diesel tank leaking at exit fitting, plastic tank, brass fitting

[terex herder]

I have a plastic diesel tank with about 250 gallon capacity on a combine. There is a molded brass exit fitting that is weeping between the brass and plastic. I have room to install a steel plate larger than the brass fitting and tighten it against the plastic. The brass part is hex shaped, about 1 1/2" across flats. I have plenty of room for a 2 1/2 diameter piece to seal around the brass. My go-to would be an o-ring to seal against the plastic of the tank. I am wondering if there is a conformal gasket material that would be a better choice than an o-ring.

 

[skyking1]

I think hylomar will seal diesel.
That with a silk thread embedded in it is how we seal the two case halves of an aircraft engine. It's really good stuff.

 

[Coaldust]

I’m all ears. I’ve tried fixing these things in many different ways. Lube and fuel service, with no luck. But, if anyone can figure it out, it will be an ag mechanic/farmer.

 

[Welder Dave]

Petro tape from Jet Lube and/or a thread sealant paste. Gasoila has a diesel specific thread sealant and Permatex and Loctite also have suitable sealants for diesel. Have heard regular Gasoila is the best for gasoline so their diesel sealant is likely very good as well. If it needs an o-ring type seal a flat rubber type washer might be better than a round profile o-ring.

 

[Welder Dave]

Double post

 

[joe--h]

I had the same problem on my MF fuel tank, new tank was $1200 and guaranteed to do the same thing in a few years. I had a local shop make a steel tank. Lost a few gallons as it didn't have all the odd bumps the original did but it doesn't leak AND it wasn't $1200.

But you might try a bulkhead fitting and get lucky. I think it you keep the tank vented you'd have better luck as it won't pressurize when it gets hot.

Amazon.com : Compression Bulkhead Fittings

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Amazon.com : Compression Bulkhead Fittings

Joe H

And it's not thread sealant that he needs, it's the original bond to the the molded in the brass fitting.

 

[Welder Dave]

Then an epoxy should work if it's fully cleaned.

 

[joe--h]

Actually nothing sticks to that damn plastic, and diesel just keeps seeping out of the joint.

Can't imagine the manufacturers don't know about it but it takes long enough to be way out of warranty so no my problem.

Joe H

 

[Welder Dave]

Could a soldering iron or plastic welder melt the plastic so it seals? It sounds like the weeping diesel is contaminating the plastic. Seems there should be a contact cleaner or chemical that could clean up the diesel.

 

[joe--h]

It's a brass piece that was molded in place when the tank was formed. Eventually the bond between the plastic and brass lets go and it leaks.

It's a stupid design that is unrepairable.

Joe H

 

[Acoals]

It would seem like a bulkhead fitting would be worth a try.

It's hard to think any kind of goop is going to fix that.

 

[Welder Dave]

How thick is the tank? Could a washer that fits around the fitting be screwed into the tank with a rubber washer and/or sealant under it? If it was mine I'd try a couple things first before removing the fitting. I'm so glad I don't have any plastic tanks on my equipment. Have heard some horror stories with them.
I saw this and maybe it's worth contacting them? There's also some fuel tank sealers certified for aircraft that may work.

Polypropylene Gas Tank Repair- It CAN Be Done | Tech-Bond Solutions

When you google polypropylene gas tank repair, google gives you a snippet from itstillruns.com that claims

tbbonding.com

 

[skata]

Can you just clean the area real good and slather some rtv silicone around the brass? I've done that on oil pans with success.

 

[treemuncher]

Compression bulkhead fitting is the way to go. BTDT. Knock out the original piece of crap molded into the plastic tank, drill to size required and install new fitting.

 

[joe--h]

Looking at that site I don't see anything like what TH needs, or I didn't see it. Looks like they patch holes, but that ain't the problem.

Rip the brass piece out and try a big bulkhead fitting or maybe patch ir with that stuff and a smaller fitting.

It's just a pisspoor design with no easy solution except a new tank that will do the same thing again.

Joe H

 

[Welder Dave]

I thought the repair stuff I posted above might stick to the plastic but if you can get a bulkhead fitting in wouldn't rely on a type of glue or sealant. Not sure how hard it would be to get the bulkhead fitting inside the tank though.

 

[joe--h]

The problem is it has to stick to the brss and the plastic. Their web site doesn't mention it or I didn't find it.

Considering the number of tanks out there with this shitty mess of a design I'm thinking IF they could fix that it would be front and center on their site.

Joe H

 

[Welder Dave]

Not sure if manufacturers monitor fuel tank repairs very much. They'd probably rather sell a new tank than admit there was a flaw with their original tank. A little bit similar to the leaking oil pan on my F150 2.7 Eco Boost. I think some 3.5 Eco Boosts also leaked. Known problem and multiple claims under warranty but no coverage out of warranty. It wasn't considered a safety issue so no recall. However it was a recall on the police version F150's with the same engines. Manufacturers aren't very forthcoming admitting they have defective parts. I imagine if diesel was as volatile as gasoline they might be required by law to address the problem.

 

[terex herder]

I made a piece to fit against the bottom of the tank that covered the brass fitting and about 1/2" beyond. I had to trim the flash line on the tank smooth with the brass fitting. I made a piece with external threads to fit on the elbow, and a piece with internal threads I could turn to tighten against the patch.



Per Skyking1 suggestion i used hylomar to seal the patch against the tank. The collar is just to keep the patch from falling off.



24 hours, still dry.

The previous version had a bulkhead fitting. I considered one here, but the fitting is about 5' horizontal and around the corner from the fill riser.

 

[Welder Dave]

That's along the lines of what I was thinking with a washer. The threaded sleeve is great way to hold it tight. I think even a flat neoprene (or diesel resistant) rubber washer could have been cut and used instead of sealant since the threaded sleeve could apply quite a bit of pressure on it.