Insulating the diesel tank.

graham

graham

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To reduce the issue of condensation allowing water into the diesel tank would insulation help?

After spotting early signs of fuel bug I replaced the tank and pipework which was donkeys years old and needed changing anyway.

Now have a tank with an inspection/cleaning hatch ,the tank can be easilly disconnected and removed from the boat for cleaning as part of annual refit M16 also being used.
 

pvb said:
I don't think insulation would make any significant difference. Extending the length of the breather pipe might help.
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The breather is currently about a meter long 19mm rubber fuel pipe.With a little bit of work could add another meter in length if that would make any difference? What is the theory behind this?
 
graham said:
The breather is currently about a meter long 19mm rubber fuel pipe.With a little bit of work could add another meter in length if that would make any difference? What is the theory behind this?
Click to expand...

How does moisture get in to the tank? Answer: via the breather pipe.

What's the mechanism by which moisture is drawn in? Answer: expansion and contraction of the air in the tank moves air through the breather pipe. With a short breather pipe, there's more chance of damp outside air being drawn in to the tank.
 
pvb said:
How does moisture get in to the tank? Answer: via the breather pipe.

What's the mechanism by which moisture is drawn in? Answer: expansion and contraction of the air in the tank moves air through the breather pipe. With a short breather pipe, there's more chance of damp outside air being drawn in to the tank.
Click to expand...
That makes sense. .tbh I think re fuel I have gone from a bit of string holding my trousers up to belt braces and elastic! I can easily extend the breather so will do that then relax .
Cheers
 
The breather should be fairly straight.
Otherwise it will tend to collect fuel in any dips, then this will be blown over the deck when you fill up.
Most of the alleged 'condensation' in fuel tanks is really water leaking through the deck filler.

If you wanted to reduce condensation, you could lead the breather through a chamber of silica gel or other water absorber, but you might want to open a bigger breather while filling.

The best thing is to have a tank with a small sump to collect the water, or draw fuel from the very bottom of the tank so the water is not allowed to lie in contact with the fuel.
 
I would suggest also check the deck filler cap regarding o-ring etc
The common 'flip up handle' type sometimes has an unsealed hole for the axle situated under the o-ring when cap is screwed down. Will let in a small amount of water into the tank with every rain shower or wave on deck.
IMG_6832.JPG.jpg
 
hmm, this idea of water getting in through the deck filler is making me think about my fuel tank. I've never had an inboard diesel before, just petrol outboards and carry on tanks.
I can't imagine that i will be filling up at the marina very often with a 1gm10, more likely that I will be buying Tesco diesel in a 5 litre can and adding some kind of bugbuster stabililiser to help with the biofuel component, so why have a potentially leaky deck filler when I could just put it straight into the tank from a jerrycan, and cap it there.
 
Dellquay13 said:
hmm, this idea of water getting in through the deck filler is making me think about my fuel tank. I've never had an inboard diesel before, just petrol outboards and carry on tanks.
I can't imagine that i will be filling up at the marina very often with a 1gm10, more likely that I will be buying Tesco diesel in a 5 litre can and adding some kind of bugbuster stabililiser to help with the biofuel component, so why have a potentially leaky deck filler when I could just put it straight into the tank from a jerrycan, and cap it there.
Click to expand...

You could certainly do that, but there's no reason why a deck filler shouldn't be properly sealed. Check/replace the O-ring, smear with silicone grease.
 
I have been using Tesco diesel for over 25 years and never had a problem with either water in fuel or bugs. In fact I left about 20l in the tank when I laid up the old boat in 2010 and before I recommissioned in 2019 I pumped it all out with a Pela and no sign of any water or debris. Did not bother to drain the pipes and engine started first press on the fuel in the system and ran perfectly, picking up the new fuel.
 
I have 2 steel diesel tanks welded into the hull of my steel boat and live in the subtropics with very high humidity in summer.

I have never had and water in my diesel tank as I use a water detecting paste when I add fuel.

My vents have a gauze preventing any water getting and my fuel fillers are on a raised section in my cockpit with caps that cover thus shed any water once the cap is refitted.

Never could understand how condensation could get into a proper fitted tank.
 
TernVI said:
The breather should be fairly straight.
Otherwise it will tend to collect fuel in any dips, then this will be blown over the deck when you fill up.
Most of the alleged 'condensation' in fuel tanks is really water leaking through the deck filler.

If you wanted to reduce condensation, you could lead the breather through a chamber of silica gel or other water absorber, but you might want to open a bigger breather while filling.

The best thing is to have a tank with a small sump to collect the water, or draw fuel from the very bottom of the tank so the water is not allowed to lie in contact with the fuel.
Click to expand...
I have often toyed with the idea of incorporating silica gel or similar into the breather, but it would have to be arranged in such a fashion as not block up and would have to be removeable in order to reactivate the dessicant. Those little anti-condensation cushions for your car, with the dot that goes pink when damp might hold some potential.
 
Dellquay13 said:
hmm, this idea of water getting in through the deck filler is making me think about my fuel tank. I've never had an inboard diesel before, just petrol outboards and carry on tanks.
I can't imagine that i will be filling up at the marina very often with a 1gm10, more likely that I will be buying Tesco diesel in a 5 litre can and adding some kind of bugbuster stabililiser to help with the biofuel component, so why have a potentially leaky deck filler when I could just put it straight into the tank from a jerrycan, and cap it there.
Click to expand...
The last thing you want is even a tiny amount of spillage.It stinks and can be hard to clean up if it gets into.inaccessible places in the bilges.
 
graham said:
The last thing you want is even a tiny amount of spillage.It stinks and can be hard to clean up if it gets into.inaccessible places in the bilges.
Click to expand...
maybe I'm fixing a problem that doesn't exist, but options are there if I do find water in the tank in future.

I'm looking at forums for equipment I've never owned before in 20+ years of boating, and seeing when things go wrong, not how they work just fine most of the time.
 
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