Sealant for metal to plastic diesel tank joint

[[3889]]

Any recommendations for something for this job? Preferably something readily available in France. My Webasto fuel take off is leaking at the tank. I can get Sikaflex 291i. Is this any good?
Also, is it best to allow sealant to cure before tightening retaining nut (which is independant of metal plate) or tighten things up when still gooey?
TIA
Andy

 

[PaulJS]

I suspect that you're describing a plastic fitting into a metal tank, so my suggestion would be to use a proprietary gasket engine gasket sealant such as hylomar or hermetite, or the French equivalent.
The normal method is to apply a thin film to both surfsces and allow it to go tacky before tightening - in the case of a plastic fitting - very carefully.

(The usual method out here would be for one of my mechanics to wrap the union in about 10 layers of thread tape and then graunch it up until the threads are completely stripped, then when it still leaks to tell me "Chief, it was fine before, it must have been one of the Indians"...)

 

[[3889]]

It's a metal disk, as in this piccy, which is mounted onto a plastic tank. I (think I) realise now that the nut I referred to in my 1st post only compresses an olive sealing the pipe as it passes through the disk - the whole thing is held onto the tank only by sealant of some sort, there seems to be no mechanical attachment. I assume, in these circumstances, gasket compound will not suffice?

 

[capsco]

That looks like an eberspacher pick up in which case it will have a flat section on the edge of the large plate, if so, the correct size hole will allow insertion into the tank to make a "sandwich" joint tightened up by the large nut.

 

[pvb]

It's a metal disk, as in this piccy, which is mounted onto a plastic tank. I (think I) realise now that the nut I referred to in my 1st post only compresses an olive sealing the pipe as it passes through the disk - the whole thing is held onto the tank only by sealant of some sort, there seems to be no mechanical attachment. I assume, in these circumstances, gasket compound will not suffice?

These fuel pick-up pipes usually have a mechanical attachment in the form of a clamp, with a metal washer inside the tank and a metal washer outside the tank, clamped together by a nut. A rubber washer provides the seal. Here's a diagram of an Eberspacher pipe...

 

[jwilson]

Had a major problem for a long time with similar fittings on a Jeanneau tank. The problem is the tank materials is fairly thin and flexible, allowing some movement as the tank flexes. The oblong-with-round-edges washer that goes inside the tank distorts the tank plastic, making the leakage problem worse.

Sikaflex 291 did not work, nor did various other gasket sealers. Have finally got a seal on this and other tank pipe fittings with 2mm cork/nitrile gasket coated with Hylomar red setting-type gasket compound, though the first go with this combination failed, the second try worked. I also had a tiny weep from an olive joint, a trace of non-setting blue Hylomar plus a new olive sorted this.

 

[[3889]]

Had a major problem for a long time with similar fittings on a Jeanneau tank. The problem is the tank materials is fairly thin and flexible, allowing some movement as the tank flexes. The oblong-with-round-edges washer that goes inside the tank distorts the tank plastic, making the leakage problem worse.

Sikaflex 291 did not work, nor did various other gasket sealers. Have finally got a seal on this and other tank pipe fittings with 2mm cork/nitrile gasket coated with Hylomar red setting-type gasket compound, though the first go with this combination failed, the second try worked. I also had a tiny weep from an olive joint, a trace of non-setting blue Hylomar plus a new olive sorted this.

This sounds like my problem. It is a Jeanneau tank. I've seen some recommendations on the Jeanneau owners forum for various substances, none of which seem to be available in Europe so I will give your recipe a go. Thanks to everyone for your input.
Andy

 

[PCUK]

Sealant probably won't effect a cure. You need a mechanical seal. Washers on the inside and outside and a gasket made of nitrile rubber on the inside and outside.

 

[nigelmercier]

I asked the makers of Hylomar which sealant to use, then bought it. It appeared to be normal silicone caulking.

 

[jwilson]

Sealant probably won't effect a cure. You need a mechanical seal. Washers on the inside and outside and a gasket made of nitrile rubber on the inside and outside.

One of my attempts to seal used a 2mm nitrile rubber gasket, worked for a few months but eventually the rubber became soft and slimy, and started to leak. Was bought as diesel-proof gasket material - either it was mis-sold or the biofuel content in modern diesel was attacking it. So far anyway the cork-nitrile gaskets are holding up.

You are right though that you need a mechanical seal: absolutely nothing will stick to the polyethylene that Jeanneau plastic tanks are made from.

 

[David2452]

Have to say I now refuse to fit standpipes to thinner plastic tanks unless I can get a larger backing plate in through an ispection hatch. Though it does work with heavier walled tanks, as has been said, the contact area of all standpipes (Webasto, Eber, Mikuni, Wallas are the same) are too small and the flexing of thin tanks causes leakege after a time when the tank is full. I have had numerous complaints from customers of units either dealer or factory fitted pipes like this and its always the devils own job to recify permenantly, most good sealants work for a time but as soon as the boat is used in anger for a while the problem returns to some degree even if its only a weep. The most succesful method with a plastic tank is to have a threaded boss hot air welded on and screw in the standpipe designed for external insertion.

 

[jwilson]

Have to say I now refuse to fit standpipes to thinner plastic tanks unless I can get a larger backing plate in through an ispection hatch. Though it does work with heavier walled tanks, as has been said, the contact area of all standpipes (Webasto, Eber, Mikuni, Wallas are the same) are too small and the flexing of thin tanks causes leakege after a time when the tank is full. I have had numerous complaints from customers of units either dealer or factory fitted pipes like this and its always the devils own job to recify permenantly, most good sealants work for a time but as soon as the boat is used in anger for a while the problem returns to some degree even if its only a weep. The most succesful method with a plastic tank is to have a threaded boss hot air welded on and screw in the standpipe designed for external insertion.

You are right - my Jeanneau tank was fine until one of the fuel line in/out attachments (not the Eberspacher one) was removed and replaced: from then on it leaked whenever the tank was full and the boat was sailing, whatever sealant was used, as the mechanical attachment for the fuel in/out fittings were four large self-tappers. Once undone impossible to get a good grip again with self-tappers. Eventually gave up and cut a circular hole for a Wema inspection hatch, so I could get machine screws and nuts and washers inside to bed down the fittings properly. That fixed one leak, but introduced another worse one, as the Wema hatch leaked. They may work in rigid tanks, but don't try one in a relatively flexible plastic tank.

Current fix is a six inch rectangular 5mm alloy plate over the circular inspection hole, bedded down onto cork-nitrile with Hylomar red, using about 24 big self-tappers around the edge. If the self-tappers fail I have a Plan B for captive bolts/nuts and an inside backing plate, but so far the (undisturbed) self-tappers are working.

Plan C is to make up an even bigger top plate in 5/6mm alloy, with new holes for the fuel in, out, Eberspacher and fuel gauge fittings and an inspection hatch, big top plate held on with many bolts/nuts/washers.

Plan D is to spend serious money with Tek-Tanks and throw away the Jeanneau tank. It is such a complex shape though that a new steel or thick welded plastic one will be expensive to make.

 

[Melleman]

Have a ss tank made.(we had)
End of stinking nights at the boat mutch safer.
A bit pricey tougth.

 

[cliff]

Any recommendations for something for this job? Preferably something readily available in France. My Webasto fuel take off is leaking at the tank. I can get Sikaflex 291i. Is this any good?
Also, is it best to allow sealant to cure before tightening retaining nut (which is independant of metal plate) or tighten things up when still gooey?
TIA
Andy

OK, What you need is a cylinder flange or "Essex" flange
See this link and scroll down to Cylinder flange http://www.bes.co.uk/products/107a.asp#7560#
Cylinder flanges can be fitted from one side, are designed for thin, flexible tanks and with a little enginuity a 15mm coulld be adapted to take your diesel standpipe.