Does The Mooney Wing Tank Hide Water?

[EricJ]

4 hours ago, jlunseth said:

This puzzles me because I have had my plane for 13 years now and never any water. Zero. So much so that I have to work to keep the discipline to sump after every new fuel load. There was a period maybe a decade ago where for about a year I put isopropyl in for most flights. The recommendation was to do that in turbos because at high altitudes even during the summer we are flying constantly in temps that are well below freezing, but I never saw a problem and have discontinued the practice. If I had water hiding in the tanks it might have gotten cleaned out while I was doing that, and never returned. The biggest problem is the O rings for the fuel caps. The caps sit in a slight well, as everyone knows, and if the plane is outside when it rains, water pools up in that well and will find its way into the tanks. I flew a J some years ago that had quite a bit of water in it for that reason. My caps are in good shape and I have kept them that way, so no water. Just have never seen any at all. No engine stumbles because of it either. I fly in the rain quite a bit in the summer too.

Paul Beck at Weep-No-More redid my tanks 13 years ago. Did a superb job and maybe the quality of the reseal leaves fuel no place to hide.

A big difference may be keeping the plane in a hangar. Except when I am on a trip somewhere, the plane is always hangared. It is not rained on much, maybe a few times a year.

Based on that experience I wonder if your fuel source has water in the tank so you are constantly having some introduced? Might want to talk to them.

When I bought my airplane it was being held hostage in a four-month-long never-ending annual inspection because the IA "kept finding things", but he never replaced the rotted large o-rings on the fuel caps.   "Didn't have those in stock."    The airplane was parked outside during some large rainstorms and the tanks got a ton of water in them, so much so that the ferry pilots that were hired to bring it down here could only get water and no fuel out.    They got the IA that had been working on it and he broke the sump valve off trying to remove it to drain the water.   So they left the airplane and somebody else eventually brought it down.

@N201MKTurbo then ferried it from here to Maxwell's for the PPI and we drained some more water out, including from the gascolator, before sending him off to Texas.    When I picked it up I did my insurance checkout and noted that it had huge fuel stains down the wings from around the fillers, which I let the FBO know about.    They washed it down thoroughly, because the wings were still wet when I left the next morning.   I think this introduced some more water, as the o-rings still had not been replaced.

From that point I always did the usual process of just drain the sump until you get a sample (or two or three) with only fuel.   For the next few weeks and dozen hours or so I always got some water out, and just drained it until I got only fuel.   One day it quit on takeoff just as the gear was coming up and I had only just enough runway left to get it back down again.   That was when Rich suggested shaking the wings vigorously, which got a bunch more water out, and then I've never seen any again after that.

There's also the possibility of getting water pumped with the fuel, especially from fuel trucks.   An instructor friend did the impossible turn in a C150 with a student after it quit on takeoff, and they found that the fuel truck had a LOT of water in it and a bunch got pumped into the airplane.   They didn't see any during preflight inspection.   Edit:  I might be remembering that wrong and that might have been one of the cases where they saw no water bubbles because it was all water.

There are a lot of ways it can happen.   My airplane has been hangared since I bought it, and I still always sump the tanks because of the possibility of water being introduced from the fuel pump.   Doubly so if it got stored outside, triply so if outside during rain.

[GeeBee]

When I was a young Captain,  I had a B737-200 in KELP that had these new STC'd electronic fuel gauges. They would not read out a quality but instead an error code. The code it was announcing was "fuel contamination". The mechanics sumped the snot out of the airplane but still had a code. We ran a millapore test on the sump fuel, and it came up clean. I sent a mechanic to the fuel truck to investigate. He came back and said he found a sweater floating in the tank. The truck had maintenance and the worker inside that tank took off his sweater because his coverall over it made him to warm. The fibers and dye that was not trapped by the sumps and thus the Millipore test never would have picked it up. 

[jetdriven]

3 hours ago, EricJ said:

From that point I always did the usual process of just drain the sump until you get a sample (or two or three) with only fuel.   For the next few weeks and dozen hours or so I always got some water out, and just drained it until I got only fuel.   One day it quit on takeoff just as the gear was coming up and I had only just enough runway left to get it back down again.   That was when Rich suggested shaking the wings vigorously, which got a bunch more water out, and then I've never seen any again after that.

There's also the possibility of getting water pumped with the fuel, especially from fuel trucks.   An instructor friend did the impossible turn in a C150 with a student after it quit on takeoff, and they found that the fuel truck had a LOT of water in it and a bunch got pumped into the airplane.   They didn't see any during preflight inspection.   Edit:  I might be remembering that wrong and that might have been one of the cases where they saw no water bubbles because it was all water.

There are a lot of ways it can happen.   My airplane has been hangared since I bought it, and I still always sump the tanks because of the possibility of water being introduced from the fuel pump.   Doubly so if it got stored outside, triply so if outside during rain.

If shaking the wings frees up more than a trivial amount of water, I would wager the drainback holes in the ribs are plugged with sealant, and the aircraft does not conform to AD 85-24-03.

[EricJ]

1 hour ago, jetdriven said:

If shaking the wings frees up more than a trivial amount of water, I would wager the drainback holes in the ribs are plugged with sealant, and the aircraft does not conform to AD 85-24-03.

The aircraft was just out of a long annual at another shop plus a PPI from Maxwell and had the AD marked as compliant, but that is entirely possible.

[jetdriven]

We've had a few planes marked as compliant, and we opened up the wings to seal a couple of minor leaks, and they were sealants smeared with what looks like gloves and fingers by the pint everywhere. And I showed the owner rhis And I say this  can get you killed. you can pump a gallon of water in the airplane and it won't reach the sump but After takeoff it will.  Hopefully you opened up the tanks and inspected the drain holes, because an AD compliant airplane could not trap more than a few oz of water. 

[EricJ]

47 minutes ago, jetdriven said:

We've had a few planes marked as compliant, and we opened up the wings to seal a couple of minor leaks, and they were sealants smeared with what looks like gloves and fingers by the pint everywhere. And I showed the owner rhis And I say this  can get you killed. you can pump a gallon of water in the airplane and it won't reach the sump but After takeoff it will.  Hopefully you opened up the tanks and inspected the drain holes, because an AD compliant airplane could not trap more than a few oz of water. 

When the airplane was at Maxwells for the PPI they did a tank repair and had the left tank open at that time.   If there were significant issues I suspect they would have noted something.   I did have the tanks inspected for debris and anything else after a servo failure not long after all of the water issues, and they didn't note anything, either, other than they were clean.

I've not personally done a detailed inspected because I've not seen any water in it in four-plus years. 

[Mac80]

Related but not same issue.

I had stutter at below freezing that was intermittent but had a skipping variable loss of fuel pressure at same time. Happened mostly on right tank.

I believe it was due to air leaking past fuel selector seal. Heard that Maxwell has recommended lube the selector which I did with silicone spray.

Also may ask mechanic to replace them but for now it has not come back.

 

[carusoam]

In most new Mooneys after a year of ownership… before the first annual is completed… it is unlikely to have water hiding in the tanks…

So many things can change after that….
 

What we know about most Mooney fuel tanks… (M20Ks have a few too many variations…)

1) The tanks have ribs with a few holes to allow fuel through in the bottom part of the rib…

2) The top part of the ribs have the same holes to allow air to pass through…

3) Sometimes the holes get blocked with sealant….

4) The holes are not at the exact top or exact bottom of the ribs…. If water gets in, it can be hard to drain out, without chemical assistance…

5) Old Orings are a hassle….

6) wrong oring type can easily absorb fuel and the orings stop working…

7) There are two orings per cap… small and large….

8) Caps can leak rain water in after an annual if the mechanic insists on checking the inner oring…. Without knowing how to reset the proper tightness of the cap’s tab…

9) The blue Teflon based orings seem to last a very long time… minimizing the oring checking maintenance induced error…

10) when you have a leaky fuel cap in the rain… you will see air bubbles growing up through the cap… in flight!

11) when water does get in the tank… know the altitude order of the tank parts…

• cap
• fill neck
• air or head space…
• Bulk of gasoline
• close to the bottom is the fuel pick up screen
• at the bottom is the sump… there are a few sump drain issues… wrong drain, sealant covered side drain holes, drain installation, etc…
• Really important… below the drain is an area of the tank that the drain couldn’t fit in.  The lowest corner of the rectangular shaped tank…
• Soooo when you drain the tank using the sump drain, and water comes out… there is still a spoonful of water below the drain…

12) All our chemists and chemical engineers are familiar with water dissolving in gasoline… it is a small amount, But… it is temperature dependent… and some can fall out of solution with wide temperature swings… combined with 50gallons of fuel in each tank… this can be an issue.

13) Adding cold temperature to the discussion… fuel and moisture evaporating…in a cold system… can lead to ice crystals building as fuel vapor continues on…

14) Old Mooneys have mild steel used as a fuel neck… water vapor collects behind the fuel neck and rusts over the decades… takes about 40 years to rust through… the stress of metal forming aids the corrosion… the holes form at the cracks that appear…. When manufactured, these areas were covered in paint on the outside. Over the years the paint sheds off the mild steel… usual solution for this, install SS fuel necks… easy update.

15) Adding fuel additives is covered in the Mooney POH for modern Mooneys…

16) adding chemicals to the fuel system is always going to get a level of concern… much of the concern is around long term contact with rubber and plastic parts… use the additive, and then use up all of the fuel… don’t let it sit in the tanks for long term storage…

17) Consider shutting down after using the tank with the least possible amount of additive in it… if one tank had less than the other… there is only a few minutes of fuel in the system down stream of the fuel selector switch…

18) As Byron mentioned above… seriously consider what happens as the plane changes attitude… if there is moisture in the tank that didn’t leave after sumping… it may move around when the plane changes attitude… or slips or skids…

19) Fuel vents are always interesting… the LBs got large diameter vents hidden in reversed NACA ducts… nicely hidden from view… Perfect for the mud daubers to hide a blockage…

My M20C had the mild steel fuel necks that rusted through…

My M20R had the fuel caps mis adjusted at an annual that showed the air bubbles forming in the rain…

First year of M20R ownership… I got the visit from the mud daubers… mud daubers are generous creatures… they even visit inside the hangars… 

PP thoughts only, not a mechanic or a chemist…

Best regards,

-a-

[ArtVandelay]

To protect against mud daubers or other insects clogging my fuel vents:

[Fly Boomer]

1 hour ago, ArtVandelay said:

To protect against mud daubers or other insects clogging my fuel vents:

Okay, just to let you know, I'm straight up stealing that idea.  I like it!

[jlunseth]

This is interesting. I have had not problems with water and I shake the wings often. I don’t shake them trying to get water out, I never thought of it that way. I shake them whenever I am taking a long trip and want to be sure I have absolutely full tanks. I don’t shake them vigorously because that causes big air bubbles to come out, spraying fuel on the wings, more like rythmically. Don’t know that would make any difference. During the summer flying season I probably do this two or three times a month. If it helps, maybe we have hit on something. It probably also helps that more than half of my fuel comes from Thunderbird, at Flying Cloud, and they have quite a bit of fuel sales volume, so in the 13 years I have been there I have never seen fuel in the tank of my K, just in that J I flew a decade or so ago that had bad O rings.

I still sump every single time.

[Pinecone]

One thing I saw on another forum for the vents is use a pipe cleaner.  Fold in half and insert.  Keep the mud daubers out, but if you forget them, air can still vent past it.

A lifetime and then some supply for $6. 

https://www.amazon.com/dp/B08KVYZKTX?ref=ppx_yo2ov_dt_b_product_details&th=1

 

 

 

[Fly Boomer]

6 minutes ago, Pinecone said:

One thing I saw on another forum for the vents is use a pipe cleaner.  Fold in half and insert.  Keep the mud daubers out, but if you forget them, air can still vent past it.

A lifetime and then some supply for $6. 

https://www.amazon.com/dp/B08KVYZKTX?ref=ppx_yo2ov_dt_b_product_details&th=1

 

 

 

With memories of these from long ago, I would have thought a pipe cleaner would be too skinny, but maybe "Chenille" means they are fatter.  Good safety precaution.

[Mooney in Oz]

On 1/9/2023 at 6:17 PM, carusoam said:

install SS fuel necks… easy update.

What is a SS fuel neck?

[Mooney in Oz]

On 1/8/2023 at 11:56 PM, Pinecone said:

If you are parked outside, there are fuel cap covers to keep the water out of the cap well.

https://wingviewtint.com/products/fuel-cap-covers

 

 

I just ordered a pair.  Thanks for the suggestion. 

 

[RoundTwo]

21 minutes ago, Mooney in Oz said:

What is a SS fuel neck?

Stainless Steel

[RoundTwo]

On 1/9/2023 at 6:03 AM, ArtVandelay said:

To protect against mud daubers or other insects clogging my fuel vents:

First thought was Ouch!!!

[A64Pilot]

17 hours ago, Mooney in Oz said:

I just ordered a pair.  Thanks for the suggestion. 

 

$60 fuel cap covers.

The attached pic is the correct fuel caps for a Cessna C-140, the fuel tank vent is two holes in the cap. You can imagine how well they keep water out in a real rainstorm.

What I use is I bought two of the cheapest toilet plungers you can buy, $5 ea of so, they have red rubber cups and a screw in wooden handle, unscrew the handle and place the rubber cups over the fuel tank cap, they are pretty heavy so they stray in place in at least 40 MPH winds, but being rubber they don’t hurt anything if you forget them. (it’s a high wing and out of sight)

Walmart has them for $1.78 and Lowes about $3.50 

https://www.lowes.com/pd/Cobra-5-in-dia-Rubber-Plunger-with-18-in-Handle/1001868092?cm_mmc=shp-_-c-_-prd-_-plb-_-ggl-_-LIA_PLB_208_Plumbing-Repair-_-1001868092-_-local-_-0-_-0&ds_rl=1286981&gclid=CjwKCAiA2fmdBhBpEiwA4CcHzXkMDaimMRKFkeb_no9DdLQhL_R_x8HUtHbcTW8-1dpnsmsCSrO5KRoCUaIQAvD_BwE&gclsrc=aw.ds

[Mooney in Oz]

On 1/9/2023 at 10:03 PM, ArtVandelay said:

To protect against mud daubers or other insects clogging my fuel vents:

I’ve had the same setup for about the past 15 years. Prior to that each vent had a very small screen covering the outlet until they somehow disappeared.

[Shadrach]

On 1/9/2023 at 6:03 AM, ArtVandelay said:

To protect against mud daubers or other insects clogging my fuel vents:

Why is your fuel tank vent placarded as a fuel drain? Not that it’s dangerous, just seems silly.

[mike_elliott]

On 1/9/2023 at 6:03 AM, ArtVandelay said:

To protect against mud daubers or other insects clogging my fuel vents:

Putting a piece of safety wire in the vent will really discourage a mud dauber, and it wont "fall" out or climb into the tank. Leave 1/4" sticking out of the vent tube for ease of removal if you want.

[T. Peterson]

On 1/9/2023 at 1:17 AM, carusoam said:

In most new Mooneys after a year of ownership… before the first annual is completed… it is unlikely to have water hiding in the tanks…

So many things can change after that….
 

What we know about most Mooney fuel tanks… (M20Ks have a few too many variations…)

1) The tanks have ribs with a few holes to allow fuel through in the bottom part of the rib…

2) The top part of the ribs have the same holes to allow air to pass through…

3) Sometimes the holes get blocked with sealant….

4) The holes are not at the exact top or exact bottom of the ribs…. If water gets in, it can be hard to drain out, without chemical assistance…

5) Old Orings are a hassle….

6) wrong oring type can easily absorb fuel and the orings stop working…

7) There are two orings per cap… small and large….

8) Caps can leak rain water in after an annual if the mechanic insists on checking the inner oring…. Without knowing how to reset the proper tightness of the cap’s tab…

9) The blue Teflon based orings seem to last a very long time… minimizing the oring checking maintenance induced error…

10) when you have a leaky fuel cap in the rain… you will see air bubbles growing up through the cap… in flight!

11) when water does get in the tank… know the altitude order of the tank parts…

• cap
• fill neck
• air or head space…
• Bulk of gasoline
• close to the bottom is the fuel pick up screen
• at the bottom is the sump… there are a few sump drain issues… wrong drain, sealant covered side drain holes, drain installation, etc…
• Really important… below the drain is an area of the tank that the drain couldn’t fit in.  The lowest corner of the rectangular shaped tank…
• Soooo when you drain the tank using the sump drain, and water comes out… there is still a spoonful of water below the drain…

12) All our chemists and chemical engineers are familiar with water dissolving in gasoline… it is a small amount, But… it is temperature dependent… and some can fall out of solution with wide temperature swings… combined with 50gallons of fuel in each tank… this can be an issue.

13) Adding cold temperature to the discussion… fuel and moisture evaporating…in a cold system… can lead to ice crystals building as fuel vapor continues on…

14) Old Mooneys have mild steel used as a fuel neck… water vapor collects behind the fuel neck and rusts over the decades… takes about 40 years to rust through… the stress of metal forming aids the corrosion… the holes form at the cracks that appear…. When manufactured, these areas were covered in paint on the outside. Over the years the paint sheds off the mild steel… usual solution for this, install SS fuel necks… easy update.

15) Adding fuel additives is covered in the Mooney POH for modern Mooneys…

16) adding chemicals to the fuel system is always going to get a level of concern… much of the concern is around long term contact with rubber and plastic parts… use the additive, and then use up all of the fuel… don’t let it sit in the tanks for long term storage…

17) Consider shutting down after using the tank with the least possible amount of additive in it… if one tank had less than the other… there is only a few minutes of fuel in the system down stream of the fuel selector switch…

18) As Byron mentioned above… seriously consider what happens as the plane changes attitude… if there is moisture in the tank that didn’t leave after sumping… it may move around when the plane changes attitude… or slips or skids…

19) Fuel vents are always interesting… the LBs got large diameter vents hidden in reversed NACA ducts… nicely hidden from view… Perfect for the mud daubers to hide a blockage…

My M20C had the mild steel fuel necks that rusted through…

My M20R had the fuel caps mis adjusted at an annual that showed the air bubbles forming in the rain…

First year of M20R ownership… I got the visit from the mud daubers… mud daubers are generous creatures… they even visit inside the hangars… 

PP thoughts only, not a mechanic or a chemist…

Best regards,

-a-

Now, that was thorough!!