Blue Stain | fuel leak | Can it be patched or is this a full reseal?

[Teddsgotwings]

Hey there all,

I just picked up a 1978 m20j and while cleaning today I noticed a blue stain. I know it’s a fuel leak but I’m curious how immediate of a fix this needs to be and how big of fix. Can it be patched? Is there a way I can inspect it while there is fuel in the wing? Or is this a full reseal? Can I fly/build some hours for a bit or is this an immediate fix? It’s about 1.5” in diameter. Photo below. I’m in SoCal so if this is a full reseal I’d be curious if anyone has a good recommendation as to who can do it. Thanks all! 

Edited January 31, 2021 by Teddsgotwings

[hammdo]

Looks like a screw - I had the same leak:

Easy fix using permatex #3 aviation gasket maker...

Get the tank low, put the plane uphill (so any fuel left is at the back of the wing), then clean and seal the threads (I’d do the 3 screws in that area). Let it sit for a day, fill and fly it (clean the area before sealing ;o)

-Don

[N201MKTurbo]

That’s just a cover plate leak, easy money.

They are a PITA, but you have to do them for any leak, In this case there is no other leak to fix.

You can tell by the scrapes on that panel that it has been off a time or two. I would just take the screw out, put some Permatex on it and screw it back in.

[Teddsgotwings]

46 minutes ago, N201MKTurbo said:

That’s just a cover plate leak, easy money.

They are a PITA, but you have to do them for any leak, In this case there is no other leak to fix.

You can tell by the scrapes on that panel that it has been off a time or two. I would just take the screw out, put some Permatex on it and screw it back in.

Do I need to drain any fuel before removing the screw(s)? I’ve got about 20 gallons in there. 

[jaylw314]

I'm not so sure that's just the one screw.  You can sort of see a shadow of a larger fuel stain that's 3-4" across, and both the current and old one stretch forwards (and up) along the edge of the access panel.

My guess is a leaky panel, which is still better than resealing the whole tank.

FWIW, the maintenance manual actually categorizes a 1.5" stain as a "seep"

[N201MKTurbo]

You will get a better result if it is dry. 20 gal is a lot, go fly somewhere and have fun with your plane. The easiest way to get the last bit out is to put a bucket under the sump drain and unscrew it. The bucket should be metal and grounded to the plane.  You should have a helper or two buckets unless you are sure you won’t overflow the bucket. You can stop the flow by putting your finger over the hole. You should do this outside. Pour the gas into the other tank. A big metal funnel is helpful although you can pour it in without it if you are slow and careful. Only fill the buckets half full, they are easier to pour that way.

The bottom of the nutplates the screw goes into has a plastic cap. If you put too much sealant in it will push the cap off. That’s probably why that screw is leaking now. Use a new screw, just barely get it started then generously coat the underside of the head and threads with sealant, screw in the screw and clean up with alcohol. 

Edited January 31, 2021 by N201MKTurbo

[carusoam]

Welcome aboard Ted...

Good to see you got wings...  the right wings.

resealing a screw is as easy as it gets...

Challenge is... you need to take the screw out and clean the area to get a good seal...

empty the tank down below where the screw is... or it will empty itself all over the screw driver you are using... (no electric screw drivers for this exercise)

Being new to you... expect that there is a maintenance manual with all the good procedures to help...

Don’t be afraid to find a good Mooney mechanic to help with the easy stuff...  you will want to know him when the hard stuff comes around....

Search around here for Permatex... the right version...

Tank sealants come in two versions... one for inspection panels...

Sealant remover may be helpful...

You have come upon the most simple of fuel leaks... a great way to get started...

PP thoughts only, not a mechanic...

Best regards,

-a-

[carusoam]

What did the pre-purchase inspection say about the fuel leak(s)?

is that a different one near the gear door?

the bright blue... is a fresh deposit...  looks like there has been some older stains semi-cleaned away...

-a-

[PT20J]

5 hours ago, N201MKTurbo said:

The bottom of the nutplates the screw goes into has a plastic cap. If you put too much sealant in it will push the cap off. That’s probably why that screw is leaking now. Use a new screw, just barely get it started then generously coat the underside of the head and threads with sealant, screw in the screw and clean up with alcohol. 

Good idea. Also, never assume that the screw you remove is the correct one. Hardware gets changed a lot over the years. Putting in screws that are too long is a fairly common problem. So, best to look it up in the IPC.

Skip

[bradp]

I could not get the permatex to set up using the wet tank method in don maxwell.  I got it to set up dry but it lasted about 3 months and started leaking again if the plastic ends of the nut plate backing are cracked, it can be worsened by over tightening the screw and pushing permatex up through it.  We eventually took the plate off, I cleaned it for maybe 3 hrs (seriously) and resealed using Chemseal.  Make sure you are using the right Chemseal for access doors not the tank sealer (I don’t recall the part numbers)  - else whomever tries to remove that panel next will hate you forever. 
 

Do what m20k says re fuel safety - make sure that your receptacles are adequately grounded and of the right material.  You don’t want to end up like that drummer in spinal tap. 

[ZuluZulu]

Howdy, neighbor! @Teddsgotwings

[Will.iam]

On 1/30/2021 at 9:54 PM, hammdo said:

 

 

 

 

On 1/30/2021 at 9:54 PM, hammdo said:

Looks like a screw - I had the same leak:

Easy fix using permatex #3 aviation gasket maker...

Get the tank low, put the plane uphill (so any fuel left is at the back of the wing), then clean and seal the threads (I’d do the 3 screws in that area). Let it sit for a day, fill and fly it (clean the area before sealing ;o)

-Don

Ok there are like five different permatex #3 aviation gasket maker versions on amazon which one is correct or does it matter?

[Will.iam]

Just now, Will.iam said:

 

Ok there are like five different permatex #3 aviation gasket maker versions on amazon which one is correct or does it matter?

 

[EricJ]

1 hour ago, Will.iam said:

 

Either of the bottom two, PN 80019.   PNs 80018 and 80017 are the same stuff in smaller and bigger bottles, respectively.

Edited February 13, 2021 by EricJ

[Teddsgotwings]

On 2/10/2021 at 10:49 AM, ZuluZulu said:

Howdy, neighbor! @Teddsgotwings

 

Well hello! Just seeing this now. Where are you based out of? Im at KSMO and would love to learn some good flights around SoCal as Im pretty new to the skies here. 

-Tedd

[ZuluZulu]

12 minutes ago, Teddsgotwings said:

 

Well hello! Just seeing this now. Where are you based out of? Im at KSMO and would love to learn some good flights around SoCal as Im pretty new to the skies here. 

-Tedd

I will PM you.

[drapo]

Reviving this link to get some more details. Annual is coming and there are some blue seeping marks around the fuel access panel on the bottom of the wing. Mechanic says he'll be able to repair it, as he's done it before on other Mooneys but I'm not sure which product should be used.

The SB talks about PRC1321 (Now PRC1428) being the solution but some are talking about CS3330B. Is the only difference the company that makes the stuff (Permatex vs FlameMaster) or should I stick with what the SB says?

[PT20J]

You can ask the factory for the current recommendation: technicalsupport@mooney.com. They've been pretty good at getting back to me lately.

[JWJR]

Looks like just a screw. The permatex usually works however it really never sets up. I just back the screw out a bit and brush on the permatex. The fuel won’t pour out… more like a seep/drip. (Wear rubber gloves)Use the brush and coat the screw and tighten until snug. Do not over tighten. It could also be the seem around the inspection plate. If that is the cause it’s a little more involved as you will need to drain the tank. Remove the inspection plate and reseal however still not more than a few hours of labor and the cost of sealant. Full tank resealing is 5k per side. Most patch leaks as they appear until they appear too frequently and inspection indicates sealant is in poor condition. Some recommend to keep the tanks full during the warm months of the year to prevent the sealant from becoming dry and brittle. Some avgas on a rag will remove the blue seep stain. (Ironic huh)
You mentioned the plane is a recent purchase. I know it’s been dry out west however it will eventually rain so ensure your gas cap o-rings are new - not cracking and in good condition as the accident reports have found that cracks in the O-rings allowed rain water in the tanks with fatal outcome. Especially important for planes tied down outside. The O-rings are inexpensive and simple to change. Enjoy your new to you plane!


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[ArtVandelay]

Looks like just a screw. The permatex usually works however it really never sets up. I just back the screw out a bit and brush on the permatex.

Permatex is a brand name…which sealant ?

[JWJR]

I’ve used the Permatex 80019 number 3 for a couple of screws. The same permatex referenced earlier in the thread. Don Maxwell had a link on his website about fuel leaks that went into great detail around leaks and repair procedures. I’m not sure if the article/link is still on his website however. If someone has the article or link please share.


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[laytonl]

I’ve used CS3330B on screws with good success.  Lee

[hammdo]

5 hours ago, JWJR said:

Looks like just a screw. The permatex usually works however it really never sets up. I just back the screw out a bit and brush on the permatex. The fuel won’t pour out… more like a seep/drip. (Wear rubber gloves)Use the brush and coat the screw and tighten until snug. Do not over tighten. It could also be the seem around the inspection plate. If that is the cause it’s a little more involved as you will need to drain the tank. Remove the inspection plate and reseal however still not more than a few hours of labor and the cost of sealant. Full tank resealing is 5k per side. Most patch leaks as they appear until they appear too frequently and inspection indicates sealant is in poor condition. Some recommend to keep the tanks full during the warm months of the year to prevent the sealant from becoming dry and brittle. Some avgas on a rag will remove the blue seep stain. (Ironic huh)
You mentioned the plane is a recent purchase. I know it’s been dry out west however it will eventually rain so ensure your gas cap o-rings are new - not cracking and in good condition as the accident reports have found that cracks in the O-rings allowed rain water in the tanks with fatal outcome. Especially important for planes tied down outside. The O-rings are inexpensive and simple to change. Enjoy your new to you plane!


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https://web.archive.org/web/20200619034846/http://donmaxwell.com/fuel-tank-repairs-how-we-fix-them/
 

-Don