Fuel tank breather

Cornishmuttley

Cornishmuttley

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My plastic (or similar) diesel tank has a breather tube that had no 'end', it just had a loop with the top end tied to the underside of the cockpit coaming (like that when I bought the boat). SWMBO does not like the smell of diesel which now permeates the boat (until aired through) and wants some action to resolve the problem. Actually the smell does get a bit much. In addition to blocking up holes forward from the aft locker, should I:
1. clamp the end to stop fumes (or will this choke the engine)
2. drill a hole in the cockpit and fit a two way valve of some sort (least preferred option)
3. some other solution that I hope you will come up with ('scuse the poor grammar)
I have not seen a breather on other tanks and am wondering if it really is necessary.
 
Cornishmuttley said:
My plastic (or similar) diesel tank has a breather tube that had no 'end', it just had a loop with the top end tied to the underside of the cockpit coaming (like that when I bought the boat). SWMBO does not like the smell of diesel which now permeates the boat (until aired through) and wants some action to resolve the problem. Actually the smell does get a bit much. In addition to blocking up holes forward from the aft locker, should I:
1. clamp the end to stop fumes (or will this choke the engine)
2. drill a hole in the cockpit and fit a two way valve of some sort (least preferred option)
3. some other solution that I hope you will come up with ('scuse the poor grammar)
I have not seen a breather on other tanks and am wondering if it really is necessary.
Click to expand...

to get fuel out of the tank the volume drawn off must be displaced with air.
therefore a breather is req.
why not vent o/b
 
1. Clamping the end will eventually starve the engine of fuel, unless there is another route in for air. ( or the plastic tank will collapse)

2. not sure what you mean

3. Extend the tube to a proper tank breather outside.


I am surprised that the vent you describe is sufficient to cause the smell. Are you sure there are not some very small leaks somewhere?
 
I would be very surpised if enough diesel fumes escape from a breather pipe to cause a noticeable smell. Mine is vented to a small fitting with a gauze strainer at the end just outboard of the cockpit.

I would also suspect a leak of liquid diesel, does not take much to be unpleasant.

As others have said, if no breather either the engine stops or your tank implodes. :eek:
 
Obviously without a detailed idea of the exact layout/space etc in the cockpit coaming it's difficult to know how much room you have to play with and what would be possible.

The normal arrangement for tank breathers led into the voids/undersides of cockpit coamings is a straight or 90% chromed brass breather with a 12mm tail... exiting on the deck side of the coaming if possible. These are widely available, see straight version below.

13524_lg.jpg
 
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is the smell really bad after you have filled up? That is when all the air (smell) in the tank gets displaced out the breather, if it ISN'T significantly worse after a fill up, i would suggest its a leak somewhere too.

Either way, it would have to be considered "best practice" to vent overboard.
 
I thought the breather was there to stop the fuel hoses being blown off when you filled up with fuel. For this reason the breather has to stay and shouldn't be clamped. Your choices seem to be to live with it or fit a through hull breather to vent the tank outside of the living area.
 
You really should not be getting any noticeable diesel smell from the breather. The breather is a vital part of the system, and tanks have to have one, or as the fuel level drops an increasing level of vacuum is created. This will stop the engine once the pumps are unable to draw fuel against the vacuum. So no, you cannot close or clamp it off. If you are sure thats the problem, then extend it so it goes O/B away from the accomodation, but dont position it so that water coming aboard can get into it! Turning it into a vented gas locker might be a solution.

It only takes a small amount of diesel to smell, so any spill during filling will make matters worse. A good diesel installation should not smell except when the fuel system has been opened for servicing (filters etc), or if there is diesel lying in the bilge. If the smell is bad enough to upset people, then there is something wrong somewhere: minor fuel leaks are the obvious cause, specially in the fuel return line which does not affect the running of the engine. Tracking them down is difficult, but coloured soft tissue paper (Tescos best pink loo paper does it quite well!) can be used to wipe down all the joints and pipework. The colour goes much darker when moistened, making it easier to spot leaks. Is the tank OK? It only needs a seam to be weeping for the whole boat to stink! Same goes for the filler arrangements - is the filler pipe 100% fuel proof?

The other possible cause is diesel spillage residue from changing the filters. If that has got into the bilges, or on to woodwork it can be quite difficult to kill the smell. A scrub with a good quality bilge cleaner, and thorough rinsing out is needed
 
I'd agree with responses above.

Don't block breather but ideally route it outside (making sure water won't get into the boat or the tank of course).

Smell is more likely slight seepage. Usually from a filter, occasionally from a pipe joint.

Pink toilet paper is a good way of detecting leaks as the colour changes a bit when damp with diesel. I'd wipe round the pipe joints and the filters. There should be aboslutely no seepage. Any seepage really smells.

On my boat the cause was the seal on the secondary filter.
 
thank you

Thank you for the replies. Clearly I have to buy some pink paper (where did I put that disguise) and clean up everything that comes near the diesel. As the tank is plastic (?) see through variety I had obviously better not cut off the air and induce an implosion. Now, where are those marigolds?

I may go the route Saxonpirate suggests with the addition of putting the vent in the back locker which is already vented.
 
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My fuel tank (a steel one under the stern deck of my Atlanta) is just vented by a short length of copper tube up then along from the top of the tank. The only time I've had any smell from it was when I overfilled the tank. I wonder if your plastic vent pipe is of too large a diameter encouraging an exchange of fresh air with tank fumes otherwise, as suggested by previous posts a slight leak somewhere seems possible.
 
The best place for the vent is overboard, ideally high on the transom near the center. This will keep it out of the water in all circumstances. It shouldn't ever be vented to a locker or any other part of the interior of the boat.
 
Overfilling

TamarMike said:
My fuel tank (a steel one under the stern deck of my Atlanta) is just vented by a short length of copper tube up then along from the top of the tank. The only time I've had any smell from it was when I overfilled the tank. I wonder if your plastic vent pipe is of too large a diameter encouraging an exchange of fresh air with tank fumes otherwise, as suggested by previous posts a slight leak somewhere seems possible.
Click to expand...

I also managed to get a diesel smell in my aft cabin after overfilling a plastic tank. Stupidly, I expected the diesel 'cut off' on the handle to stop when my tank was full. As it is plastic it just expanded under the bunk until the seal on the eberspacher outlet started leaking. It took ages to release about two litres of fuel before the tank shrank back to normal size but the seal continued seeping diesel. Very kindly and good advice from Geoff at Swanwick Marina informed me that the eberspacher rubber seals were not brilliant and he even gave me a square of cork to use as a relacement seal. Lesson learned but I now worry about leaving a space in the tank for the dreaded diesel bug to grow!!
 
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