Fuel tank leak... but where from?

Erin · 18 June 2006, 21:39

If it's not one thing it's another. First my engine was playing up, and just wouldn't idle properly when cold, then yesterday I find fuel in the bilge.

The bilges were lovely and dry until I refuelled last weekend and brimmed the tank, and all seemed to be well on my first 10 mile trip. But yesterday I went down and found fuel in the bilge sump. Now there's a couple of possible causes, but I'd like some advice as to how to proceed.

I've had a good look around the stainless plate on the top of the fibreglass tank where the filler pipe, gauge sender and fuel feed are all terminated, but I can't see any real signs of fuel other than a thin film. What I can't tell is if it is sloshing around when I'm underway and peeing out the top. Having said that, I'd have thought it was quite a big leak given the amount I found in the bilge. If there's a crack in the tank, how the hell am I going to find it and for that matter repair it seeing as the only visible bit of the tank is the cut out in the floor of the console where the pipes connect?

Any thoughts?

Piccy below of bilge before leak. Float switch has now jammed due to petrol affecting the plastic.

antiqueboy · 18 June 2006, 22:13

thanks for advice for my fuel query, fuel tanks by there nature are pretty bullet proof so i would hope the problem was else where, if you found that it was then i would bite the bullet and replace it rather than fix it
regards
nick

codprawn · 18 June 2006, 23:11

Maybe a breather pipe is loose? Not at the tank but where the breather exits.

fast fred · 18 June 2006, 23:13

"fuel tanks by there nature are pretty bullet proof" you would think that, and for the most part thay are, thare are Losers who put in the saddest tanks,
and close the deak so you can't see how sad it is, seen that kind of crapmanship. hopefully it's just a rubed line.
best way to check the tank is to plug the feed, vent, and put air pressure in through the filler, plug it as close to the tank as you can so to eliminate the lines from the test,
3psi is the norm over hear,should hold 4psi, custom to put a psi gauge on the vent.
FF

Erin · 19 June 2006, 09:06

Quote:

Originally Posted by fast fred

thare are Losers who put in the saddest tanks,
and close the deak so you can't see how sad it is, seen that kind of crapmanship. FF

Hmmmm, I begin to wonder after the problems I had with the hull!

fast fred · 19 June 2006, 12:05

well I have no idea what rib your running, so it may not be the case,
another thing is some put the fill and the vent on the side of the tank, so thay can bring the top of the tank to the under side of the deak, it don't work, the fundamentals of a gas tank are simple, vent and fill are on TOP,
to the front of the tank, pickup goes on the bottom rear. as simple as that is
it not funny how many put them on the side, burpin gas out the vent, burpin out the fill, banging sounds when you fill cuzz the air is traped an can't vent.
hopein it's just a hose for ya

I've removed tanks that should have never even been filled with water, and should have never been called a gas tank.
FF

Erin · 19 June 2006, 19:36

Thanks Fred, but all my connections are on the top as per the photo below. I've used a mirror to look at the gap between top of tank and the underside of the deck, and there's signs of fuel there, but no actual 'puddles' unless it has all now evaporated. I think I'll just have to wait until I top it up again and then look down the gap to see if there's any fresh petrol lake on top!

fast fred · 23 June 2006, 13:22

i'd reseal them two gaskets, the send and the big plate, if you got gas leakin in the bilge with all the lines and hard ware on top, unless it's them gaskets,
it's a good posability you have blown out an upper seam on the tank, seen this before, only seen when the tank is or all most full. thats an easy one to test.

Jono · 23 June 2006, 13:35

There have certainly been issues with "glass" tanks not laminated up with the correct resin.... after time they become porous and eventually fail. Drain and purge your tank then lift the inspection plate and check the state of the laminate.

codprawn · 23 June 2006, 14:57

Quote:

Originally Posted by Jono

There have certainly been issues with "glass" tanks not laminated up with the correct resin.... after time they become porous and eventually fail. Drain and purge your tank then lift the inspection plate and check the state of the laminate.

A worry of mine as well - but surely it would take a bit longer than this to develop?

IF the correct resin is used then they should last for ever - petrol stations tanks are often fibreglass these days.

codprawn · 23 June 2006, 15:10

Just spoken to the great people at Glasplies - they say a special resin should ideally be used BUT there are plenty of people who have used just normal resin for car and motorbike tanks and they have lasted years with no probs at all.

One advantage of fibreglass is they are more flexible so they are less prone to cracking than stainless or ali.

Erin · 23 June 2006, 15:15

So how do you actually make a sealed tank then. How do you remove the mould or plug?

Would I be foolish unscrewing the top plate and re-sealing it without emptying and purging the tank?

Alan · 23 June 2006, 15:23

Erin,

What is your tank made from? (Sorry if I have missed this in the thread). I had fibreglass fueltank failure on the very first outing with a brand new BWM back in 98. A good few litres of fuel in the bilge and very fortunate that the whole lot didnt go up in smoke! We ended up with the manufacturer replacing the tank with a stainless one which of course involve cutting a bloody great hole in the deck and resealing. Such are the joys of underdeck tanks.

I'm guessing with Prosport changing hands you dont have comeback to the manufacturer so if it is the tank then thats not the best news. I suggest you check and recheck every connection/breather. I also had a fuel leak on Blue Ice shortly after taking ownership which turned out to be a missing gasket from the fuel sender/inspection plate (removed by my engineer for reasons that escape my memory now). This leak only presented itself when the tank was filled to the brim when a combination of pressure and movement caused the leak. That was easily fixed (so dont panic Richard B

) by replacing the gaskets (actually a double gasket set).

You need to isolate whether your problem is the tank itself or connections/breathers. If it is then rectification is unfortunately involve dramatic surgery to your RIB. I'd suggest getting a good boatbuilder/rib specialist involved at this point. As to the merits of fibreglass vs stainless I think this has been debated before and often and I think will come down to your own preference at the end of the day.

Jono · 23 June 2006, 15:32

Quote:

Originally Posted by Alan

..... As to the merits of fibreglass vs stainless I think this has been debated before and often and I think will come down to your own preference at the end of the day.

...yeah... Aluminium

codprawn · 23 June 2006, 15:35

IF it really did come down to it - rather than having to rip up the deck etc would it be possible to get a flexi bag tank in through a smaller hole?

Jono · 23 June 2006, 15:42

...ask t'other Jono.. he'll remember which of the Prosports up there had the problem... and what the fix was.

Soupy · 24 June 2006, 11:18

Had a similar problem with my Zodiac pro open. Stainless steel tank and leeking at top of sender unit. Bottom rubber gasket on sender within tank had gone and was allowing seepage when tank full and under most pressure (as stated above). Had to order a complete new unit as do not sell seperately of course. Installed and new seal disintegrated soon thereafter - probably rotted by the petrol I'm told!! On advice of very good engineer then cleaned everything up and used lots of ordinary silicone sealant on all contact points (this is what they use all the time) before tightning up. Easy enough and not a problem since.

fast fred · 24 June 2006, 12:02

evenrude make suff called M type ( or 3m 847) it's used to seal case halfs, it will not fail,

Erin · 24 June 2006, 20:29

I doubt there's any kind of gasket on the existing setup. It looks like black sikaflex or similar. Will wait until the tanks almost empty then have a closer look.

The tank is fibreglass.

Erin · 17 April 2007, 20:16

Well I eventually got round to sorting this little problem out. i managed to siphon out nearly every drop of petrol into all my jerry cans, even having to make use of a brand new water butt for the last 30 litres

.

Photo 1 shows the plate on the top of the tank (already removed but back resting place for benefit of photo. That was a bu**er to remove!)

Photo 2 shows the hole in th top of the tank cleaned as best I could of old sealant.

Photo 3 shows the various sizes of screws and the old rubber gasket (obviously home made) from the fuel sender. Good old Prosport, why use one standard size of screw when 5 different types can be found in the bottom of your toolbox.

Photo 4 shows my nice new gaskets cut from neoprene reinforced cork.

Hopefully this new arrangement will work. A good dollop of Blue Universal gasket sealant was added for good measure to all surfaces. i also replaced the fuel suction pipe which was a piece of 9mm copper pipe which was slightly undersized for the olive and union. Had to buy a 10m roll of 10mm microbore form B&Q just for 2 feet of pipe. Nevermind, cheap at the price if it works.

Erin