What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Water Test The Fuel Tanks a bad idea???

dustin_96

Member
I've seen in several youtube videos that builders will fill their fuel tanks with water prior to installing the rear baffle. This gives you a chance to fix those random leaks while you can still get your hands in there! I've noticed that Van's doesn't mention this and through a number of searches here I haven't found any reference to it.

Is this a bad idea for some reason? I suppose my chief concern is making sure the tank is adequately supported so the cradles don't break or damage the skin.

If this has already been discussed, I apologize. My searches just haven't come up with anything.

Thanks!

BTW I'm building a 14A.
 
Lots of discussion and you won't find a consensus. I too leak tested my tanks before installing the back plate; again afterward obviously. One thing that should be indisputable, water is an awful for leak testing fuel tanks. The surface tension (main driving property) is too high.

Fuel is better but has risks. Manageable IMO.
Car gas can take a very long time to reveal any leaks. Avgas is better because of the blue dye -> blue stain. Fuel with UV dye is the quickest and will provide the most certainty IMO.

If you want to use water, add some dye (food coloring) and a lot of surfactant (dish soap will do) but keep in mind, while safe the results will not be with 100% confidence.
 
Thank you! Should you install the fuel senders before conducting the test or fabricate a cover plate for the hole?
 
Reading a thread on sealing tanks the other day I was thinking about this exact question.
and I was thinking it might be better to test it with some fluid with a lower viscosity and lower surface tension than gasoline. I'm not sure what that fluid would be though...and especially one that would be compatible with the materials in question.... alcohol, acetone, some other solvent perhaps? put a little dye in it....add a little pressure...and if that doesn't seep then you're probably pretty good.
 
I used water to test the obvious leaks before closing the baffle and found some. That was easy to do. I could surely have found the same leaks after the baffle was closed but it would be a lot more difficult to fix.
 
My personal opinion would be to test with the senders installed. A universal truth for most any test, you want the highest fidelity possible; configuration, operating conditions, whatever.

I honestly don't imagine a measurable benefit testing with another fluid. You're introducing variables that may not matter.
 
I did this exact thing on my RV6 tanks before installing the rear baffle. I made up a cradle and set them up level with the fuel senders installed and filled them to the baffle level with Jet A1. That stuff will show you a leak for sure and is somewhat safer to use than Avgas and easy to clean out. Good luck
 
How about this?

Take your fuel tanks before installing the rear baffle and dunk them upside down into a pool of water, about a foot down should do it.
Air bubble would appear immediately on any leaky rivets or joints.
I did not test any of my 4 tanks before sealing the rear baffle and haven't had any leaks on any of them.
I do agree, finding a leak before closing up would be preferable over discovering a drip after the tanks are all closed up.
 
Lots of discussion and you won't find a consensus. I too leak tested my tanks before installing the back plate; again afterward obviously. One thing that should be indisputable, water is an awful for leak testing fuel tanks. The surface tension (main driving property) is too high.

Fuel is better but has risks. Manageable IMO.
Car gas can take a very long time to reveal any leaks. Avgas is better because of the blue dye -> blue stain. Fuel with UV dye is the quickest and will provide the most certainty IMO.

If you want to use water, add some dye (food coloring) and a lot of surfactant (dish soap will do) but keep in mind, while safe the results will not be with 100% confidence.

So you could use some soap to break the surface tension. Would that cause any issues with sealant bonding when you try to patch it?
 
Water calibrate

Just so y’all know, i plan to use water to calibrate my fuel level sensors. I can do this in my hangar before i move to some distant airport for first flight. The errors should be really small, like 0.2%.

But adding soap may not be a bad idea to clean the crud out, but then how do you rinse afterwards?
 
So you could use some soap to break the surface tension. Would that cause any issues with sealant bonding when you try to patch it?

Of course. Like so much of these related crafts, surface prep is everything. Would not expect it to be much of a problem for the first check. The backplate is off so the bulk cleaning could be with a garden hose. The second phase wouldn't need much of a fill but I'd still expect a LOT of sloshing for the initial clean. Wasn't advocating for water, just saying that virgin water isn't a great choice. There's no perfect way or there'd be no discussion.

I used ethanol free Mogas/AC Delco UV dye with the tanks in three padded build cradles (stationed at the ribs, of course) and a stack of ripped wood (from 2x8s?? don't remember) for the second test. Two tanks tested then fuel run through my 98' Pathfinder. There's a certain freedom granted in life when your Home Depot car ages.

To the OP, get lots of opinions and keep doing your due diligence. As mentioned, there's no "best" way. Here's hoping there's no leaks in your future.
 
I would not do that

Just so y’all know, i plan to use water to calibrate my fuel level sensors. I can do this in my hangar before i move to some distant airport for first flight. The errors should be really small, like 0.2%.

We are getting away from the testing questions but I would really stay away from water once the tanks are installed.
Calibrating your fuel level is not complicated at all and a visual check on a full tank ( or half tank) is plenty good for your first flight.
 
I appreciate everyone's input. I plan to use water and see how it goes. I know it won't be an absolute test but given that I'm doing it in my attached garage I don't really want to attempt it with any flammable materials. Once the tank is sealed I'll use the pressure test as per Van's instructions and see how it goes.

Thanks again for everyone pitching in!
 
My take

Just my take, but I would not put water in the tanks unless the rear baffle is in place. I don't think the aluminum between the ribs is strong enough by itself to resist bowing. I never tried it so don't know for sure. JMHO
 
Back
Top