leak at sender on top of fuel tank

gkny

Member
345
26
I ended up overfilling the tank with diesel and got some leaking where the sender attaches to the top of the tank.  The tank is stainless steel but fairly thin.  I pressed on the top and some fuel leaked from under the sender.  The screw in that vicinity is stripped.  I wondered what the best approach to fixing this is.  One option would be to use something like a rivnut.  I am not sure of the flange would sit too proud for the gasket material to seal properly.  Another option would be to try to go with a slightly larger screw and tap new threads.  Another possibility would be to try to clean up the stainless and epoxy a nut to the inside of the tank wall.  It would have to hold well enough to resist spinning when tightening the screw.  Any suggestions or past experiences would be appreciated. 

fuel tank.jpg

 

El Borracho

Sam’s friend
6,436
2,452
Pacific Rim
A threaded backing ring is the best permanent solution. A bit painful to fabricate with home tools, though, given the difficulty of cutting big round holes in thick plate. The ring can be held in place by some small flathead screws under the gasket or goop sealed pop rivets outside the fitting.

Or rotate the fitting and drill fresh holes. Use the best gasket goop NAPA sells. I like a red silicone rubber PERMATEX goop I got somewhere. 

 

IStream

Super Anarchist
10,784
2,970
Or rotate the fitting and drill fresh holes. Use the best gasket goop NAPA sells. I like a red silicone rubber PERMATEX goop I got somewhere. 
This. The old holes will be sealed by the gasket. Fast, easy, solid fix.

 

andykane

Member
438
202
Victoria, BC
Just be extra careful not to drop any scraped off bits of the old gasket into the tank. I can say from experience that a scrap of permatex can make a vacuum tight seal on the bottom of your fuel pickup. Interestingly this only happens when a) when you're about to enter the narrowest point in a channel and a bunch of Orcas suddenly surface to make things interesting or b) visibility is a couple boat lengths in thick fog and you're bouncing around in oily west coast swells.

 

Quickstep192

Anarchist
741
133
Chesapeake
12 hours ago, El Borracho said:Use the best gasket goop NAPA sells. I like a red silicone rubber PERMATEX goop I got somewhere. 
Do you prefer the red Permatex to the gasket that comes with the sending unit?
 

I’m getting ready to replace my sending unit and wondering if the permatex is superior to the rubber gasket that comes with the sender. My tank is polypropylene or polyethylene.

I don’t have any stripped threads (yet) 

 

longy

Overlord of Anarchy
6,501
1,002
San Diego
Examine the sensor - does it have a float on an arm? Then the alignment of the float arm in the tank is important to it's performance. It needs to be unhindered in it's movements, & ideally mounted fore/aft (less sloshing). If the float just moves vertically, no alignment issues.

 

El Borracho

Sam’s friend
6,436
2,452
Pacific Rim
Do you prefer the red Permatex to the gasket that comes with the sending unit?
 

I’m getting ready to replace my sending unit and wondering if the permatex is superior to the rubber gasket that comes with the sender. My tank is polypropylene or polyethylene.

I don’t have any stripped threads (yet) 
Hard to know. Some rubber gaskets seem too hard to make a sweet seal given the fear of stripped threads. With the rubber I’d use a non-hardening gasket goo.

Sometimes the aluminum tanks are not very flat because of tortured cutting of the hole. The silicone can accommodate that. 

 

ROADKILL666

Super Anarchist
2,383
534
FREAKVILLE, FL
A threaded backing ring is the best permanent solution. A bit painful to fabricate with home tools, though, given the difficulty of cutting big round holes in thick plate. The ring can be held in place by some small flathead screws under the gasket or goop sealed pop rivets outside the fitting.

Or rotate the fitting and drill fresh holes. Use the best gasket goop NAPA sells. I like a red silicone rubber PERMATEX goop I got somewhere. 
What he said. It’s a bitch but it works. 

 

Quickstep192

Anarchist
741
133
Chesapeake
A threaded backing ring is the best permanent solution. A bit painful to fabricate with home tools, though, given the difficulty of cutting big round holes in thick plate. The ring can be held in place by some small flathead screws under the gasket or goop sealed pop rivets outside the fitting.
Such a great solution that you might think the tank manufacturer would do it! It would probably take two minutes to do while the tank was being fab’d…

 

gkny

Member
345
26
When I see the amount of flex in the tank wall it seems like maintaining a good seal is challenge without a backing plate of some kind.  On the other hand, the tank is 30 years old so maybe not as much of a problem as it looks like.

 

El Borracho

Sam’s friend
6,436
2,452
Pacific Rim
I should add the backing ring needs to be held in place only enough to get the mounting screws started. One pop rivet or little screw is enough. Two is deluxe. 

 

Startracker

Member
390
103
Van Isl.
A threaded backing ring is the best permanent solution. A bit painful to fabricate with home tools, though, given the difficulty of cutting big round holes in thick plate. The ring can be held in place by some small flathead screws under the gasket or goop sealed pop rivets outside the fitting.

Or rotate the fitting and drill fresh holes. Use the best gasket goop NAPA sells. I like a red silicone rubber PERMATEX goop I got somewhere. 
This.  I use a bit of wide sticky tape, stick it through the hole, pull it up into place with a finger.  Scrape and sand with a shop vac running right next to it, one half at a time.  Sanding for gasket is key IMO.  Obviously no vac on gasoline tanks unless you like BBQ. 

Set it back in on the correct holes, rotate until roughly in the middle of holes(it won't be perfect because of the spacing) but usuallly this is close enough that the arm won't jam up on the side of the tank. 

For gasket, a sheet gasket and a THIN layer of goop.  If too lazy for gasket material or the surface is good enough, Permatex Ultra black(thicker more paste like, won't end up dribbling into the fuel, red is OK if you can't find black but the black being stiffer will build a better gasket IMO).  Alternative but not recommended: clean the hole up, hit it with a countersink bit to give a bit of a shoulder, fill with aluminium filled epoxy putty(JB weld) after solvent wipe.  Re-drill hole, reinstall. 

 
Seems like a perfect spot for rivnuts.  Make sure you take your time drill out to the right size hole and get a good set.  Probably wouldn't even worry about using steal.  I would make a new rubber gasket with the fastener holes the size of rivnuts. Put a thin amount of Permatex RVT on the tank top and on one side of the gasket.  I would have to look but I believe red, black and blue are all petroleum resident. So any would work.  I usually try to keep a couple small tubes of red as it covers all the bases.  You should let it sit and almost skin over before putting together. Put all the pieces together then put a small amount on the screws and tighten up. Cleanup with dry cotton rag no solvent.  If you wanted to get crazy you could use oversized pan head screws with a seal washer under but I would use a Allen machine screw, looks like M5 or M6 for that.

 
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