Water Intrusion Fuel Tank Chamber 175

[CTsalt12]

Hello CA Community,

It's been awhile since I've had to enlist your help, but I have an issue I just can't seem to figure out.  I have fresh water pooling up on top of my below-deck fuel tank on my 175.  It's a poly tank, non original obviously.  It gets in through the sender and into the tank, bad news all around.  So I've been running on remote tank since I discovered this.  I've been told by my boat guy that I need to address the water pooling up on top of tank first thing, more important than how it gets in through sender.  Supposedly senders are designed to keep fuel in primarily, and not to keep water out.  

So I have 2 hatches above my tank on the deck plate: one stock under the console, and one aftermarket exposed which is at your feet when you're at the helm.  I have tested the exposed one by spraying water full blast on it, point blank range for a while, no water intrusion.  The one under the console is an old rotted hatch for sure, but there is no water getting into my console anyway...It's caulked (although not that well, and a cover goes on top of  it.  After a heavy rain I don't see any water pooled up or moisture under the console.  I have no idea how else water can be getting in.  I just re-caulked the fuel tank hatch this past year and did a very precise job.  

Any ideas here on how to proceed?  Help much appreciated, I am stuck using a remote tank with a useless new 25 gallon below deck...

[wingtime]

I was going to say the pie plate is leaking.  Not all pie plates are created equal and some do leak.  Id check to make sure it has a good O-ring on it.  Pie plates are cheap so replacing it may not be a bad idea.  Be sure to bed the plate and screws well with 5200.  The next place it could be leaking is thru screw holes in the coffin cover.  Those include the screws holding down our console and your seat.  I'd go around with a screw driver and look for loose screws.  In fact if it was me I'd remove each screw and rebed each one with a healthy amount of 5200.  Screws in an older boat tend to loosen up with time.  Then they leak allowing water intrusion that can cause core materials to rot etc.  This is just normal old boat maintenance that gets overlooked by most owners.

[CTsalt12]

I was going to say the pie plate is leaking.  Not all pie plates are created equal and some do leak.  Id check to make sure it has a good O-ring on it.  Pie plates are cheap so replacing it may not be a bad idea.  Be sure to bed the plate and screws well with 5200.  The next place it could be leaking is thru screw holes in the coffin cover.  Those include the screws holding down our console and your seat.  I'd go around with a screw driver and look for loose screws.  In fact if it was me I'd remove each screw and rebed each one with a healthy amount of 5200.  Screws in an older boat tend to loosen up with time.  Then they leak allowing water intrusion that can cause core materials to rot etc.  This is just normal old boat maintenance that gets overlooked by most owners.

All good ideas wingtime, Thanks.  I actually didn't think of screw holes, seems like such a small amount of water that would be getting through, but at this point it's time to check everything.  There are a few console screws that go into my coffin cover.  Couldn't be the seat screws, they are outside coffin.  The coffin cover screws are bedded well, and If I'm correct it's designed in such a way that any water coming through those holes would go into a flange around the coffin and not  into it.

[wingtime]

No if it gets into the coffin flange its getting into the coffin.  There isn't a built in gutter around the coffin. The deck and coffin are all one molded piece.  the coffin cover just sits in a lip.  You can see how the coffin looks on my 1981 200XF that I had:

[CTsalt12]

Actually the 89 does have gutters around the tank coffin top.  Just took a look at a picture I took when I pulled floor up around this time last year.  Look at the top of the picture.

[Capt. Bob]

CT,
How about a pic of the underside of your tank coffin cover? I'm guessing you have a deck plate access over the sender/fuel fill area correct?
Looks like water is standing around the sending unit and is weeping in as you suggested. At this point, depending on the senders age, you can replace with a new one or as suggested, replace the gasket but............

If there is an access plate, it is your water intrusion point.

Classic deck plate leak.

[wingtime]

hard to tell of those are actual gutters in that pic.  Most of the ones I have seen are just a 3/4"-1" offset to allow the cover to sit level with the deck.  I haven't had to cover off my 170 YET.

[CTsalt12]

CT,
How about a pic of the underside of your tank coffin cover? I'm guessing you have a deck plate access over the sender/fuel fill area correct?
Looks like water is standing around the sending unit and is weeping in as you suggested. At this point, depending on the senders age, you can replace with a new one or as suggested, replace the gasket but............

If there is an access plate, it is your water intrusion point.

Classic deck plate leak.

I don't have a pic of the underside of the coffin cover unfortunately.  Haven't pulled it since this time last year and hoping to get away with not having to pull it again.  I have 2 access points, 1 designed for the original fuel tank that is under the console, and one I installed for the new fuel tank P.O. put in, which is pictured.  I put weather stripping in that one because the fuel line pushes it up and creates a gap.  Fuel line is un-attached in this picture.  

Unfortunately, I don't think either of these are the culprit.  That would be an easy solution.  I have tested them both with heavy spray and pouring buckets of water in.  One thing I thought of last night is the battery box tie downs.  There are in total at least 10 screws holding the battery box ties in place on top of the coffin cover in the console.  My  mechanic installed the new ones and not sure if he used sealant, the old ones are ancient and any sealant is probably worn away by now anyway.

I am not putting new fuel into the tank until I stop getting water sitting on top.  Senders can't be trusted to keep water out and I want to get to the root cause of the problem.  

[CTsalt12]

Side note: does anyone have ideas for an elbow piece for the fuel fill line?  That's the plastic tube built into the tank where the hose is disconnected.

Actually, I am thinking of just filling up gas directly through the fuel fill line neck (the plastic piece built into tank).  The tank doesn't have enough room on top, it causes the tank to warp which creates a bad seal in the sender.

Is there any reason I can't fill up right at the tank?  As you can see I have ample room with the hatch I put in.  This is assuming I get something to plug the fill neck with after fill ups.

[CTsalt12]

Bump.  I know someone here has got to know the answer here: I am thinking of just filling up gas directly to the tank through the deck hatch, and putting a plug over the tank fill when not in use.  Is this hazardous?

[Capt. Bob]

Bump.  I know someone here has got to know the answer here: I am thinking of just filling up gas directly to the tank through the deck hatch, and putting a plug over the tank fill when not in use.   Is this hazardous?

FEDERAL LAW

183.564 - Fuel tank fill system

(a) Each fuel fill opening must be located so that a gasoline overflow of up to five gallons per minute for at least five seconds will not enter the boat when the boat is in its static floating position.


One of the key principles of this regulation is to prevent gasoline from getting inside a boat where it can vaporize and create an explosive atmosphere. Overflow at the fuel fill opening is one potential source of fuel that could get inside a boat unless precautions are taken.

The location of the fuel tank fill opening must be chosen with the following considerations in mind:

    (a) Nearby ventilators, on deck or on the side of a boat, could provide access for fuel to flow inside a boat. The distance between the fuel fill opening and ventilators may have to be increased over that normally considered adequate for keeping vapors from entering ventilators.

    (b) The deck configuration and its slope could channel overflow fuel into a boat.

    (c) High coamings or cabin sides can offer protection against overflow from flowing into a boat,

    (d) Deck joints in riveted construction or wooden construction could provide a path for fuel to flow into the boat’s interior unless they are caulked to resist such fuel leakage.

FIGURE 30 - Fuel Fill Locations

The test to determine compliance is as follows:

    (a) Place the boat in its static floating position - see 183.505

    (b) Plug the fuel tank fill line at least a distance of six inches below the fuel tank fill opening.

    (c) Insert a 13/16 outside diameter hose into the fuel tank fill opening.

    (d) Discharge water at a rate of five gallons per minute (53.3 ounces in five seconds).

    (e) Time the overflowing water for five seconds and shut off the flow.

    (f) Investigate to determine if any of the overflowing water got into the boat. None is permitted in order to comply. Overflow entering a self-bailing cockpit is considered entering the boat and is not permitted.

NOTE:
Interpretation of this requirement by the Coast Guard prohibits fuel fill fittings located in the cockpit sole or in seats inside the gunwales.

[kchaudha]

I have a similar tank sag issue with my poly tank on my 175.   Caused water intrusion last year and I figured the issue was fixed with a sender gasket replacement.
However, I now am noticing that the gasket is leaking again in the other direction, letting fuel out when full on a hot day.  I'm replacing the gasket again with a better one (and taking the opportunity to add the wema sender that I have been wanting).  But after reading this thread, I am wondering if water is still going to come in.
I wonder if a cover/tent could be built over the tank so that even if water gets through, it is not pooling on the top of the tank?  Has anyone thought of this or done this?
Then regarding the hatch - does the entire hatch have to be replaced or can you just replace cover or cover gasket?

[CTsalt12]

Chauda,

Good to know someone else has this issue.  Also good to know the new gasket didn't fix the problem.  I guess I will replace with a WEMA as well and do it right.  As for your hatch, hard to say if you need to replace the whole thing or just o ring.  You probably also have a hatch under your console that might need to be replaced as well.  But that might not be the source of water intrusion in the first place, which is the case for me.  I think I have found a solution for the sag though.  This is what you / I need:

http://www.fillernecksupply.com/servlet ... Categories

or something like this. A 1/2 inch fuel fill elbow with adapters that go inside the hose and fill neck, then you clamp inside on both sides.  Should do the trick but make filling up a bit slower.

Oh, and the cover / tent idea seems a bit crazy.  Better to just keep water out once and for all.

[Capt Matt]

Is this a common problem with poly tanks swelling and then the sending units leaking?
Capt Matt

[CTsalt12]

My tank is contracting and not swelling really.  It's not from temperature change either, just from having not enough space above it for fuel line which presses against deck.  And I'm not so sure the contracting is causing the leaking either, although it is logical.