consumption from active accessories, like heated seats, AC, rear defrost, etc. Cruising at a constant speed on the freeway, you can open the windows and watch the consumption rate climb due to turbulence/drag.

Modern cars are pretty amazing, but it's like owning an amazing refrigerator; after a few days, the excitement fades away.

But a road trip in a Thing... Now that's a whole different ball game!
The thrill is still there (for me, at least) after 40+ years in the Thingdom.

My "2 gallons at a time" method of guesstimating "miles to empty" is "close enough to play jazz" for my 48 year old jalopy.

On road trips, I usually stop for gas between 1/4 and red (I am an old guy, and don't mind getting out of the car to walk around a little every now and again anyway). I do carry a couple of gallons of extra gas on road trips just in case.

Good luck, Mondshine
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