Finding Fuel leak sources

edclee · #1 01-23-2022, 10:39 AM

I am in the process if finding and fixing seeps in my port side tank. I see two leaking rivet heads on the outboard portion of the tank in the area of the outermost bay. Weird that it does not leak from the seam of the rear baffle but at the rivet heads of two rivets that don't even go into the tank, just the outer flange. At least I know where they are leaking because I can see the fuel. Problem is that I also have some kind of seep somewhere on the innermost (next to the fuselage) part of the tank. When on the plane I can see evidence of fuel seeped from somewhere there showing up on the bottom skin. I have had this tank on and off the 9A now four times hunting these leaks.

The seeps are so minor that it takes days for some evidence shows up on the bottom skin but the seep so little that none ever reaches the floor of the hangar. I have the tank out now...again trying to detect where the innermost seeps might be from. The tank is capped off, filled with 18 gallons and sitting on a work table anchored in such a way that it is oriented exactly as it is on the wing. The filler cap is on but not sealed so no pressure can build in the tank. Three days now and no evidence of seeps but it has been cold, near or at freezing. I am wondering if it only leaks where the temp is higher?

I cant fix what I cant find...anyone else been through this?
Ed

00Dan · #2 01-23-2022, 10:43 AM

Since you have the tank off already, I’d drain it and do a soapy water test with the tank lightly pressurized.

wcalvert · #3 01-23-2022, 10:56 AM

Since you're not seeing the tank leak off the plane, any chance it was some of the plumbing joints leaking and dripping onto the skin, then showing stains elsewhere?

... you probably didn't want to hear that question.

John Tierney · #4 01-23-2022, 02:32 PM

My fuel smell in the cockpit problem was from the rubber gasket under the fuel level sender unit. The fuel leak was initially not visible.
My early RV-7 plans/instructions showed the gasket, but later Van's plan revisions eliminated it. No amount of tightening the screws would tighten up the rubber gasket, as it was cracking and disintegrating.

edclee · #5 01-23-2022, 03:18 PM

Quote:

Originally Posted by John Tierney

My fuel smell in the cockpit problem was from the rubber gasket under the fuel level sender unit. The fuel leak was initially not visible.
My early RV-7 plans/instructions showed the gasket, but later Van's plan revisions eliminated it. No amount of tightening the screws would tighten up the rubber gasket, as it was cracking and disintegrating.

I am monitoring the rubber gasket carefully. It has now been off the wing and full of fuel and tilted to duplicate the dihedral angle and no sign yet of any seepage from that gasket, but it still could happen there. I have sprayed the whole area with spray foot powder that will show any dampness, even fumes immediately. No evidence yet. The other poster may be correct however, it COULD be a seep from the fitting to hose joint, since with the tank off, there is no gas there.

As for the poster suggesting soap bubbles, when I was chasing the oozing rivets on the outboard side, pressurizing the tank with a balloon would not produce leakage of air sufficient to form bubbles at those rivets even though I knew for certain they were oozing since I could see the gas collect over the period of hours and discolor the foot powder. It took hours however.
Ed

bruceh · #6 01-23-2022, 04:50 PM

Get the tank repair kits from Van's and open up the tanks at the back baffle with a 5" hole saw. Then go in the tank and clean up any obviously softened proseal, then reseal. It is time consuming, but you will be able to get the tank leak free. The worst part of this is getting the tank off the wing, and you've already done that. I've done my share of leak fixing. Read my blog link in my signature block below.

rocketbob · #7 01-23-2022, 05:19 PM

For leaks in tanks this method works well as I have used it a number of times on certified aircraft. Take a harbor freight vacuum pump and plumb it to a fuel drain. Seal off any openings like the fuel cap with tape and plug the vent. Blip the switch on the vacuum pump to draw a vacuum until there's a slight amount of bowing between ribs. Be careful, very easy to overdo. Then take a mechanic's stethoscope and use it to listen for leaks. Once you find the leaks use proseal to stop the leak and to draw in the sealant. Once the tank holds a vacuum you have stopped the leaks.

Kyle Boatright · #8 01-23-2022, 05:34 PM

Quote:

Originally Posted by rocketbob

For leaks in tanks this method works well as I have used it a number of times on certified aircraft. Take a harbor freight vacuum pump and plumb it to a fuel drain.

One of the manual pumps or one of the electric pumps for refrigerant? Even better, a link would be awesome.

00Dan · #9 01-23-2022, 06:15 PM

Quote:

Originally Posted by rocketbob

For leaks in tanks this method works well as I have used it a number of times on certified aircraft. Take a harbor freight vacuum pump and plumb it to a fuel drain. Seal off any openings like the fuel cap with tape and plug the vent. Blip the switch on the vacuum pump to draw a vacuum until there's a slight amount of bowing between ribs. Be careful, very easy to overdo. Then take a mechanic's stethoscope and use it to listen for leaks. Once you find the leaks use proseal to stop the leak and to draw in the sealant. Once the tank holds a vacuum you have stopped the leaks.

Do you thin the pro seal any to make it draw in easier? Or are you using that other less viscous variant meant for gaskets?

RVbySDI · #10 01-23-2022, 06:26 PM

Quote:

Originally Posted by edclee

. . .I cant fix what I cant find...anyone else been through this?
Ed

Many of us have been through this issue of finding fuel leaks. Me included. I can attest to the fact that your statement above is correct. You have to find the leak first. Having a tank sitting on a table full of fuel is a slow, if not impossible, way to find a leak. As others have said already, drain the tank, seal it off, pressurize it and spray the soapy water. You WILL find a leak this way! Oh, and by the way, that balloon has nothing to do with finding the leak, or even knowing that your tank is not leaking. Its sole purpose is to provide a relief valve if too much pressure is pumped into the tank!

Trust those who have been there before you. It does work.

One other thing, once you do find the leak, you will only successfully fix the leak from inside the tank not by slathering proseal on the outside of the tank. Someone already gave you the good advice of ordering the Vans tank repair kit. They do indeed work.

Happy hunting!