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Author Topic:   Water in fuel tank
leapinlunker posted 09-18-2008 08:19 AM ET (US)   Profile for leapinlunker   Send Email to leapinlunker  
Some of you may remember we had to have our fuel tank replaced in the 24 Outrage. Since that time we have had a continuous problem with water getting into the tank. I have had the tank drained and all liquid removed, yet the problem persists.

This summer I have run approximately 470 gallons of fuel thru her and have had to change and or drain both the on-motor fuel filters, as well as, the aux filters. What perplex's me is how water is getting into the fuel. I, at first, thought that a fitting was loose or that the fuel vent had been reinstalled at an improper angle. Not the case. I have bought fuel from several different places, including Canada (ouch) and still have the problem. I just can't believe that condensation can create the volume of water that is causing my sensors to go off.

When I drain the filters, I put the liquid into a glass jar and let it settle. Sure enough, there is water on the bottom.

Any thoughts? I sure hate to tear out that floor again.

contender posted 09-18-2008 09:38 AM ET (US)     Profile for contender  Send Email to contender     
Hate to say it but you may have a leak, Do you smell, see any fuel in the bilge? Need to check your fuel fill line could have a small tear. Also your vent line near the tank. Probably one way to check before tearing the floor out again, drain the tank (Get all the fuel and water out have to start new and empty), now fill it, use it, and when you return (that day) stop at the gas station and fill the tank again. If the tank is full should not make any condensation so any water you picked up would be from a leak in the tank (or water in the new fuel). Another way if you can make your connections all air tight, (vent, gas fill) put air pressure in the tank and see if it holds. Was the tank new? The tank should have been pressure tested by the builder for 24 hours before selling it/setting in the boat, Sorry for your problem...good luck
jimh posted 09-18-2008 09:15 PM ET (US)     Profile for jimh  Send Email to jimh     
Testing the integrity of the fuel tank with air pressure is a valid test, but be sure to carefully limit the amount of pressure. Typically only a a very small pressure is used. If you calculate the surface area of the tank in square inches, you can see how even a pressure as low as 2-PSI can apply a great deal of force on the tank.
seabob4 posted 09-18-2008 09:38 PM ET (US)     Profile for seabob4  Send Email to seabob4     
To test your tank, fill it with air to 3 PSI, CG and NMMA/ABYC requirements, close the shutoff valve, observe gauge for 14 minutes. If it doesn't maintain 3 PSI, check all hose connections, then repeat test. If gauge drops, you have a leak.
towboater posted 09-19-2008 02:23 AM ET (US)     Profile for towboater  Send Email to towboater     
I have a tough time thinking your new tank is leaking also, but, air testing is very good advice.

I assume you discover water in your filters because your engine runs like shit and first thing you do is check the filters.

Have you been mixing in additives?
(I will be out of town this weekend so allow me to ramble).

Today, the water separators are so efficient, additives to remove water can actually plug the filter worse than water itself. A small amount of water in a filter is normal, that is what they do. If you need to let the drained fuel set to reveal water, Im not so sure that is the entire problem. Ethanol gas magnifies the water issue. Consider upgrade your filter so it has a sight glass and drain before you tear up the deck.

Carry a small gas can with fresh gas that has no water in it. Next time your engine starts running bad, usually backfires, try drawing fresh fuel from the gas can and see if your engine doesnt perk up. If it doesnt, you have a problem with the motor. Check the fuel pump pressure & distributor.

Disclaimer. The gas can test might sound risky, but, no more risk than air testing the tank. Either way, be careful. Good luck.

mk

contender posted 09-19-2008 05:30 PM ET (US)     Profile for contender  Send Email to contender     
Air test should be done on an empty tank...
Martino posted 09-19-2008 08:15 PM ET (US)     Profile for Martino  Send Email to Martino     
Fuel filler cap seal in decent shape? On my revenge, the vent line had a big loop in it so that the high point was above the height of the vent. Does yours have that? Wondering if someone removed the piece of tubing which allows this configuration.
leapinlunker posted 09-20-2008 08:55 AM ET (US)     Profile for leapinlunker  Send Email to leapinlunker     
Air test will be done this week. Will advise. Thanks.

Terry

jimh posted 09-21-2008 10:36 AM ET (US)     Profile for jimh  Send Email to jimh     
Assume a fuel tank is a cube with each side 10-inches long. This tank has a volume of 10 x 10 x 10 = 1,000 cubic inches. The tank has six sides, and each side has 10 x 10 = 100 square inches. Thus when empty the tank has a total surface area of 600 square inches.

1 US gallon = 231 cubic inches

If the tank is filled with gasoline it will contain

1000 / 231 = 4.33 gallons of gasoline

1 gallon of gasoline = 6.25-lbs

The gasoline in the tank will weight

4.33 gallons X 6.25-lbs/gallon = 27-lbs

If we assumed for a moment that all 27-lbs of the gasoline bears only on one face of the tank, the bottom, and ignore the side wall pressure, we would have a force acting on the tank of

27-lbs / 100-square-inches = 0.27-pounds/square-inch or 0.27-PSI

Now we fill the tank with air to a pressure of 3-PSI. There is 600-square inches of surface receiving this pressure because it acts on all six sides. The force exerted is therefore

600-square-inches X 3-lbs/square-inch = 1,800-lbs

Now we compare the forces:

From gasoline = 27-lbs
From air pressure = 1,800-lbs (66 times more)

Also the pressures:

From gasoline = 0.27-PSI
From air pressure = 3-PSI (11 times more)

Thus we see that pressure testing the tank by filling it with air to a pressure of 3-PSI is a very substantial increase in the pressure and force on the tank that normally would occur from its liquid contents. A test at 3-PSI ought to be a very good test for the existence of any leak.

seabob4 posted 09-21-2008 01:25 PM ET (US)     Profile for seabob4  Send Email to seabob4     
Another part of an air pressure test. Mix up a soapy solution (any dish detergent will do) and brush it onto the welds around your fill neck, vent neck, pickup and sender welds, and any welds you can reach. Any leak will present itself with bubbles.
contender posted 09-21-2008 08:11 PM ET (US)     Profile for contender  Send Email to contender     
Good one seabob forgot about the soap, put it in a spray bottle easy to apply
seabob4 posted 09-21-2008 08:13 PM ET (US)     Profile for seabob4  Send Email to seabob4     
Contender,
When I was at Stamas, they were too cheap to provide spray bottles!
4whaler posted 09-22-2008 12:06 PM ET (US)     Profile for 4whaler  Send Email to 4whaler     
When I had my 1978 21 Revenge take out I noticed some pitting especially where the air couldn't get to the take surface. So I did the air pressure and soap spray test. Sure enough there was a pin hole at the weld of the vent hose elbow. None at the pitting areas. I use a aluminum weld rod to patch the hole. Tank had been empty for 3 years in my basement with hoses and gas gauge out, so I wasn't worried about welding on it, but I still blew air thru it for about an hour to make sure. I have since reinstalled with a system designed to keep it surrounded by air and have a drain in the bottom of the tank sump to let water into the bilge. I don't know why Whaler chose to put the exit hole at the top of the tank cavity, it makes it a big bath tub even though you have foam surrounding it. I have also put my floor tank cover on so I can lift and air out the cavity when not in use.

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