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 =============================================================================================================== 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