Pressure testing fuel tank

[GLS062866]

Got a quick question on pressure testing fuel tank. I am either getting some water in my fuel tank slowly or I have not gotten all of it out from the time that I first noticed it. I am going to attempt to pull pick out of tank because I want to make sure that I am removing all of the water that is in the tank and not rely on just what fuel i can pull out with the primer bulb. Once I do that so that I know that I am starting with no water in tank I am going to pressure test the tank since this seams to happen every once in a while even though I am using non-ethanol fuel with fuel treatment each time. The vent line comes through the hull and has a 90 degree female fitting with the vent cover. I am going to just screw a plug in it to block. I know that most of the time one of the air bladders are used to block fuel fill line. My question is if the fuel fill cap is not part of the venting can I just test it with the fill cap on? It has a gasket on it. With testing with only 2 to 3 PSI if it leaks air out under pressure I would think that water could get in also especially with no pressure. Going to use a gauge on a tee with a barb to fuel time right before filter/water separator and air valve on other side. Thoughts on using fuel fill cap vs air bladder?
Thanks.....

[Keithbaja]

The cap is not vented... And every one forgets to check and replace "O" ring that let's water in. Also check the vent line installation.... I've seen several installed incorrect. I've seen tanks not leak when cool and as the day warms up they start to leak... Any signs of gas leaking out ??

[GLS062866]

Not a sign of leaking at all from anywhere.

[Keithbaja]

You might want to check out "phase separation". The ethanol Is killing fuel systems with water. I'm seaing it almost daily. And a lot of water throughout the complete fuel system. Nasty, nasty. I recommend after a complete cleaning of fuel system to use "StarTron" regularly. Sea foam is a GREAT product for other uses

[99yam40]

trying to pump out water with a pickup tube that is not on the very bottom of the tank does not get all the water out of a tank.
you need to open up the tank and tilt it so you can suck as much as possible out for a low corner, but then need to use other things to remove the rest of the water.
there are matts for that

[ausnoelm]

trying to pump out water with a pickup tube that is not on the very bottom of the tank does not get all the water out of a tank.
you need to open up the tank and tilt it so you can suck as much as possible out for a low corner, but then need to use other things to remove the rest of the water.
there are matts for that

This is 100% correct, there can be lots of water left in a tank if you just use the fuel pickup. How water is getting in will require some simple investigation, starting at the filler, the vent, the tank itself and your fuel supply, any one of those things can be suspect, pressure testing is not the answer.

[ausnoelm]

You might want to check out "phase separation". The ethanol Is killing fuel systems with water. I'm seaing it almost daily. And a lot of water throughout the complete fuel system. Nasty, nasty. I recommend after a complete cleaning of fuel system to use "StarTron" regularly. Sea foam is a GREAT product for other uses

How is startron/seafoam going to prevent water? Both products are not for water issues. Almost every engine built for the last decade will run on Ethanol based fuel.

[zenoahphobic]

Funny water dispersants such as WD40 contain alcohol to do that job. Because alcohol absorbs water.

Now, not trying to be controversial, if you had a little water in the bottom of the tank, theoretically adding alcohol (mixed fuel) would absorb that water.
For that then to come out again, lots of evaporation needs to take place. Fine with an open container but a tank will then need to be forcefully ventilated.

So the water that the alcohol precipitated can be redissolved and removed from the tank. Would only recommend small volumes but an air supply like a volume aircompressor into your tank together with a litre of alcohol fuel, over time and well ventilated, might(will) work!

[zenoahphobic]

You need to know the amount of water we are dealing with.

[Keithbaja]

Ausnoelm.. As my post stated.. Seafoam is a great product for other uses.. Not water !! Startron is for stopping phase separation and water contamination... Read up on it my friend... BTW this is what I do for a living..

[TownsendsFJR1300]

I've been using "Gas Shok" in my 1997 Angler.

Prior to 2000, my 1997 150 Evinrude kept clogging the carbs due to varnish (and lack of use).

The local dealer recommended Gas Shok which stopped the carb clogging immediately and since helped keep the fuel fresh

A couple years ago, I pulled 2 year old fuel out (not maybe 15 gallons) but it was just as fresh as new.
I wanted to measure how much fuel was in the tank vs what the Yamaha fuel gauge read (and it's age).

I do have a see thru water separator on the transom.

I've NEVER had water collect either there or the engine filter. .And I'm in a very humid area.

I do use E-free Fuel.


Highly recommended...

[GLS062866]

Thanks for everyone's response. I am going to try and work on it this weekend. I will look at all that has been suggested.
If you don't mind back to my original question about using fill cap vs air bladder to pressure test fittings on tank. If the cap has a good o ring it should seal good enough to test tank? If nothing else it will rule out a small leak in the fill cap seal. Thanks