[T3] calibrate fuel gauge

[Jim Adney]

On 21 Mar 2019 at 15:55, Daniel K. Du Vall wrote:

> Is there a way to calibrate a fuel gauge on a 72?
> Mine is off by the red zone both full and empty.
> Empty is the top of the red zone and full is the equally above the full mark.

I don't know if I've ever heard of this before. I've never actually come across 
it myself. It would probably be worthwhile to test it by applying appropriate 
resistances in place of the sender to make sure of where the problem 
actually is.

FYI, when full, the sender should measure about 5 Ohms. When empty it 
should measure about 95 Ohms.

I don't know of any way to recalibrate the gauge, but if the sender is the 
problem I should be able to fix it. If your sender is an aftermarket repop, I 
have good used OG VDO senders available. OG senders have VDO molded 
into the top flange. I've been sent a number of the Chinese repops for repair 
and I can assure you that they are not worth buying.

It's possible that you could adjust this by putting a suitable resistor in series 
with the sender. Adding ~10 Ohms might do the trick.

If it's the gauge that's at fault, I have good used ones, either the whole 
gauge or just the meter insert.

The gauges themselves are pretty odd inside. I've never figured out how 
they work, because they have 3 terminals outside and a couple of resistors 
inside in addition to the meter movement. I've never been bothered by this 
enough to try to figure out what they're doing. They usually just work, so they 
get ignored.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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