Overfill Fuel Seepage

[daniel123]

I replaced the sending unit (and fuel lines) on my '99 200 Osprey last spring. We had to use one over-sized bolt on the sending unit cap to get it to tighten atop the fuel tank as the threads on the tank were stripped, but it appeared that with the gasket it was tight. I had the boat out a couple of times locally since replacing the lines and there were no issues. Then last week I (literally; gas was starting to bubble out of the vent when I stopped) topped off the tank at a gas station, towed it 100 miles, and launched it atop a rather rough Lake Erie. I started smelling fuel on the bumpy ride over to South Bass, and when we arrived I pulled the inspection plate over the fuel sender and saw a shallow pool of fuel had formed around the slight indentation that surrounds the fuel center plate. There also was a sheen of fuel atop the small amount of water in the bilge. I dried off the sender area with a towel and removed all four deck plates to air out the bilge for a few hours while the boat was in the slip. I checked several times over the weekend of use to see if the fuel seepage reoccurred, which it did not, nor did I smell any more fuel then or since.

What I believe happened is that I overfilled the tank and the mid-summer day's heat combined with the bumpy tow and ride combined to build enough pressure to force some fuel to seep out from around the sender unit cap, and once some fuel was burned off, it allowed room for expansion. My plan is to be careful not to overfill the fuel tank in the future and see if that keeps the problem from occurring again.

Another thought is to coat the edges and bolt-heads of the fuel sender cap with Seal-It or a fuel-resistant epoxy to seal it tight to the fuel tank. Would that work to solve the problem?



Dan

[hydraulicane]

definitely gotta fix that problem. any pics? there are some fuel resistant epoxy's out there.
when you say fuel was bubbling out the vent, do you mean the sender?
would like to see some pics if possible.

if no pics just use some fuel resistant epoxy where the problem exists.
or pull the tank out send it to get fixed.

[daniel123]

Thanks for the reply, Hydra. Pulling the tank is a huge endeavor in that boat, and I didn't take photos of the gas around the sender when it was pooled there, but it's the common set-up. I can try to take a photo and put it on my photo section, but it will be at least week before I can do that. And yes, I believe the gas leaked out (how much, I don't know, but would guess a few ounces at most) around the cap/top piece on the sender, which bolts to the tank and we just replaced, noting at least one hole's threads were compromised. I realize that using epoxy to cement the sender in place would make the next sender replacement very difficult, but if it remedies the problem and keeps me from having to cut the floor out of my boat, it might be worth it. Is there a brand you recommend?

[daniel123]

And I meant that fuel was 'bubbling' or spraying out the air vent off the fuel fill hose when I topped off the tank, not bubbling from the sender. The only reason I suspect the fuel I smelled was coming from around the sender cap (instead of a loose hose clamp or other connection from the recent fuel-line replacement job)  was that when I popped the inspection plate over it, there was fuel or fuel/water mix pooled around the slight indent around the sender attachment plate.

[Georgie]

Daniel,

Not sure if you mentioned elsehwere or not, but what material tank?  alum or poly?  Regardless, the sending unit should seal properly to the top of the tank simply with the rubber gasket provided with your new sender.  You can buy replacements if yours is damaged, deteriorated or otherwise isn't sealing well.  No additional epoxy or sealants should be necessary b/c the elasticity of the rubber molds to the texture and contours of the tank (unless you have some sort of major slag on the aluminum or serious warping of the poly).  The fuel seeped out from under the sending unit for a combination of reasons:  1) b/c it's obviously not sealed 100%, 2) you likely topped the tank off at the fuel station so there was no airspace separating the fuel from the sending unit (gravity could no longer force any splashing fuel to drain downhill back into the tank), and 3) underway the fuel all moves to the back of the tank and is mildly pressurized by acceleration due to simple newtonian laws of motion as well as increased hydraulic head as the tank tilt's toward vertical with the attitude of the hull.  

the mid-summer day's heat combined with the bumpy tow and ride combined to build enough pressure to force some fuel to seep out from around the sender unit cap

The airvent prevents the tank from pressurizing at all due to heat or other environmental factors. Only motion or head can affect ambient atmospheric pressure in a vented system (See also Bernoulli's principle).

See if you can positively identify EXACTLY where the fuel is coming from, and then you'll be able to better formulate a plan of action.  This may sound basic, but did you adequately tighten the sender bolts to fully compress the gasket?

[Georgie]

Daniel,

Just want to add that I in NO way meant to sound condescending or rude.  Just re-read my post and to me it sounds terrible, so please pardon my haste in verbiage as I was trying to squeeze in the response at work.

[daniel123]

Ryan,

I've been out and off the grid for a couple weeks and just got this, and your advice is very welcome and not taken with anything but gratitude! I did literally top off that tank and probably put more gas in than was prudent. And when installing the new sender I torqued those screws down as best I could, considering one was stripped, and will check them again. Meanwhile, I'll watch the bilge and tank and sniff for fumes and see what transpires during the balance of the season.
Thanks you for taking the time and thought to give me such good advice.

Dan

[Georgie]

If one of your sender screw holes is stripped then you really need to over-drill and re-tap the hole for a larger diameter screw.  Likewise, you absolutely need a new screw if it's the fastener that's actually stripped.  Not being able to torque that one screw is probably the entire problem.  You won't be able to get a full 360 degree seal on the gasket and it will continue to allow fuel to seep out...even worse, it can allow water/moisture INTO the tank!  

Check out CTSalt's thread...
http://www.classicaquasport.com/phpbb3/viewtopic.php?f=1&t=11147

Is your tank poly or aluminum?

[daniel123]

My tank is poly. Unless it's submerged, how would moisture get in?

Dan

[daniel123]

I just read the link and there's good info in there. My tank on my 1999 Osprey 200, which I believe is poly and original, is brown/reddish in color. Does that sound right?

Matt never got an answer to his final question about expansion and seeping via the sender plate and how common that is. I'm curious too.

As for a better seal/seating my sender plate, would a thicker gasket help offset the stripped threads/screws issue? How about bedding the sender plate with 5200 and the screws? I don't look forward to drilling/tapping that area if it can be avoided.  

Dan

[Georgie]

Daniel,

Few things:

All the tanks I've seen are a tan/brownish color.

Matt never got an answer to his final question about expansion and seeping via the sender plate and how common that is. I'm curious too.

If the poly tank is depressed at all in the area surrounding the sending unit such that water can pool in that area (as was CTSalt's), then seepage is common.  I just helped my neighbor remove over 50 gallons of WATER from his 65 gallon poly tank    that all seeped in through a failed seal around the sending unit which was not even obvious without removal of the unit.  Therefore, the sending unit really MUST be firmly and completely sealed to the tank or water can definitely make its way through the gasket simply via gravity and hydraulic conductivity b/c the tank is not pressurized.

Can you tell me if your tank has the internal molded plastic teardrops with factory press/heat fit threaded metal inserts for your sending unit screws?  Did you re-tap the threads before putting in the oversized screw last time?  In my opinion, the ONLY way to properly save the tank will be to carefully drill, retap, and install oversized screws for each one of the factory fittings that's corroded or currently compromised to the point where you can't properly torque it down.  You should need no more than one new gasket underneath the sender properly torqued to make a tight seal on the top of your tank so that fuel can't seep out even if you pressurize it by overfilling your tank again.  A thicker gasket is a bad idea because it will reduce the number of threads for each screw holding the sender and therefore reduce the ability to compress the gasket.   Use a brand new tap so it cuts as cleanly as possible, try to use the same thread screw with the oversized diameter so the matching tap chases the old threads instead of cutting completely new ones, and make sure you finish with a bottom tap (or adequately ground down plug tap) to remove taper so that the the newly threaded hole will not bind the oversized screw.  Once complete, you should be able to lock down each screw very tight and thereby compress the rubber gasket adequately for a complete seal.  I don't know the an actual torque setting to recommend, but you should definitely make sure each is torqued the same to compress the gasket equally around the entire circumference.

If this project is done correctly, 5200 should not be necessary (nor do I recommend using any type of sealant in combination with the poly and the rubber).  You'd just be asking for an inopportune failure in my opinion.

Good luck and keep us posted.

[daniel123]

Thanks for the very detailed advice, Ryan. I'm not sure about the threaded holes; I'll look at some photos of when the sender was off and see if I can tell. What's the problem with combining 5200 and gaskets?

[daniel123]

Check out the old sender photos I just posted to my gallery, Ryan, and see if they tell you anything about the type of sender fitting my tank may offer. And again: thanks for your advice.