sealant for poly tanks - one last time

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Ray400

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Tournament 192
I have a 2000 tournament 19 with a poly tank and I have pretty much reached my limit on water intrusion again and again
I have been using 2 6 gallon portable tanks but it really cuts down my range and I recently ran out of fuel the other day out on the water ..

I recently brought the boat to a yard for engine work and I was told there is no way to seal the sender from water intrusion because the tank is now concave it that area and water will always pool in that spot.
There is a recent sender installed with a very solid rubber gasket at the moment with the screws fastened tightly
I am ready to try anything at this point maybe making a collar to raise the lip/seal it completely and log time on boat for fuel usage/ without a solid sealant for poly these are all a waste of time I fear
thoughts anyone ? - im sure this has been discussed over the years -- perhaps there is a new sealant I am unaware of for polyethylene ?
tnx guys RQ
 
I would also use a Permatex fuel safe gasket maker on both sides of the gasket. Be careful you done strip out the screw holes ovrtightening.

www.permatex.com

Permatex®Fuel Resistant MotoSeal® Gasket Maker, 2.7 OZ - Permatex®

Permatex® MotoSeal® forms a tough, flexible bond in 20 minutes, ideal for motorcycle case halves and carburetor gaskets.
www.permatex.com www.permatex.com
 
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Ray400 said:
I am ready to try anything at this point maybe making a collar to raise the lip/seal it completely and log time on boat for fuel usage/ without a solid sealant for poly these are all a waste of time I fear
Click to expand...
If your poly tank is in good shape you may try to fix the water poodle problem and thats happen not only on poly tanks, often also on aluminum ones too.
I still wonder why manufacturers don't make the tank top slightly convex so that water would run away from top of tank.

However, obviously first thing to do is seal the deck so that no water get on top of the tank, mostly thru a bad sealing pie plate.
Second to a collar for stripped fuel sender screws to make the space around the hole more rigid but if still concave water will still poodle there.

My dive panga in Costa Rica had a black Mueller pre 2006 poly tank and fuel sender was leaking fuel out and water in.
Surprisingly we could glue the fuel sender in place using JB Weld, even if JB Weld on first sight becomes to hard and will separate from poly tank.
But it worked, and worked for many years as only solution would have been to cut the deck to replace fuel tank.
You may give it a try to glue on the fuel tank a thin maybe 5x5 size plate of aluminum/SS with rounded edges using 5200 and fuel sender goes on top of it.
If you wan't you can make a collar to rise the fuel sender, maybe tig welded on the plate i described above, but still would need to seal the collar on the flexible fuel tank plastic.

If poly tank is in doubtful condition i would just replace it, then you should be fine for the next 20 years.

Chris
 
Over tightening the sender screws can distort the flange and cause leaks. This especially true if you use a gasket sealant and overtighten. That can cause the sealant to be squeezed out completely. If you remove the sender screws, you should use a new gasket when reassembling. If the flange on the tank is smooth and even and the underside of the sender is also smooth and clean, you don't need sealant.
If one or more screws can not be tightened dues to the screw hole stripping, you have to address that first. Uneven tightening of the screws can cause leaks
I also agree that you need to find out how water gets into that area. Just to check; are you sure that is where water is getting into the tank as opposed to the fil and vent l fittings.
 
seasick said:
Over tightening the sender screws can distort the flange and cause leaks. This especially true if you use a gasket sealant and overtighten. That can cause the sealant to be squeezed out completely. If you remove the sender screws, you should use a new gasket when reassembling. If the flange on the tank is smooth and even and the underside of the sender is also smooth and clean, you don't need sealant.
If one or more screws can not be tightened dues to the screw hole stripping, you have to address that first. Uneven tightening of the screws can cause leaks
I also agree that you need to find out how water gets into that area. Just to check; are you sure that is where water is getting into the tank as opposed to the fil and vent l fittings.
Click to expand...
thanks all for the good advice - much appreciated
I just was down at the boat this morning to take another look the sender and possibly remove it but the seal "looks" excellent - gasket tight all round and in good condition
The only other opening is the fill which incorporates the vent as well - there is a new o ring installed in the cap
I suppose if the threads are good on the tank removing it once again and putting a new gasket could not hurt - I think I will try that before any more radical solutions
A mechanic friend said I should pressure test the tank once and for all - but I would need a creative way to seal the fill/vent opening
 
I have seen a poly tank on a pontoon that had a depression in the top that pools water. I did not see any spots that looked like they leaked but apparently they did. The shop that 'fixed' the leak applies some sort of coating that filled in the depression. I wish I knew what they used.
 
seasick said:
I wish I knew what they used.
Click to expand...
Depending on size of the depression, i would use Sika or 5200 to fill it.
If the tank is properly degreased PU structural caulk/glue will adhere to the plastic and can be smooth out if needed.
Thats the first material what comes in my mind as it's flexible, the second one is JB Weld but it may become loose by tank flex.
Chris
 
Butyl rubber tape will offer a better seal than a rubber gasket... and/or you could use the BRT in addition to the rubber gasket.

Gluing PU... it's been my understanding that only way to get a solid bond is to first heat treat the PU to eliminate it's inherent "slipperiness"... which involves using a torch... which obviously that is NOT an option here.

Have things changed regarding gluing PU?
 
I have Butyl rubber strips to try to make the pie plate ring base water tight. MY RV Trailer has all sides sealed with Butyl tape and it works great.

PU caulks or structural bondings can adhere to plastics, but thru a kind of suction cup behaviour.
If size is big enough even Starboard can be bonded using 5200 or Sika 292i, one good example is TransomSaver what is only glued to transom.
Some plastics as PE and PPE should be flamed as you wrote and obviously not a good idea on a fuel tank, but it will adhere also without, just less strong and should be enough to hold a filler to avoid poodles.
Roughening the surface wit sandpaper will help also a bit.
There are primers for Sika 292i what help with bonding strength, the table is to find here
Chris
 
Last edited:
Thanks for the extra info, Chris.

A poly tank will often expand and contract as fuel is put in. do you think 5200/etc will still work with that expansion/contraction? I know they are slightly flexible - just not sure if they are felixbile enough?
 
DennisG01 said:
Thanks for the extra info, Chris.

A poly tank will often expand and contract as fuel is put in. do you think 5200/etc will still work with that expansion/contraction? I know they are slightly flexible - just not sure if they are felixbile enough?
Click to expand...
I like the butyl tape idea - I have have had good luck with that in other applications - I will report results
 
I am reading reviews of butyl tape for plastic tank repairs and it isn't clear if the tape is compatible with solvents and/or gasoline with gasoline being the key word.
I have no experience with gasoline applications using butyl products so if you have any references, please post
 
I meant to add this above...

But... if the sender is torq'd down (by feel, I don't necessarily mean with a torque wrench) evenly, it should seal easily/properly even if the tank is wet. There are lot's of poly tanks where the sender is s exposed to the elements 100% of the time - and those tanks don't suffer water intrusion.
 
DennisG01 said:
Thanks for the extra info, Chris.

A poly tank will often expand and contract as fuel is put in. do you think 5200/etc will still work with that expansion/contraction? I know they are slightly flexible - just not sure if they are felixbile enough?
Click to expand...
I would try it, if it comes off then it will not work, but then i would not know what else to use to fill the depression.
As i wrote, we repaired a black pre 2006 Moeller fuel tank with a bigger (aprox double size of a hand) patch of JB Weld and it held for many years.
Just do some tests if you have some pieces of old poly tank (or other plastics) around, the key for it is size, 5200 will not work on a half inch wide plastic strip but on over 3x3 inch plates and if you test then test also non treated, flamed and roughened surface.

Will butyl rubber not be dissoved by gasoline if used as fuel tank sender sealant?
Or applying it above fuel tank and sender to make a watertight seal similar to a caulk, that should eliminate any leak problem.
Using 4200 or a similar product would work also, but butyl rubber should be more simple to remove if needed.
However, both may collect water/humidity between tank and sealant what will lead to corrosion on the aluminum.
I used successful gasoline resistant sealant for cylinder heads or oil pans between tank and rubber gasket, but only on older aluminum tanks with pitted area where the seal sit. And exclusively for the reason that a rubber seal would not seal enough and the sealant fills the pits, but thats a bandaid solution for a "soon" to replace fuel tank

DennisG01 said:
I meant to add this above...

But... if the sender is torq'd down (by feel, I don't necessarily mean with a torque wrench) evenly, it should seal easily/properly even if the tank is wet. There are lot's of poly tanks where the sender is s exposed to the elements 100% of the time - and those tanks don't suffer water intrusion.
Click to expand...
Yep!
When water seeps in then fuel would seep out if tank is full. As i wrote, even aluminum tanks may collect water around fuel sender and they don't leak if rubber/cork gasket is compressed correctly. The problem with poly tanks is that people are scared to strip the tread and not applying the correct torque what may lead to leak.
Knowing the correct torque setting and using a verified torque wrench is very helpful for installing fuel senders on poly tanks.

Chris
 
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