Help! Fuel in bilge - tank out?

Revenger715 · 03 May 2022, 12:36

Typical. Boat has been out of the water for two years since last being used and was serviced just before being put away (planned to use but Covid intervened!).

Looking forward to getting her back on the water I have spent a couple of days pre-season cleaning and could smell fuel, particularly around the back of the boat, today I noticed a drip from open bung and when I checked there was a patch on the floor where something has been leaking. Looked in the bilge and there is clearly a small pool of fuel collecting in there. No obvious leaks from pipework in the bilge (water filter etc).

Tank was brimmed before the boat was stored and now shows maybe 9/10ths so not quite as brimmed as it was, but certainly there has been no huge leak/massive failure but certainly something is weeping / seeping somewhere. She sits on the trailer cranked up so that rainwater flows away to the back drains. At the weekend I cranked it up a bit higher at the front as we were washing the tubes off and conditioning them.

Anything with fuel /boats concerns me greatly! The tank in a 715 looks to come out vertically if you remove the helm/passenger seating without having to chop up decks etc. But still a PITA..!! Boat is 2003 and tank / fuel lines are probably original. Time to bite the bullet and get it all stripped out and replaced? Am I missing anything obvious?

Thank you.

Pikey Dave · 03 May 2022, 16:48

I’m not familiar with the layout of your boat/tank, but..if you brimmed it, would that bring the fuel over the level of the joint between the filler hose & tank? If it was brimmed with the trailer level on the forecourt & then you jacked up the front end, the fuel in the front of the tank would have been at a higher level than the transom. Maybe it’s just weepage.

GuyC · 04 May 2022, 06:40

On a similar path, could the gasket for the sender unit be leaking. If, due to the trim of the boat in storage, the sender unit gasket or one of the other connections has been subject to a slight head of fuel over a prolonged period, it may cause it to leak over time.

I guess one option would be to use the boat to reduce the fuel level and then put it back on the trailer in the same trim. That will at least identify whether the leak is anywhere but the top of the tank.

If the fuel you put in two years ago had ethanol in it, could that be a cause of degradation of the seals?

Chris Caton on here had one so he may be able to assist if you PM him.

TmMorris · 04 May 2022, 15:16

How is the tank sealed from the atmosphere?

Could it be as simple as evaporation/seepage via the breather during expansion events over the last couple of ears of sitting there brimmed?

Revenger715 · 04 May 2022, 19:31

Thanks gents,

It is an odd one as the tank is now not brimmed full (not past the filler, not enough to weep past the breather which is screwed into the top).

I loosened the fuel tank cap so there is in effect now no pressure, set the trailer back to horizontal today and then this evening cranked it right back up and some more fuel came out of the bung, not a lot and towards the end was a bit watery. Not sure whether I cranked the trailer higher than yesterday but maybe a tiny bit.

Could it be as has been suggested, some old fuel which has 'pressured' out of the tank over the last two years and has been sat in the bilges somewhere. But then why did it drain dry yesterday and today some 'fresh' stuff come out.

Don't get me wrong, it is not gushing out but any sign of fuel in the bilge / smell of fuel puts me right off using it!

Annoying!!

TmMorris · 04 May 2022, 20:10

It's perfectly feasible that a brimmed tank over a couple of years would sweat out some fuel, some of which would condense in the bilges. And maybe you've tilted the boat a bit more than last time and just got more of that out. But obviously the concern is that it's not that.

Are you able to really flush the bilges out well with a hose so that you can be sure there is no fuel left in? Then, leaving the boat tilted at a set point, close the bung, pour a couple of litres of water into the dry bilge, leave for a few days and then level the boat, tilt it back to the same position and drain into a container and check for petrol?

If there's none and none again on a second test then you've arguably not got an issue.

Can you recall if you used E5 when you filled it? Do you know if your tank was free of water when you filled? The reason being that after 2 years you might want to empty the tank anyway in case there's a phase separation emulsion that'll block your injectors. If you e got ethanol in your fuel and some water in the tank then phase separation can start to occur after about 6 months.

Revenger715 · 05 May 2022, 15:09

Hi guys, an update.

More was coming out yesterday so I waited until it stopped and then levelled the boat back off on the trailer and left 24 hours.

I've just cranked it back up and a little bit has come out but negligible.

So I'm now thinking there isn't a leak and what has been coming out of the bung is the seepage where the tank has 'breathed' over the last couple of years into the bilge.

What do we think?

Thanks

TmMorris · 05 May 2022, 20:37

It is possible and hopefully the exact issue. Two years of expansion, breathing, evaporation and its plausible for there to be condensates fuel in the bilges.

Can you not completely flush the bilges with fresh water to wash out all current fuel residue and then see if any re accumulates?

Revenger715 · 09 May 2022, 18:07

Thanks, am away from the boat for a couple of weeks now so will see what the position is when I get back, in theory she is all polished and tubes conditioned and ready to get back out to play!!

jakew009 · 10 May 2022, 08:22

This thread has a ‘deja vu’ feel to it after the similar thread on YBW

Personally I’d not mess around if you suspect the tank is leaking. There’s no way a tank should spew 10% of its contents out into the bilge, ever, unless something is wrong with it.

When your 10 miles off shore with your family on board, the last thing you want to do is look in the bilge and realise it’s full of fuel.

Start by replacing the sender unit seal and then pressure test it.

If it still leaks blank off all the fuel hose connections and pressure test again. If it stops leaking replace all the fuel hoses.

If it still leaks, pull the tank out and see what’s going on.

Revenger715 · 10 May 2022, 08:27

What is/where is the other thread?

The sender unit is on the top of the tank though and no evidence at all of any leaks around it.

The offshore with family and fuel in bilges is exactly what I am worried about though.

TmMorris · 10 May 2022, 08:33

My understanding is that while the tank has depleted in volume a potential 10% over two years this 10% hasn't been found in the bilges but rather some of it has.

That's not immediately confirming direct transfer from tank to bilges but potentially suggesting indirect with the bulk being lost. As the tank was left open to breath, from what I can gather, and depending on how the boat was stored for those two years then it's plausible that the fuel in the bilge is from evaporation with part condensation.

I think before taking the very sensible advice of not mucking about with a fuel leak one would want to completely flush out the bilges and leave the boat for a while to see if any fresh fuel collects.

Revenger715 · 10 May 2022, 08:41

The boat has been stored at my South West French place for two years, under it's cover but on an open driveway and succeptible to vast changes in temperature (a lot of heat in the summer!!).

Yep there is definitely not 10% of fuel tank in bilges - each time some has come out (I've cranked the trailer up 3 or 4 times in the previous week or so) there is probably enough to fill a coffee mug, and it is watery.

The tank wasn't left open to breathe. It has a built in breather which pipes into a fitting on the upper left side of the pilot/pasenger seating. I'm not sure that is working though. In a previous storage period a few years back I have found a trace of what looked like oily fuel (?) down the side of the seat from the breather and had to clean it all off from there and the rear floor of the boat. To me, that is when the tank has breathed correctly through the breather but this time around there is no trace of that so perhaps the breather is not working and it has vented out from somewhere else.

The tank is certainly open to breathe now though, I have left the filler cap loose to see what happens.

TmMorris · 10 May 2022, 09:18

You've probably had some pretty big diurnal temp changes going on! Easily enough to evaporate off the more volatile molecules of the fuel blend over two years.

Could evaporation account for almost 10% of the volume? It's plausible. If really brimmed then the first lot could have simply come out as liquid during the initial expansion events.

If you can follow the breather path back to the tank then it might be worth checking that hasn't been damaged by a pressure build up that couldn't be released?

I think that whatever you do you probably need to consider junking all the fuel in the tank and having it cleaned if there was ethanol in there and air was able to get in etc.

jakew009 · 10 May 2022, 21:19

Quote:

Originally Posted by TmMorris

You've probably had some pretty big diurnal temp changes going on! Easily enough to evaporate off the more volatile molecules of the fuel blend over two years. I doubt it will need cleaning unless it was dirty before.

Could evaporation account for almost 10% of the volume? It's plausible. If really brimmed then the first lot could have simply come out as liquid during the initial expansion events.

If you can follow the breather path back to the tank then it might be worth checking that hasn't been damaged by a pressure build up that couldn't be released?

I think that whatever you do you probably need to consider junking all the fuel in the tank and having it cleaned if there was ethanol in there and air was able to get in etc.

I tend to agree - a quick Google suggest it only has a 120l tank so if the fuels 2 years old I’d probably suck it out and then pressure test the tank.

A pressure test is the only way of knowing if it leaks or not… everything else is guessing.

You can use the old fuel up, just check it still looks ok and put 20l in each time you fill up. To be honest I’d probably not even bother emptying it out if it smells ok.. just pressure test it.

TmMorris · 11 May 2022, 06:29

Yup. In the old days, losing the volatiles wouldn't have been the end of the world and you'd have got away with topping up with fresh and then topping up regularly to dilute it all down but these days unless you know for sure that your tank was dry before brimming and that the fuel you put in was absolutely ethanol free then you have the near perfect environment for phase separation.

It takes about 6 months to start at normal temps and pressures so 2 years of being baked and cooled repeatedly pretty much guarantees that if you had both water and ethanol in your tank then you now have an emulsion sludge lurking at the bottom waiting to be sucked up into your fuel feed and causing a host of annoying issues.

Going forward, for any of us with big tanks of fuel, brimming them for winterisation is almost certainly not going to be best practice.

This season may be the first one where we start to see problems during it that are being caused by tanks with water getting brimmed or just left with E10 in them over winter. 6 months is almost enough time for phase separation in colder climes. Most should get away with it but it's right on the cusp.