Fuel Tank Pick Up Tube

[B's 3100]

I recently purchased a 1984 Express Cruiser 3100 with (2) 80 gallon tanks. I was running both engines on the Starboard side tank until it was "empty" and it only took 56 gallons of fuel to full. Port side tanks would not "pump" for prime and only took 25 gallons of fuel. Neither of the fuel gauges work, which I will trouble shoot and fix when I start to fix whatever is going on with fuel lines. My first assumption is that the pickup tubes are shot. the reason for this post is, are the pickup tube welded into these tanks or are they serviceable?

[DaveKamp]

I don't know for absolute certain, but I BELIEVE your '84 3100's tanks are TIG welded aluminum, and I believe the pickup tubes are TIG welded aluminum tubes, but there's other possibilities. The vent tubes were basically always welded in, but that'll be obvious when you see it.

The tanks have sending units that mount into flanges with eeeeehhh... (squinting my left eye while I try to remember) 10? screws holding the sending unit flange into the tank flange. During this vintage, Wellcraft tanks had the sending unit relatively centered in the tank, or slightly forward of center... but don't take that as any sort of a guarantee.

On MANY of these tanks, there's a bung threaded into the tank... like (squinting again) a 3/8" pipe thread. IF you unthread the anti-siphon valve, then back out the 90 degree elbow, you'll probably find another hex fitting that... if you carefully back it out (box end wrench!), it will withdraw a short nipple into which is pressed, or possibly threaded with loctite, a metallic tube that ORIGINALLY extended to the bottom of the tank.

When I look into failures like yours, I USUALLY find that a hole has either corroded into the tube at some point, or moisture has frozen and split the tube open, causing it to suck air once down below a certain level.

USUALLY, you'll find that the sending unit and pickup tube point is accessible for service. In SOME setups, you might have to drain the tank a bit (stick a long hose down the filler, and pump/siphon it out), and once it's light enough, unfasten the retainers (usually screws into flanges or strap), then shift the tank fore, aft, or sideways, or some combination of the three, to get the hardware lined up with a strategically-viable spot to pull up the tube and sender.