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Beneteau 393
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Just pulled my fuel tank sender from the PTFE plastic fuel tank. Previous people had put a sealent compound obviously to stop a leak and managed to add plenty to the fuel tank like confetti at a 1960's wedding.

If the supplied gasket is not leakproof (I have to fill the tank and shake the boat) what should I use to seal/bed the sender?



Thanks,


Mark
 

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I've used an orange colored engine gasket material that comes in a squeeze tube. Maybe it's silicone based. Seems to work fine. Last time I cleaned the tank there was no confetti or other party favors.
 
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Your tank is probably UHMWPE (a polyethylene) if its 'plastic'. Like PTFE these polymers have very low surface energy, thus most 'sealants' will not 'stick' to the surface. Without the ability of any sealant to 'stick' to the surface most leaks will be caused by 'capillary action' between the mating surfaces.

What you really need for such application is a soft 'gasket' of a material that is compatible with the modern blends of diesel fuel (and so-called bio-fuels) such as Viton® Rubber or "Santoprene™" (a foam polyethylene) at a 'softness' value of 40 to 50 'durometer'. Such will also need a 'sister plate' on the inside of the tank opening which will prevent flexure of the tank material AND flexure of the flange of the sending unit ... so that only mechanically FLAT surfaces come together, not 'flexed' surfaces which always leak on tanks.
Once you can insure 'flat' of the mating surfaces when drawn together by 'bolting', etc., then common RTV automotive (fuel) sealants can be used to 'fill' the small spaces and surface irregularities that allow 'capillary action' leakage.
The above is a total fix, you may 'get away' with just a progression of segments of the outlined 'steps'.

A pic of the present installation would be helpful.
 

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Ultra blue 'can' work on polyethylene.
Id recommend to first treat the tank surface to be 'sealed' with something like: 3M Scotch-Weld™ Structural Plastic Adhesive DP8005 or other 3M 2-part acrylic based LSE adhesive, etc., let fully cure; THEN apply a Permatex RTV such as Ultra BLUE between the Scotch Weld and the tank sender flange.

Successful 'gluing' of polyethylene is only recent ... Id suggest calling 3M or Permatex' adhesive group's application engineering dept. for the latest info.
 

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Ultra blue 'can' work on polyethylene.
Id recommend to first treat the tank surface to be 'sealed' with something like: 3M Scotch-Weld™ Structural Plastic Adhesive DP8005 or other 3M 2-part acrylic based LSE adhesive, etc., let fully cure; THEN apply a Permatex RTV such as Ultra BLUE between the Scotch Weld and the tank sender flange.

Successful 'gluing' of polyethylene is only recent ... Id suggest calling 3M or Permatex' adhesive group's application engineering dept. for the latest info.
While I agree with this, I doubt it will be easy to find in the islands. Don't forget our friend is not down the street from a industrial chemical supply house. I think going over the surface with what ever mild solvent with a scotch bright and trying the Blue RTV (should be available just about anywhere as it is used on automobiles frequently) should work, and should not be too difficult to "undo" if need be. I have had the best success with RTV when I have used it fairly liberally, and very loosely tightened down the screws, just till it start to oose out then let it sit for a few days before doing the final tightening.
 

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Just a word of caution, most rtv silicone sealants ( basic blue permatex etc) are not suitable for solvent environments. They are fine for oils, but will break down when exposed to fuels. It happens much faster with gasoline, but diesel will break down the sealant over time.

There are fuel safe rtv sealants available- just make sure it states fuel safe on the packaging or you'll be revisiting this issue in short order
 

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One of None
Hunter 34
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If the tank sender is round can you just put an o ring under it?
 
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