Weeping fuel drain plug

[Tom Dussek]

The drain plug on my diesel tank on my Westerly is weeping slightly. I was planning on undoing it, letting the fuel drain, then putting a new fibre washer on the plug. Is that the best approach? Or PTFE on the thread? Or both?
Tom

 

[VicS]

The drain plug on my diesel tank on my Westerly is weeping slightly. I was planning on undoing it, letting the fuel drain, then putting a new fibre washer on the plug. Is that the best approach? Or PTFE on the thread? Or both?
Tom

If it is a tapered plug the seal must be made on the threads so a sealant or tape ie the way to go.

If the plug has flanged head which tightens onto a flat surface a sealing washer is required. A fibre washer may be adequate but others will suggest better types of washer.

 

[Freebee]

if the plug has a flanged head then use a bonded seal sometimes called a Dowty washer.

 

[Channel Sailor]

I have never had much success with diesel and PTFE tape myself. Assuming it is a steel tank (not plastic) and a flat sealing surface on both the bolt and the tank, then I would say a freshly annealed copper washer would be the proper fire resistant method. Use a new washer each time the drain plug is undone. Check the mating surfaces are not burred or scratched in anyway. If the surfaces are damaged then carefully clean up with fine Wet and Dry on a at flat hard sanding block for the tank and a steel penny flat washer with wet and dry paper (with a hole in it) on the bolt mating surface. Easier is a fibre washer or I have used a Polythene looking washer on a low pressure diesel union as a temporary repair, but some would say not fire resistant and possibly not allowed on inland waterways for that reason. If it is threaded surfaces that make the seal or a cone shaped seal surface, then sorry I do not know. If the tank is plastic/Poly prop something or another then maybe a Vetus catalogue could offer some ideas as they make a nice plastic tank and fitting. I vaguely recall my yacht's Vetus poly prop tank has a hard ish plastic screw fitting possibly with some kind of rubber looking washer, but not sure as I cannot remember clearly when I last took it off.

A Dowty washer still needs perfect mating surfaces. I seem to remember the washer surface on a Dowty type washer is steel (the ones I have seen were) . Copper is softer so would seal with less torque. I don't see the point of Dowty washers in this situtaion. But hey, I am just boat owner not an engineer.

 

[Amlov]

It would be slightly surprising if it has suddenly started to leak. Could it be that the tank has rusted through around the weld on the drain plug fitting?

 

[Freebee]

A bonded seal is a type of washer used to provide a seal around a screw or bolt. Originally made by Dowty Group, they are also known as Dowty seals or Dowty washers.[1] Now widely manufactured, they are available in a range of standard sizes and materials [2][3][4]
Dowty Seal taken over by Trelleborg sealing solutions. Bonded Seals are made by Trelleborg in the United Kingdom to the original specification.
A bonded seal consists of an outer annular ring of a hard material, typically steel, and an inner annular ring of an elastomeric material that acts as a gasket. It is the compression of the elastomeric part between the faces of the parts on either side of the bonded seal that provides the sealing action. The elastomeric material, typically nitrile rubber, is bonded by heat and pressure to the outer ring, which holds it in place. This structure increases resistance to bursting, increasing the pressure rating of the seal. Because the bonded seal itself acts to retain the gasket material, there is no need for the parts to be sealed to be shaped to retain the gasket. This results in simplified machining and greater ease of use as compared to some other seals, such as O-rings. Some designs come with an additional flap of rubber on the internal diameter to locate the bonded seal at the centre of the hole, these are called self-centring bonded washers[5]

 

[Freebee]

loctite 577 thread sealant is very good with fuel leaks on threads I have used it m,any times on diesel and kerosene

 

[Tom Dussek]

Thanks everyone. (It's leaking because I disturbed it, thinking I'd see if there was any crud to clear when I first got the boat. There wasn't, happily, but there *is* now a leak. That'll teach me for trying to be responsible.)