Roger,

Sounds like the sender unit is at fault - the gauge would probably not behave
with these symptoms. The sender is a variable resister (potentiometer) with a
lever arm and float assembly - the gauge indicates full deflection (full tank)
when the sender is at its lowest resistance - the upshot is that it sounds
like the resistance element in the sender has an open circuit around the
mid-travel point. You can verify that the gauge is not at fault through a
procedure in the bently manual where you wire series resistances inplace of
the sender (gauge to resistor to ground)
while checking the needle deflection. Symtomatically, yours REALLY soundslike
the sender - I just replaced mine in my 80 Vanagon - had similar but not
identical behavior (my sender was partially shorted - not open).

Isn't your tank back just in front of the engine - This would have been an
awful job on my old 68 bus (engine out first), but I'm not recalling how the
tank is mounted in a 79.

Regards,

Ken Stich

OBTW - sender is $39.95 from Bus Depot - includes o-ring seal
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Roger Brant wrote:
>
> The gas gauge on my '79 Westy has suddenly taken on strange behaviour.  It
> reads full upon fill-up, but right around the half-way mark, it soon reads
> way below empty (like right on the pin)  I haven't actually observed it
> drop, being too busy driving, but refilling has proven that it happens when
> the tank is roughly half-empty (half-full, if you're an optimist!)
>
> What's the explanation for this, and how easy is it to fix?  I'm having the
> engine out for a major overhaul soon, so maybe that's the time for this
> problem, too?
>
> Thanks, all.
>
> Roger