Air in the (diesel) fuel line

[Geoff Safron]

I've been chasing down pesky air leaks in my fuel system (CD '30, 13-hp Volvo Penta diesel); I finally exorcised my biggest demon by re-seating the aluminum tank fitting with Teflon thread compound...but, it seems I still suck air when the fuel tank is half-full or less and I'm dealing with seas rougher than 2-3'. I've literally re-mounted every fitting in the system, so I can only guess that the fuel-tank is getting shaken like a martini-mixer and the suction-tube is sucking air...could this be true? Is there any solution beyond keeping my tank 3/4 full or more (not always possible, of course!)? Is there some sort of ball-valve I could attatch to the bottom of the suction tube? I also wonder about the expansion/contraction differential of an aluminum fitting in a stainless tank, not to mention galvanic problems...any insight here? Help! This is driving me buggy! Geoff



Brainstorm@Unidial.com

[Dana Arenius]

Geoff,

I know this sounds funny but....
Is the suction tube all there or has some of it disappeared? You indicated you may have removed it in order to reseal the fitting.

The shaking of the fuel does not make a lot of sense or many boats would already be in trouble.

Dana



darenius@aol.com

[Tom Coons]

I've been chasing down pesky air leaks in my fuel system (CD '30, 13-hp Volvo Penta diesel); I finally exorcised my biggest demon by re-seating the aluminum tank fitting with Teflon thread compound...but, it seems I still suck air when the fuel tank is half-full or less and I'm dealing with seas rougher than 2-3'. I've literally re-mounted every fitting in the system, so I can only guess that the fuel-tank is getting shaken like a martini-mixer and the suction-tube is sucking air...could this be true? Is there any solution beyond keeping my tank 3/4 full or more (not always possible, of course!)? Is there some sort of ball-valve I could attatch to the bottom of the suction tube? I also wonder about the expansion/contraction differential of an aluminum fitting in a stainless tank, not to mention galvanic problems...any insight here? Help! This is driving me buggy! Geoff

Geoff, I sounds like you've tried all the likely possibilities so here's a couple of long shots. There IS a galvanic problem between aluminum and ss or steel. On a friend's boat the pickup tube that runs to the bottom of the tank to pick up fuel had corroded away due to galvanic action so that it became airborne before the fuel ran out. He replaced it with a plastic pipe and resolved the problem. Here's a second possibility: If you've used so-called fuel conditioner in a very dirty tank. The way some conditioners work is so form a sort of gel around impurities. This glob is now too big to pass through the filters and is held back by them. If you started with dirty fuel it may just be packing up the filters and causing a vacuum in the line which reads as air. Since it runs OK when the tank is full this probably isn't it, but we're grasping at straws here. Good luck Tom



TacCambria@thegrid.net

[Paul D.]

I've been chasing down pesky air leaks in my fuel system (CD '30, 13-hp Volvo Penta diesel); I finally exorcised my biggest demon by re-seating the aluminum tank fitting with Teflon thread compound...but, it seems I still suck air when the fuel tank is half-full or less and I'm dealing with seas rougher than 2-3'. I've literally re-mounted every fitting in the system, so I can only guess that the fuel-tank is getting shaken like a martini-mixer and the suction-tube is sucking air...could this be true? Is there any solution beyond keeping my tank 3/4 full or more (not always possible, of course!)? Is there some sort of ball-valve I could attatch to the bottom of the suction tube? I also wonder about the expansion/contraction differential of an aluminum fitting in a stainless tank, not to mention galvanic problems...any insight here? Help! This is driving me buggy! Geoff

Geoff,

We had a similar problem on a friend's Irwin 38 with a Westerbeke motor. It worked fine but after sailing it would suck air and I would have to bleed the lines. We finally found that the suction tube strainer in the tank bottom was clogged with a vile sludge. It was not getting any fuel. He had long been using soy diesel. After a thorough cleaning and complete tank evac it now seems fine. Hope this helps and good luck,
Paul



nyem0001@tc.umn.edu