Old, soft proseal...

Hi Folks!

I had some fuel weeping around the fuel sender on the right wing tank in my 25 year old RV-4, so I dropped the tank to inspect it and find the source of the leak. Imagine my surprise when I was able to scrape off the proseal around the sender and inspection plate with a fingernail! The rest of the accessible proseal on the tank is hard as is the other wing tank (which I previously removed a couple of years ago to replace the sender and add AOA plumbing forward of the spar).

I suspect a bad batch of sealant was used for the sender and inspection plate when the airplane was first built (or perhaps an non-hardening formulation). After a quarter century and couple of thousand hours, gas simply started to weep from some of the screws...

I will clean up the old sealant and reseal the plate and replace the old style Stewart Warner sender; but I'm curious if anyone has run into something similar and there are any lessons learned that might apply!

Happy New Year,

Vac

Happy New Year !!

Dubbed "reversion" and oddly seems to happen with damp proseal resulting from weeps. It is not unusual, and is frequently claimed to be a result of poorly mixed product. I contacted the 3M lab engineer for polysulfone products and she did some research on their documents and could not find any history of this. With the few cases known, and they were not using 3M product, the investigation ended there.

A local friend in a nearby hangar just had the same "failure" due to a persistent small weep. RV8 ~8 yrs.

DanH has the most complete information, but fits into your description.

Hi Vac,
I had the same thing happen on my right tank. I took the tank off, cleaned up the area, and was going to replace the sender too. The new Stewart-Warner sender from Vans’ had a different bolt hole pattern, so I reused the old sender. I also used the 3M brand “Proseal” vs what Vans sells, as that brand is the one with issues. I called that company, and after speaking with their “engineer”, I threw it in the trash and went with 3M. No leaks. I also wound up doing the access plate on the same tank, as the sealant was reverting there too. The other tank, done at the same time, same batch, has no issues. Go figure.

Michael Henning said:

I also used the 3M brand ?Proseal? vs what Vans sells, as that brand is the one with issues.

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I bit of research will show that the softened sealant issue from extended exposure to leaking fuel has happened with numerous brands of sealant.

Additionally, lack of a leak on the other side doesn't mean the same thing wont occur there as well if a leak ever does start.

The leak doesn't start because of softening sealant.... the sealant softens and degrades because of extended exposure to a leak.

A lot of info available here in the forums with a bit of searching.... it has been discussed extensively in the past.

Thank You!

All,

Thanks for the quick replies. Key words that worked well for search were "soft proseal."

Another lesson learned thanks to the awesome group resource that VAF is!

Cheers,

Vac

My theory is that it's the blue dye in the fuel. The pro seal is fine with exposure to 100ll, but when the gas evaporates and leaves only the dye, it softens the pro seal. Has anybody that uses only auto fuel has the softening problem.

Bob burns
Rv-4 n82rb

n82rb said:

My theory is that it's the blue dye in the fuel. The pro seal is fine with exposure to 100ll, but when the gas evaporates and leaves only the dye, it softens the pro seal. Has anybody that uses only auto fuel has the softening problem.

Bob burns
Rv-4 n82rb

Click to expand...

Yes. I only use LL when forced to when I travel; E-free premium mogas at home. I've seen softened sealant on my 1991 era tanks.

DanH has linked to research papers showing degradation from gasolines; IIRC, the issue was related to peroxides.

Charlie
(not a chemist; no hotel stays lately)