repair fuel sender leak

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PatSea

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Hope everyone is having a fun filled Memorial Day. I recently had the fuel sender gage replaced on the top of my 80 gallon aluminum fuel tank. It included a new rubber gasket. Now I have a thin film of gasoline migrating from the top of the tank around the fuel sender gage after I fill the tank. I don't know if it's coming from under the gasket or if it's wicking up the mounting screw threads or both. As I was inspecting the area I noticed that one of the sender mounting screws would not tighten very much. The threads are stripped. So I have a strong hunch that this is the cause of the leakage. I'm trying to determine the best way to repair this.
I have searched this forum and read many threads about this topic and learned a lot. I think I am going to repair it by using a larger machine screw by drilling and tapping for the next larger size screw. (unless someone on here talks me out of it). When I get back to the boat I'll have to check to be sure I have enough wall thickness to accommodate a larger screw.

I'm trying to get all my ducks in a row so I have the correct materials and tools when I get to the boat which is three hours away. So, a few questions:

1. I'm assuming the threaded holes in the top of the tank are through holes, is that correct? They're not blind holes?

2. What is the standard size of the screws used on these sender units? 10-24 or 10-32?

3. Assuming it's a #10 machine screw now, what next size larger machine screw should I use?

4. I've read conflicting views on whether to apply a sealant between the new gasket and the top of the tank. The one sealant that seems to get high marks as gasoline insoluble is Permatex aero #2. Should I use that or no sealer at all.

5. I understand a new gasket kit includes the gasket, machine screws and small rubber gaskets that fit around the mounting screws to prevent gas leaking around the threads.

Any other suggestions? Thanks for your help.
 
If you must drill use a hand drill. NOTHING TO PRODUCE A SPARK
I use PermaTex Aviation sealant.
Can use the next size standard or go next size metric
 
There are "C" shaped backing plates that are available. The notch allows installation through the opening. I assume you hold the plate in place with some string until you get a couple screws started. That solution may fit your needs and requires no drilling.
 
I would remove the sender , remotely drill slightly larger the one hole over the stripped tank hole , use same-type, next-larger dia. SS screw with SS and rubber flat washer (and/or maybe a tiny nitrile O-ring as add'l seal as some use) and reinstall with a new nitrile/buna-n gasket without enlarging the tank hole or using sealer unless the tank surface is badly corroded and can't be cleaned up to relatively smooth mating surface.

But here are the repair inside-the-tank split rings to which Shake n Bake refers (10-32 sender fasteners threaded holes: may need longer than originals ) :
http://www.tanksinc.com/index.cfm/p...ct_id=100/category_id=62/mode=prod/prd100.htm

They work great to hold tight, but may be difficult to hold in place for the sender mounting or subsequent removal. If you use these, it may be wise to note that on the tank.
 
Thanks for the ideas! And yes I will have all batteries disconnected and shore power disconnected when I do this. No power tools, I might be able to use a small hand drill if I need to drill the tank holes slightly larger for a next larger screw.
I've ordered one of the C shaped backing plates as Shake N Bake mentioned. I'm just not sure how to hold the plate in place inside the tank as I start the screws. As suggested may be able to thread string through a hole to hold the plate in place while I start the first screw. If I can get one screw started I should be able to get the rest of them aligned and insert the screws.
Thanks. guys!
 
Epoxy the plate in place using the screws without the sender. After the epoxy sets, you should have no problem. Just don't epoxy the screws to the plate.
 
Epoxy is a great idea. I hadn't thought of that. It will hold the backing plate in place if you have to remove the sender in the future. Thumbs up!
 
What epoxy would you use? Would be good if it was insoluble in gasoline so it stays in place if I ever have to remove the sender unit again. I will put a tag on the sender describing the repair and the use of the internal plate. Thanks again for all your help!
 
When mine were replaced a few years ago I also had the weeping you speak of. Used the red gasket sealer, gas would not affect it, and to this day no problems. If and when I have to remove the sender again it's just a simple putty knife to remove and a little sand paper to clean and do again.
 
Well I repaired my leaking fuel sender and the job actually turned out to be easier than I expected, mainly because none of the sender mounting screw holes were stripped as I had originally thought.
I took the sender unit and gasket off the top of the tank, ran 10-32 tap through them to clean them, and ran the 10-32 screw in each one and determined that the threads in the tank were not stripped as I first thought.
The top mounting surface of the tank was rough from crud so I used crocus cloth to sand the surface clean and smooth, being careful not to get any in the tank. I applied a thin layer of Permatex aviation gasket sealer to the top of the tank and to the new rubber gasket. I reassembled the sender assembly with the original screws.
The sender unit no longer leaks even after I filled the tank. I will continue to monitor the sender but I am convinced that this is a good, permanent repair.
A couple of interesting notes. The screws and washers that came with the new Moeller gasket/screw kit would not fit on my sender unit. The diameter of the screw head and the washers were too large.
The original screws had small nylon bushings under the head of the screw which were apparently used to seal the screw threads. Since the new washers with rubber seals did not fit I reused the nylon bushings.
 
Good work. Nylon washers or bushings there are often used in conjunction with tiny nitrile o-rings. Whatever works is good!
 
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