Rust in Fuel Sump?

[LevelWing]

I've noticed this the last couple times I sumped the fuel during pre-flight. It only occurs on the left tank, and only happens the first or maybe second time I sump it. After that it's clear. The fuel itself is clean and this only appears when you first press it into the valve. The aircraft has spent the last nearly 10 years in the desert southwest and is now in south Florida. I assume it's a little rust around the area of the sump valve, but I'm not completely sure. Does anybody have any better guesses? Pictures attached.

[N201MKTurbo]

It is usually deteriorated tank sealant. About the only steel in the tank and fuel system is the ring the fuel cap goes into.

[LevelWing]

Just now, N201MKTurbo said:

It is usually deteriorated tank sealant. About the only steel in the tank and fuel system is the ring the fuel cap goes into.

Thanks. Is this something to be concerned about?

[N201MKTurbo]

Your plane sat for a long time. I would keep an eye on it and see if it gets flushed out.

It might have been pumped in there when you filled up. 

[ArtVandelay]

Thanks. Is this something to be concerned about?

How long between samples?

[LevelWing]

Just now, N201MKTurbo said:

Your plane sat for a long time. I would keep an eye on it and see if it gets flushed out.

It might have been pumped in there when you filled up. 

Thanks, I'll keep an eye on it then.

Just now, ArtVandelay said:

How long between samples?

I sump it back to back multiple times and after the first or maybe second time I don't see it anymore. I noticed earlier this week and didn't notice anything out of the norm during the flight. I noticed it again today after I fueled up.

[ArtVandelay]

I sump it back to back multiple times and after the first or maybe second time I don't see it anymore. I noticed earlier this week and didn't notice anything out of the norm during the flight. I noticed it again today after I fueled up.

If you are seeing this every time it sits for a week, then I would be worried. I’d have the tank drained and inspected, if sealant is in bad shape have it stripped and resealed.

[LevelWing]

11 minutes ago, ArtVandelay said:

If you are seeing this every time it sits for a week, then I would be worried. I’d have the tank drained and inspected, if sealant is in bad shape have it stripped and resealed.

I'll watch it over the next week or so. I'm hoping @N201MKTurbo is right and that it's a by-product of how long the plane sat, especially going from the desert southwest to the extremely humid southeast.

[N201MKTurbo]

If your tanks are going to leak they are going to leak. there is no preventative measure to take. Repairing a tank that isn't leaking is silly. My old M20F would emit red particles periodically, but the tanks never leaked.  You don't want that stuff in your fuel injection system, but it has 4 screens to get through before it gets there.

[Hank]

5 hours ago, LevelWing said:

I'll watch it over the next week or so. I'm hoping @N201MKTurbo is right and that it's a by-product of how long the plane sat, especially going from the desert southwest to the extremely humid southeast.

At least Wet Wingologists is nearby if you end up needing a strip and reseal . . . .

But do check the filler neck where the gas cap locks in, those are known to rust if not replaced with stainless steel versions.

Edited August 8, 2020 by Hank

[carusoam]

1) is this rust?

2) If yes... it isn’t going to get better on its own... (odd that there is so much in one tank all of a sudden?)

3) If no... let’s figure out what it is.... And where it came from...

4) Mid 60s Mooneys are known for having a rust source at the top of each fuel tank.... (Rich gave a great explanation above)

5) A single pic comparison is all it takes...

6) Swapping in a SS part in place of the mild steel part will end the rust issue...

7) Discussing rust challenges is simple... nobody wants them...

8) Rust particles come in various sizes...

• some fall to the bottom of the tank... before moving towards the sump drain...
• often the sump drain gets stuck open with all the tiny sand like particles in it....
• some Particles float with the fuel to get past the first course screen on the fuel pick-up in the tank...
• When they get this far, they land on top of the fuel separator screen, until they are small enough to get through the screen... Where they sit in a drop of water and oxidize some more...
• At this point you may be catching rust particles as they drain out when you pull the ring....
• Nothing stops these particles from heading towards the fuel delivery system for the engine...
• One more screen to go... closer to the engine.

So... If you have rust particles... identify the source... a non shiny, non smooth, fuel tank neck is one made of mild steel... it rusts and sheds particles...

Solution... replace said neck... with a modern SS one... they don’t rust... so they don’t shed...

Replacing these parts is a bit expensive, and probably needs some sealant to complete...

My 65C’s fuel necks looked fine from the outside... until the hole rusted all the way through from the inside... large amounts of water in the tank made it more than obvious what was happening...

The days before MS were more difficult than the days after MS... 

Post a nice close-up of your fuel neck’s surface... this is the shaped metal part that the fuel cap sits in... if it isn’t shiny and mirror finished... And is more gray with traces of stress marks left over from forming...

Plan on swapping in a new part or two... less cost than resealing the tank by far...

But... don’t do it until you have found that it is rusting... swapping parts just because won’t win any precious CB awards...  pics from inside the tank of the back side of the neck... would be great!

PP thoughts only, not a mechanic...

Best regards,

-a-

[ArtVandelay]

A foreign object could have gotten into the tank, we’re assuming it’s rust. Instead of guessing, either pull an inspection panel, or pull the sender or use a borescope through the fill port and see what’s going on.

The chains some have on their fuel caps....are those stainless?

[carusoam]

Just now, ArtVandelay said:

The chains some have on their fuel caps....are those stainless?

Probably depends on the age of the chains...

I have a new shiny chain... that was added along the way... where the plastic one had failed...
 

I wouldn't expect 60s chains to be so luxurious... to have SS back in the day...

SS requires more technical effort to manufacture into parts.... more available today...

Best regards,

-a-

[Hank]

5 hours ago, carusoam said:

Probably depends on the age of the chains...

I have a new shiny chain... that was added along the way... where the plastic one had failed...
 

I wouldn't expect 60s chains to be so luxurious... to have SS back in the day...

SS requires more technical effort to manufacture into parts.... more available today...

Best regards,

-a-

My 1970 C has no chains on the fuel caps. I thought those were a long body thing, and that they were later removed by AD.

[N201MKTurbo]

The fuel level sensors are steel also.

[ArtVandelay]

The fuel level sensors are steel also.

Of course they need water for rust, and to the level of the fuel sensor that would be a lot of water. I was think fuel cap chain that fell off is now sitting at lowest point of the tank, where a little water sits that’s not being drained.

[LevelWing]

I don't see any rust around the fuel caps, and mine are connected by a plastic tube. I'll check a few more areas the next time I'm at the airport, but at this point I think @N201MKTurbo is probably right with the sealant. 

[David Lloyd]

A couple months ago I had a sump drain start leaking and could not get it to stop.  Looked at the O&N bladder drawing, it specified an F391-18 drain.  Got it from Spruce.  It appeared to be cad plated steel.  Removed the old one and it appeared a little bit of water at the very bottom of the tank, undrainable without removing the drain, had caused a little rust inside the valve where the o-ring sealed. When I bought the plane a year ago, there was water in the left tank.  Every time I flew, there were a few drops of water in the cup from the left tank only.  Finally got the water cleaned out and replaced the little o-ring at the center of the fuel cap.  Despite squirting a lot of water at the cap with a hose, no more water in the tank.

Buy a new drain, run your tank down, remove the old drain and drain the tank completely.  Install new o-rings on the fuel caps, install the new drain, see what happens.

[carusoam]

Put a cloth in your hands, and wipe it around the top of the fuel neck... The side you can’t see...

See what the cloth looks like after that...

With the amount of junk that came out in the fuel sample cup...

It probably didn’t start rusting this week... or having the sealant degrade that quickly either...

 

If the plane is stored outside... 100% rh will aid corroding rustable surfaces... 60% rh can do the same... just a tad slower... it doesn’t have to be wet or be visible water...
 

The questions remain...

1) what is it?

2) how did it get there?
 

3) is it not coming back?

 

One of MS’ world traveling Mooneys got a load of fuel with junk floating in it... Screens packed up quickly after departure, making it questionable if getting back down safely was possible...

All worked out in the end...

The junk came from the fuel...

is that dirty rusty water at the bottom of the sample cup? Can’t tell from the pic... but, rust particles in water will look very similar to that...

Best regards,

-a-

[wishboneash]

Perhaps a chemical test for rust is worth trying out. Read about adding HCl (hydrochloric acid) to the what you have in the fuel drain and then observing for a yellow/green colour change after it dries out. Not a chemist, or an alchemist, but worth checking out online or with pros who may be more knowledgeable.

[LevelWing]

Thanks for the replies. I sumped it again this afternoon and it looks like sealant as it's a liquid, not rust flakes, as @N201MKTurbo suggested. I will try what @carusoam suggested and wipe the upper inside of the fuel tank and see what comes out as that's an easy thing to do. One step at a time. 

The plane has been hangared since 2014 and it wasn't until about two weeks ago that it was moved to an outside tie down. I'm hoping to get it back into a hangar by the end of the year, but we'll see.

[chriscalandro]

Here we go again with the fuel caps.  Just because you once had a problem with your fuel caps doesn't mean everyone's problem is the fuel caps.

 

It's a little bit of sealant that broke down when gas got put in it after sitting a long time.  No big deal.  Sump it out till it's clear and fly it.  If it develops a fuel leak, fix that and then fly it more.

[jlunseth]

The picture is a little hard to read, but I think you are getting water in your tank. There appears to be a thin liquid layer under the fuel. That is where you would find any water. Also, how are you going to get rust in a fuel tank without water to do the rusting? We just talked about this on another thread. The Mooney gas cap is recessed and therefore sits in a well that invites water to enter the tank around the gas cap. The only thing that stops the water is the O ring around the cap. If the O ring is cracked, water will come in with every rain. Now as I said, its not easy to read that photo, but it looks like a thin layer of a nonfuel liquid at the bottom of the cup. Water in the tank generally looks like a brown sludge because of bacterial growth and because the water can cause rust wherever it finds ferrous metal.

[Hank]

Be aware there are 2 o-rings in the fuel cap:  the large one you see every time you open the cap, and a tiny one (1/4" OD?) inside the cap that seals around the center pin from the flip cap.