how to trace a fuel leak?

[atlowers]

Help please forum. I am getting a diesel film in the bilge.I have a falcon 23 yamaha 370sti so access is tight to say the least. Anybody have any idea how I can trace the source. The leak has been occurring for last 4/5 months. The steel tank is under the mid cabin and the leak was first noticed shortly after I replaced the forward bilge pump when I was practically laying across the top of the tank. Problem is, the engine was replaced at the same time so it would be a nightmare to remove the tank. I just dont know how to source the actual leak and prove the tank is the problem. The tank is original 1993, would weight on top of tank cause a minute seal leak? What should I do next? Thanks as ever for constructive help.

 

[omega2]

What you could try is soaking up the film with a babies disposable nappie, and then try to isolate the tank area from the engine bay. You could have disturbed the breather or inspection plate on top of the tank maybe. Does the leak manifest after filling? I am assuming that all connections between tank and engine are sound.

 

[oldharry]

One of the best 'tracers' for the presence of diesel is coloured tissue paper: either Tescos fancy loo paper, or last Christmas's 'festive' paper napkins will do nicely. Doesnt really matter as long as it is as the adverts say 'super absorbent'. The colouring in the paper darkens markedly in the presence of any liquid, and will show if there is any trace of diesel.

Clean very thoroughly round any possible leakage point - i.e. anywhere there is a joint in the fuel system. Dont forget banjo bolts, and the gaskets on the filters. Now, using your 'super soft' loo paper, check that each joint is completely dry. Now take the boat out for half an hour or so.

On return, go round everything with the loo paper again. Any leaks will betray themselves instantly by darkening the coloured tissue.

 

[atlowers]

Thanks omega,
[ QUOTE ]
Does the leak manifest after filling? I am assuming that all connections between tank and engine are sound.

[/ QUOTE ]

No its not just after filling, its a constant problem and yes I have tried to check the cnnections. I believe I can isolate the tank from engine bay so will try this.

Old harry,
Thanks for the tip, will try this with the bay isolated and lets hope I can find the source, trouble is, if it is the tank, as the leak is so tiny, not sure wether the cost of repair would be bearable even though deisel costs going through the roof! /forums/images/graemlins/frown.gif



Thanks
Andy

 

[PCUK]

Can you get to the entire top area of the tank?
If so it may be possible in extreme circumstances to cut the top off the tank and fit a new slightly smaller one inside. This idea saves a great deal of money when there are no other alternatives.

 

[makkers]

Having been in a similar position last year I assume that you checked the obvious like fuel lines, filters and all interconnecting hoses to include fuel return.

Does the diesel leak occur when the boat is not in use e.g sat at berth/mooring etc or is it when the engine is running and when the boat is in motion? Or both? This will help in identifing if its a fuel flow issue as opposed to a potential tank issue.

Dont want to scare you but if it is a tank issue then things can get a bit costly. Probably like your boat my fuel tank sits under the mid cabin and I discovered a split along a welded seam at the top of the tank.

My issue goes back about 18 months when I noticed a frequent allbeit small quantity of diesel in the bilge. Initially we thought it was the result of a leaky fuel hose somewhere on the fuel system.

However over time the issue progressed to the point that we identified that the leak was either after we filled up with fuel and or when the boat was not level i.e bow up getting over the hump and cruising pitch. This implied a potential leak in the top of the tank.

Eventually, last summer it came to a head when we noted significant fuel in the bilge to the point that we had leaked at a guess 20+ ltrs in one go.

Anyway to cut a long story short we found a split on the top seam of the fuel tank nearest to the engine. This is your worst nightmare! as the boat is almost built around the tank and tank removal may require significant surgery.

Fortunately the seam split was accessable (just) for a weld repair but did involve the engine out etc. If this was petrol you would have no chance of a weld repair!

Sorted now but I think the seam split was either expedited by years of big waves/chop abuse but also just above the rear of the tank nearest to the engine is the rear bulkhead. Any flex of the cockpit floor above will put pressure on this bulkhead and in turn potentially hit the fuel tank. Although there is about 1/2" between the bottom of the bulkhead and top of the tank this is definatly worth being wary of.

Keep us informed of what you find.

 

[atlowers]

Makkers

Thankyou for the info although some of it a little worrying. I have this dreaded feeling that it is indeed a seam problem on the tank particularly as it started about the time I had been laying all over it replacinc the mid section bilge pump. I have noticed that it happens all of the time, but is more obvious after a run and having come back from Cowes to Gosport in wind over tide couple of weeks ago with a full tank, it is probably at its worst, but this remains a very smal amount. My plan is to firstly isolate the tank section from the engine and mop everything and leave her for one week to see if any leakage occurs. I will also re check all lines and connections as new engine was fitted at same time as I replaced the pump. Really dreading having tank problem after allprobs of previous year so hoping for the best and not having to consider pcuk`s suggestion which sounds horrific.
Thanks again for the advice
Andy