dual tanks, where's all my gas going?

[monster man]

so I've filled my dual tanks twice now, and each time I get to the bottom of the first tank (Right hand side), I switch to the left and it only shows half full

I've replaced both gas caps so I know they're not leaking, and they're locked.

I know that the guage isn't just wacky since both times I've had to add another 12 gallons to the left tank to bring it full- so now I've lost close to $60 in gas somehow!!!!!

I know it's not leaking cause there's no drips or gas smell, or wet areas anywhere in the area.

My question is, if I have the tank selector on the right side, what is stopping the gas from being drawn from the left side?

If I'm severely off camber off road, will gas from the left tank flow to the right and vice versa?

Will there be some sort of vacuum trhough the right tank that draws a bit from the left as I'm driving? In tank pump? How does it work on a '78 K20 with dual tanks?

I'm just trying to figure out where 25 gallons of gas went!!!!

 

[thatK30guy]

Try a new selector switch.

I had one go bad on an '81 K10 once. One side tank would work and read fine. The other side didn't. Got a new switch and presto! Gauge worked like it should.

 

[monster man]

I know the switch may be flaky, but could it cause it to draw from both tanks at once? I've filled the left and right sides twice now, but each time I run out of gas in the right tank, the left is ten gallons down as well (I've had to add ten gallons each time), so I know that it's reading correctly when it reads empty.

Could the switch be causing the pumps or valves or whatever to malfunction?

 

[big83chevy4x4]

it could be the switch on the frame, switching from one tank to the other. it may be bad and not fully switching, or not sealing fully and pulling from the other tank.

i know with my dual tanks, i had one leaking and replaced it with a 20 gal (originally a 16 gal). what i didn't know was the 20 gal, the sender hole is 4" back on the 20 compared to the 16 and it kinked the feed line, it would pull it out of one and send it to the other. i had 20 gal that i could never use.

 

[Russell]

I'd be watching for the guy with the siphon hose!

 

[davesanrn]

my first guess would be the switch valve is letting the fuel levels equalize, in other words it is leaking from tank to tank.

 

[monster man]

I believe that's the most likely explanation- I only filled the left side tank last night, so the right was totally empty. When I left for work the left tank read at 3/4 full, and the right was now up to 1/2!

At least I know the gas isn't disappearing, thanks guys