How can I stop diesel leak at sender unit?

[hlev00]

I have a plastic diesel fuel tank that has developed a leak at the sender. The problem seems to be caused by one of the screws that has stripped the hole in the tank and won't bite. Other screws are secure. I saw some suggestions of creating a backing plate but I'm not in a position to do that at this point so am looking for an interim solution.

I am thinking of
1. Using a small amount of 4200 to seal the screw hole.
2. Apply 4200 around the sender to seal the leak between the tank and the sender plate.

Is 4200 the right stuff to use? Will it seal from the outside? I'm concerned about the 4200 coming off the screw and ending up in my fuel line, though hopefully the primary filter would pick it up.

Do you have any other alternative approaches?

Thanks,
Harry

[model 10]

Use a tooth pick or something small and spread the sealant evenly inside the threaded hole. This should keep any excess from falling off the end of the screw inside. With a plastic tank you choice of sealant is a bit more tricky. I think you should make sure it's a polysulfide of some sort.
One trick is to make a small seal from a washer and an O ring. It's called a Lock O seal. You can make your own by using a flat washer that is bigger than the screw and put a small O ring in the middle. When you tighten up, the oversize washer keeps the O ring from squishing out. The sealant should keep the screw tight and the seal will keep it from leaking.

[exMaggieDrum]

Good luck with any sealant if diesel is already present. And I don't think 4200 will work on your plastic tank material. Do a search on repairs to poly tanks. There was just a long thread on that. The diesel just complicates things.

[cabo_sailor]

Can't you just replace the stripped out screw with a slightly larger one?


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[Lepke]

Most auto supply stores have rethreading kits that include a tap, drill and a bushing that has threads that are the same thread as the screw inside and threads to match the tap on the outside. You drill the hole oversize and then tap and install the threaded insert. Use loctite or similar to adhere insert to tank. Diesel shouldn't be a problem unless tank is full. Use acetone to clean threads of diesel if necessary. Insert is usually stainless and lasts the life of the tank.

[Cheechako]

Originally Posted by cabo_sailor

Can't you just replace the stripped out screw with a slightly larger one?


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This. Run the next size tap drill thru. Tap the hole, put a screw with the seal on the screw head in from the inside out. You now have a stud sticking up thru the tank top. Put a nut on the stud on top of your sender.

or if the old screw bites at all, just put it in from the inside of the tank out as a stud.

[cabo_sailor]

Originally Posted by Cheechako

This. Run the next size tap drill thru. Tap the hole, put a screw with the seal on the screw head in from the inside out. You now have a stud sticking up thru the tank top. Put a nut on the stud on top of your sender.

or if the old screw bites at all, just put it in from the inside of the tank out as a stud.

If you're installing a bolt, why do you need to tap the hole. I can also see the possibility that due to baffles or some such access to the tank interior may be problematic.

Your choice or mine might work. Frankly I like yours better. Just a question of access I guess. I don't know where his sender is located.

Rich


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[Cheechako]

Originally Posted by cabo_sailor

If you're installing a bolt, why do you need to tap the hole. I can also see the possibility that due to baffles or some such access to the tank interior may be problematic.

Your choice or mine might work. Frankly I like yours better. Just a question of access I guess. I don't know where his sender is located.

Rich


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So it doesn't fall into the tank when you take the nut off! Hopefully there is an access plate, but could be done thru the sender hole too.
I made a tank once and did it this way on the access cover, if the bolt threads strip it's replaceable. If the hole strips on the other style of tank... more trouble.

[hlev00]

Thanks for all the suggestions. I am trying Cabo's suggestion of the larger self tapping screw. I might have needed to drill out the top metal ring as i'm not sure if the screw is drawing the tank up to the sender unit. I don't have an inspection port but might still be able to try Cheechako's stud idea. We had lots of rolling and bouncing beating yesterday. I will check the tank later today to see how the screw worked.

Thanks all!



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[ex-12m-guy]

For a sealant on fuel system items, try Permatex no 2. available at auto parts stores.

Permatex is resistant to gasoline and diesel. Many other "marine" grade sealants are not.

[sailon46]

Careful using sealants in diesel tank. I chased when in Grenada a couple of years ago a ghost of lack of diesel flow to my genie It ended up been a sealant plug in the sending unit. Easy to fix expensive in money and time to find it. Find a larger screw no sealants

[Jim Cate]

Originally Posted by ex-12m-guy

For a sealant on fuel system items, try Permatex no 2. available at auto parts stores.

Permatex is resistant to gasoline and diesel. Many other "marine" grade sealants are not.

Agreed! Good old Permatex sealed just such a leak for us at sea in nasty conditions some years ago... simply slathered on from the outside.

Sometimes the old stuff is the good stuff!

Jim

[TKDSailor]

Originally Posted by Lepke

Most auto supply stores have rethreading kits that include a tap, drill and a bushing that has threads that are the same thread as the screw inside and threads to match the tap on the outside. You drill the hole oversize and then tap and install the threaded insert. Use loctite or similar to adhere insert to tank. Diesel shouldn't be a problem unless tank is full. Use acetone to clean threads of diesel if necessary. Insert is usually stainless and lasts the life of the tank.

You can search for either "Threaded Inserts" or Helicoils for the product...

[hlev00]

Originally Posted by TKDSailor

You can search for either "Threaded Inserts" or Helicoils for the product...

I have a plastic tank. I wouldn't have thought the thread inserts would be useful.


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[sanibel sailor]

Threaded inserts are designed for metal, doubt it would work on plastic. A riv-nut works on plastic, but would stick up and prohibit a good seal. Permatex #2 is a godsend. The only stuff it does not work well for is alcohol. Probably not much help if the screw does not bite however. Goop outside the leak is rarely successful. If using a bigger screw (easiest approach), you will need to drill the plate on the sender a bit oversize so the screw will compress the gasket. Do not drill down into the tank with that bit. Also, if you are removing the sender, make sure you know which is the correct hole. The pattern is an SAE standard and only lines up one way. Good news is that you can pick up a new gasket at any auto part store.