Second fuel tank leaks some of the time

I have dual factory tanks. Both tanks work, in that the gas gauge reflects properly depending on what tank I'm on, and the truck runs fine from either tank.

The problem I'm having is that the right tank leaks fuel some of the time. It appears to be coming from an overflow hose on the top. When it leaks, it's a steady heavy stream. I figured I got the tank too full and needed to consume some of the fuel, but I got it down below a half a tank and it still does it. If it's leaking and I switch to the left tank, the leak stops instantly.

Thanks

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MisterB said:

I have dual factory tanks. Both tanks work, in that the gas gauge reflects properly depending on what tank I'm on, and the truck runs fine from either tank.

The problem I'm having is that the right tank leaks fuel some of the time. It appears to be coming from an overflow hose on the top. When it leaks, it's a steady heavy stream. I figured I got the tank too full and needed to consume some of the fuel, but I got it down below a half a tank and it still does it. If it's leaking and I switch to the left tank, the leak stops instantly.

Thanks

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Does your tank have a return (3 lines on top)?

MisterB said:

I have dual factory tanks. Both tanks work, in that the gas gauge reflects properly depending on what tank I'm on, and the truck runs fine from either tank.

The problem I'm having is that the right tank leaks fuel some of the time. It appears to be coming from an overflow hose on the top. When it leaks, it's a steady heavy stream. I figured I got the tank too full and needed to consume some of the fuel, but I got it down below a half a tank and it still does it. If it's leaking and I switch to the left tank, the leak stops instantly.

Thanks

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I wouldn't know what the deal is, I'd have to take a guess on some Kind of negative /positive pressure?

Maybe I'm just a blubbering idiot here

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Frankenchevy said:

Does your tank have a return (3 lines on top)?

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Not sure. I'll look and report back

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MisterB said:

Not sure. I'll look and report back

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My theory based on your initial post is that you have a split in that tanks return line. A return style mech pump will pump unused fuel back to the tank through the sender. Since the leak stops instantly when you switch tanks, it seems to make sense.

An easy way to tell if you can’t see 3 lines by looking between the cab and bed, is to look at the pump on the engine block. Does it have three lines?

3 Lines. Disregard the rubber fuel line on the inside of the passenger frame rail.

As you can see in the picture in the last post, there are three rubber lines connected to each tank (if you have a return lilne), and then if you look up at the tank solenoid under the truck there will be more rubber hoses to connect the solenoid to the two tanks and to the metal line running to the engine compartment - lots of rubber hoses! Then up in the engine compartment there will be two rubber hoses connected to the fuel pump (along with one metal line), and most folks have two more rubber hoses where they spliced into the metal carburetor fuel line to add an external filter. There are lots of places for small leaks in old hoses, and every time I fixed one it seemed like another leak started in a different hose.

I bit the bullet and bought new SAE J30R9 EFI grade hose and clamps for my fuel hoses, and then replaced them one by one. The J30R9 (high pressure) or J30R7 (low pressure) rubber hose is supposed to hold up better to the new fuel with Ethanol. It was too expensive to buy at the parts store by the foot, so I found a place on Amazon that sold it in 10 foot sections. I needed to buy three sizes (1/4", 5/16" and 3/8"), so it got fairly expensive. However, I hope it ends my fuel leaks.

Bruce

I had a similar issue after doing a tank replacement. When I filled the tank it would leak at the station and when I accelerated. It ended up being a loose vent hose.

Kasey 1977 K10 said:

I had a similar issue after doing a tank replacement. When I filled the tank it would leak at the station and when I accelerated. It ended up being a loose vent hose.

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Is the vent hose the little 3" or so hose at the top with the angled cut to it?

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MisterB said:

I have dual factory tanks. Both tanks work, in that the gas gauge reflects properly depending on what tank I'm on, and the truck runs fine from either tank.

The problem I'm having is that the right tank leaks fuel some of the time. It appears to be coming from an overflow hose on the top. When it leaks, it's a steady heavy stream. I figured I got the tank too full and needed to consume some of the fuel, but I got it down below a half a tank and it still does it. If it's leaking and I switch to the left tank, the leak stops instantly.

Thanks

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Click to expand...

I will have the same issue. Well similar, mine seems to only happen if full, seems I think I notice it in the summer and mine is only a drip every 5-10 seconds. I figured it was from fuel pressure from expanding and full tank in heat. I have not looked into it very much as it is so random and not much when it does it .