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What would cause a new VDO gas tank sending unit to make the gauge read full when the tank is empty?

Only thing changed was the sending unit. The old one stopped registering anything.

It is the correct gauge for the tank and car.

Thanks in advance. It probably is something obvious.

Bob 

     

       

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Two solutions:

A Porsche sender works well and doesn't bounce around too much. You can fine these (made in china) for about $30. An OEM sender will be about $100.

To be absolutely, positivity sure get a stick. With a pocket knife cut a number of notches in the length about 1" apart. Stick it in the filler and if it's comes out wet you've got gas. Many of the folks here have espoused this method in the past.

Reset the odometer when you fill up. Know what your burn rate is. I get about 200 miles on a 10 gallon tank before I get nervous.

When all else fails fly the numbers

It depends on your gauges.  VDO's standard is 10-180 Ohms, while old VW standard is 73-10 Ohms.  Mixing the senders incorrectly will make it read backwards and also not give an accurate full or empty when bent 180 degrees.  There have also been some oddball (non-VDO) Brazil gauges as well as some oddball China gauges with "custom" Ohms ranges that really don't match either of these but can be controlled with the above by setting the stops at the appropriate spot.

The thing I found about the stock arm is that the tank is roughly 7 1/2 inches deep where the sender is and the sender arm is much longer so it sits on the bottom of the tank for part of its swing.  When I drove away from Greg at VM the last things he said was don't trust the fuel gauge under 1/4 tank and the turn indicators don't cancel I did a lot of testing of the Centroid sender. I drained the tank till the guage read empty and looked inside with one of those scopes from Amazon.  The tank hadbetween 1/4 and1/2 gallon left below the sender around the outlet. I put 2 gallons back in and the VDO guage read 1/4 tank, I added another 2 1/2 gallons, 1/2 full, added 2 1/2 more guage read 3/4 and 10 gallons full. Now I know if the guage reads empty I've got about 5 miles left at least.

Being old school OCD, my gas gauge drove me nuts for the first year.  If I adjusted it for the proper “full” reading then it was way off at “empty”.  If I then re-adjusted it for “empty” it was way off at full (not to mention that it used to have that typical, half-gauge needle swing as gas sloshes around in the tank).  

Finally, I got tired of messing with it and set it so that when the needle hits empty and is still moving slightly off the bottom on a hard turn, I still have maybe a gallon of gas left down in there and can creep to the next gas station.  

I really don’t care about any reading north of 1/2 tank (and why should I? ) and it seems consistently accurate below 1/8 tank, so I live with it as part of an eccentric automobile. AND I have never run out of gas on the road!  That says something!

Since neither my odometer or gas gauge are accurate, I use this.

image

Fits perfectly between the frame rail and the body in front of the interior bulkhead. I pretty much top up the tank anytime I go for a ride and know I have about 150 miles before I have to worry. If I miscalculate, I have 5 gal to get me to the next service station.



The guy whips making my aluminum tank tells me he can order a tube sender like Wolfgang posted that will work with the VDO gauge.

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Last edited by dlearl476

I have a Centroid sender installed in my custom tank (actually 2 tanks cross-connected).  It works "ok".  I have custom shaped tanks, so the Centroid sender was the easiest straight-line solution. The gauge is bouncy when fuel sloshes back and forth in unbaffled tank.  But if the reason you want a fuel gauge is to warn you if getting low on gas, it does the job well enough.  I've had it for over 20 years, so it seems to last.

I replaced my VDO brazil gauges. The Tach was not working and the multi gauge lens broke. I bought Carey's special edition VDO gauges that he has made for him. They are fantastic. Speedometer is accurate by using a GPS module and doesn't jump around. The gas gauge also is steady and reads full at full and empty at empty. Also there is a red indicator light on the tach that I hooked up to my light switch that reminds me to turn of my driving lights. Could not be happier with them.

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Wow, I missed this whole thread, but it's just like the one we all wrote last year.

Or, was it the one from the year before that?

Could have been the 2016 one.

I still don't get it. Like Noel and Danny and a few others wrote, after 100 or 120 or 150 miles - or whatever your number is - stop for gas. You're going to want to get out of this car anyway after two or three hours.

The little bouncy toy display on the dash is just an ornament - it moves and lights up at night. It's there to entertain. It's kind of like those fake fender portholes on old Buicks - just a suggestion of something that is functional on other cars.

Watch your miles or just stop after two hours. You've got a phone that tells you when it's been two hours, right?

Don't worry, you'll be fine.

.

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