Sealing my fuel filler

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pcatterall

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We had a pint of water in the starboard tank over winter and none in the port tank. Both deck fittings had been cleaned and had new seals last year.
Unfortunately we have low gunnels so water can sit over the fillers though next winter i will ensure boat is loaded to the stern where the drains are.
I have considered using off tape on the threads but perhaps just grease and rely on the seals is best, over winter perhaps I could use a silicone film on the top of the fitting .
Any ideas will be appreciated. It wasn't​ just the water issue but the effect on the diesel ( which went black and would not settle out or clean through the polishers and had to be dumped )
 
If grease on the threads AND a new seal hasn't worked then perhaps the filler cap unit is knackered or the water is coming in elesewhere in small quantities.

A pint is too much to be condensation.

Can you access the breather pipe ? If yes, some washing up liquid sprayed around the filler cap and blow down the breather. That will gently pressurise the tank and the filler tube. If there's a leak, the bubbles should show you where.
 
sarabande said:
Can you access the breather pipe ? If yes, some washing up liquid sprayed around the filler cap and blow down the breather. That will gently pressurise the tank and the filler tube. If there's a leak, the bubbles should show you where.
Click to expand...

+1
It's easy enough to check it out in this way rather than systematically replacing bits until you find the culprit. Depending on the type of breather, a dinghy pump might be adapted to lightly pressurise the system.
 
pcatterall said:
We had a pint of water in the starboard tank over winter and none in the port tank. Both deck fittings had been cleaned and had new seals last year.
Unfortunately we have low gunnels so water can sit over the fillers though next winter i will ensure boat is loaded to the stern where the drains are.
I have considered using off tape on the threads but perhaps just grease and rely on the seals is best, over winter perhaps I could use a silicone film on the top of the fitting .
Any ideas will be appreciated. It wasn't​ just the water issue but the effect on the diesel ( which went black and would not settle out or clean through the polishers and had to be dumped )
Click to expand...

If the filler cap is in good condition and you've replaced the O-ring and used plenty of silicone grease then it should not let in water. You seem to have done the necessary with the filler but have you checked the vent arrangement? I have read several reports where heavy rain and wind from a certain direction and with the boat at a certain attitude, can enter the tank vent or its hose.

Richard
 
Good point RichardS. My assumption was that the breather pipe was properly installed and functioning.
 
Agree, Richard. The OP's maybe become a little over-focussed on the filler, but the pressure test should clear that up one way or the other. Breather pipes should ideally be bent to make a goose-neck for precisely the reason you describe (not to mention whilst heeled at sea). It's worth the OP's checking this.

P.S. The OP may have reason to believe the water accumulated over the winter, or has he just assumed it?
 
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Notwithstanding the good advice given, the OP doesn't actually say he used grease, just that it might stop water ingress.

So i'd have two questions, was grease actually used and as Mac asked, did the water accumulate over Winter, for sure ?

I would then check the seals as suggested, before adding grease and rechecking (if grease was not already used.
 
Relying on grease to do the actual sealing is a bad idea, it will have diesel around it, it may get washed out.
Is the seal in the right place?
Is it the right size O ring?
Is it working between two surfaces that are in good order?

The grease or oil should just be there to allow the rubber seal to slide between the two parts of the filler as the cap is screwed in.
 
lw395 said:
Relying on grease to do the actual sealing is a bad idea, it will have diesel around it, it may get washed out.
Is the seal in the right place?
Is it the right size O ring?
Is it working between two surfaces that are in good order?

The grease or oil should just be there to allow the rubber seal to slide between the two parts of the filler as the cap is screwed in.
Click to expand...

Check out posts #2 and #4 again .... "If the filler cap is in good condition and you've replaced the O-ring ....." etc ;)

Richard
 
We had a similar concern and a fellow owner had a £2k bill after water seeped into the diesel long term through a micro leak in a deck filler. I then discovered the Vetus right angle filler designed to go in the side of a combing or in our case wheelhouse. Zero chance of water getting into the diesel. I suspect, but obvs have no proof, that a large percentage of water-in-the-fuel issues are due to seepage through deck fillers.
 
RichardS said:
Check out posts #2 and #4 again .... "If the filler cap is in good condition and you've replaced the O-ring ....." etc ;)

Richard
Click to expand...
But has the o ring been replaced with the right thing in the right place?
Did the previous owner perhaps fit an o ring that was handy, when the cap was designed to have a big flat rubber washer?

It may even be worth checking it's the correct cap for the filler, perhaps the original is on the seabed somewhere and the nearest thing from the nearest chandlers has been fitted?

A pressure test is a good idea.

Yacht fllers / 'deck plates' are often rubbish compared to the filler cap on a car, which has a much easier life!
 
lw395 said:
But has the o ring been replaced with the right thing in the right place?
Did the previous owner perhaps fit an o ring that was handy, when the cap was designed to have a big flat rubber washer?

It may even be worth checking it's the correct cap for the filler, perhaps the original is on the seabed somewhere and the nearest thing from the nearest chandlers has been fitted?
Click to expand...

Good grief .... there would be no end to suggestions for the possible cause of a problem if we followed that approach. However, I'm game if you are ..... but we'll need a lot of spare time on our hands. :D

Richard
 
RichardS said:
Good grief .... there would be no end to suggestions for the possible cause of a problem if we followed that approach. However, I'm game if you are ..... but we'll need a lot of spare time on our hands. :D

Richard
Click to expand...

Well if water's getting in, it's either leaking in, coming in with the fuel or some malign person is adding it?

I bought an old motorbike which didn't run years ago. The seller knew there was water in the fuel and told me that. I never found out if he knew about the sugar that was in there!

Wasn't there a thread about this years ago, somebody found water was getting between the filler and the deck, then running between the filler and the hose?
Never underestimate people's ability to put things together wrong!
 
I had a water in fuel issue last year, the wrong Oring under the filler cap, replaced with correct. As a belt and braces action, I put Gorilla Tape over the top so making an xtra seal. Has worked so far and has stayed stuck until removed.
 
Thanks all. I did change the o rings 2 years ago, the old seals were perished beyond identification so i had to guess the size. However there were no leaks over winter in Sardinia the previous year and the boat had been left ashore at an angle that meant rain water sat on top of the filler for the whole season despite my instructions and drawings showing them to tilt her back a little.
I will try all the tricks recommended to source any leaks and probably belt and braces with tape or silicone over the seal as well.
I will also do a more thorough pre season check and use our fuel polisher to check fuel state before even starting up.
Cheers
 
I suspect filler cap leaks accounts for the vast majority of water in fuel situations, and the foru goes on endlessly about dealing with that.

Good advice as usual - thick non bio degradable grease on the threads, just wear some disposable gloves when filling.

For the Winter puddle, I would suggest a large dollop of plasticine shaped over and around the filler to form a solid mass that seals the filler cap inside. It can easily be removed when you want to use the boat.
 
I have a double cap.
The normal filler is set in the side deck. Around that is a ring of ply sika'd on and screwed. Over that is a standard grey 4" soil pipe access plug screw cover - with the threaded ring cut to about 1" high and screwed to the ply - then sealed,
My problem was standing water pooling around the filler. The cap is totally waterproof - and has a sealed 1" upstand. It unscrews easily ( does not need to be tight ) - then the brass filler plug below is used as normal.
Ridiculous place for a filler plug - but thats where the surveyor wanted it. I originallly had it under the cockpit seat !
 
Can't claim that the problem is solved but fingers crossed. I investigated the filler to tank situation by almost climbing into the deep locker! Rather than the expected pipe direct from the deck fitting to a neck on the tank i found that a sort of box pipe was glassed from the tank up to the underside of the deck with the short neck of the filler locking down into it. It was possible for water to get into the box section by finding its way under the filler cap flange. I lifted out the filler unit and it did look like there may have been water ingress. I took the opportunity to test the filler seal by filling the inverted unit with fuel and sitting it on some kitchen roll for the day. I then rebedded the unit and will cross my fingers.
Thanks for the good advice!
 
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