Water in the tanks

[druidjaidan]

I've had my K model for a bit over a year now and we're heading into our second annual with the plane. For most of the time we've owned it we've dealt with water getting into the tanks. Not a terribly small amount, like a half a GATS jar or more of water, per tank. We squawked it at the last annual and the mechanic also noted it when they pulled it in.  Based on the logs they did the normal changing of the orings.  However, the issue persisted this last year. Even had a scary encounter where we pulled basically an entire GATS jar out, shook the wings a bunch, let it settle pulled more out and repeated until it was all fuel. Only to fly it for a short flight to lunch and resump to another half a GATS jar of water.

We're back into annual inspection again, and I squawked it again, but I have lower confidence that anything more than the normal annual o ring change will really be done.

Are there options to solve this for real? I had my F model for nearly a decade sitting out on the ramp and never pulled more than a couple drops from the tank (likely just from opening the cap in our rainy Seattle weather).

[MikeOH]

Other than the caps (O-rings) leaking, I'm not sure what other path water has into the tanks.  Are you certain they changed BOTH O-rings? If they missed the small O-ring on the shaft, that would do it!  If you have the caps I'm envisioning with the lift up handles, you could try the following: with the cap off the plane but in the locked (handle down and flush), poor some water into the top recess (where the handle folds into) and see if water leaks out the bottom around the shaft.

[Fly Boomer]

16 minutes ago, druidjaidan said:

We're back into annual inspection again, and I squawked it again, but I have lower confidence that anything more than the normal annual o ring change will really be done.

As crazy as it sounds (the practice -- not the suggestion), the suggestion from @MikeOH is a good one.  I have previously read of the practice of only changing the easy-to-get-to big ring, and never changing the hard-to-get-to small ring.  Even if the o-rings are good, the tension on the center shaft must be correct or they will leak.

[PeteMc]

Agree that BOTH rings need to be changed.  But is there any chance you're getting water when you get fuel?  

I checked the tanks one time before a flight, flew around a bit using both tanks, and landed at a different airport to get fuel.   I don't rush to check for water after filling and always check the first tank I filled.  I pulled huge amount of water out of the first tank I had filled, none out of the other.  No idea how long it had been since the last person used the pump at this airport, but obviously they had water in the tank that settled by the time I used it. 

 

[druidjaidan]

Unlikely the fuel souce as my home base (and where I buy most of  my fuel) is a major airport (KPAE) with multiple active schools burning fuel. If they are getting water out of the pumps that would be caught super fast and resolved. I can't imagine that they would be pumping water for over a year. I'm also just pulling water out before I even go refuel so it's almost certainly the caps.

I'd hope the mechanic would replace both o-rings, especially since we both noted lots of water was getting in. It is an MSC, so that shouldn't be weird to him.

Edited May 27, 2025 by druidjaidan

[Skyland]

Fuel selector to OFF.  Connect a rubber hose to the fuel vent and blow into it to slightly pressurize the tank.  Check the cap seal with a soap solution.

SBM20-229A.pdf

[Ragsf15e]

10 minutes ago, druidjaidan said:

Unlikely the fuel souce as my home base (and where I buy most of  my fuel) is a major airport (KPAE) with multiple active schools burning fuel. If they are getting water out of the pumps that would be caught super fast and resolved. I can't imagine that they would be pumping water for over a year. I'm also just pulling water out before I even go refuel so it's almost certainly the caps.

I'd hope the mechanic would replace both o-rings, especially since we both noted lots of water was getting in. It is an MSC, so that shouldn't be weird to him.

I have a K as well.  Last annual my IA told me to replace one of the newer blue flourosilicone O rings because it was a little loose.  So I dutifully ordered new ones for both caps and went to work (supervised).  Having done it before on my F, it only takes ~15minutes per cap, but lo and behold, the inner O ring on both caps was the old black kind?! The plane has been maintained before I bought it by big name MSCs but apparently they just changed the outer O ring?!

Also, do you have long range tanks?  I wonder about those caps.  They feel a little flimsy but they’re supposed to be ok?

[Fly Boomer]

53 minutes ago, Ragsf15e said:

Also, do you have long range tanks?  I wonder about those caps.  They feel a little flimsy but they’re supposed to be ok?

This confuses me.  All 4 of my caps are identical.

[druidjaidan]

49 minutes ago, Ragsf15e said:

I have a K as well.  Last annual my IA told me to replace one of the newer blue flourosilicone O rings because it was a little loose.  So I dutifully ordered new ones for both caps and went to work (supervised).  Having done it before on my F, it only takes ~15minutes per cap, but lo and behold, the inner O ring on both caps was the old black kind?! The plane has been maintained before I bought it by big name MSCs but apparently they just changed the outer O ring?!

Also, do you have long range tanks?  I wonder about those caps.  They feel a little flimsy but they’re supposed to be ok?

 

No long range tanks, the airplane tanks already outlast my family's tanks as it is =)

I might go buy a set of the blue flourosilicone rings and see to it that they are replaced if we are still leaking after this annual

[MikeOH]

1 hour ago, druidjaidan said:

 

No long range tanks, the airplane tanks already outlast my family's tanks as it is =)

I might go buy a set of the blue flourosilicone rings and see to it that they are replaced if we are still leaking after this annual

Why not just ask the shop to give you the 'old' parts (i.e. both the large and small O-rings) after annual?  If the small ones are black, you'll have your answer

[GeeBee]

3 hours ago, druidjaidan said:

I've had my K model for a bit over a year now and we're heading into our second annual with the plane. For most of the time we've owned it we've dealt with water getting into the tanks. Not a terribly small amount, like a half a GATS jar or more of water, per tank. We squawked it at the last annual and the mechanic also noted it when they pulled it in.  Based on the logs they did the normal changing of the orings.  However, the issue persisted this last year. Even had a scary encounter where we pulled basically an entire GATS jar out, shook the wings a bunch, let it settle pulled more out and repeated until it was all fuel. Only to fly it for a short flight to lunch and resump to another half a GATS jar of water.

We're back into annual inspection again, and I squawked it again, but I have lower confidence that anything more than the normal annual o ring change will really be done.

Are there options to solve this for real? I had my F model for nearly a decade sitting out on the ramp and never pulled more than a couple drops from the tank (likely just from opening the cap in our rainy Seattle weather).

This might help

 

[Ragsf15e]

5 hours ago, Fly Boomer said:

This confuses me.  All 4 of my caps are identical.

Interesting.  My outer tanks have smaller, lockable caps (with a key).  I’ll see if I have a picture…

not the best photo but you get the idea…

[1980Mooney]

2 hours ago, Ragsf15e said:

Interesting.  My outer tanks have smaller, lockable caps (with a key).  I’ll see if I have a picture…

not the best photo but you get the idea…

This is off topic for the OP, but your outboard extended range filler cap does not look like it is installed per the Monroy instructions.  My outboard filler cap, like yours, is also smaller than the factory OEM main tank cap, however the filler cap adapter ring should be mounted under the skin of the wing (inside the tank).  Your adapter ring appears to be on top of the skin of the wing. 

I have the Monroy Installation manual and drawings.  I can see how someone might misread the instructions, but the drawing is clear.  Also, the hole will not be large enough for the outside of the taper on the adapter plate.  I think that is why yours looks like it is not even flush with the outside skin of the wing.

Here is a picture of the inside of the main filler adapter plate mounted on the inside of the tank.  The adapter plate (ring) is clearly visible on the inside.  It creates a cleaner, almost flush installation.

Look at this other installation on a K.

Outboard extended tank filler - notice that it is flush and the cap adapter ring is under the skin of the wing.

Edited May 28, 2025 by 1980Mooney

[Fly Boomer]

8 hours ago, Ragsf15e said:

Interesting.  My outer tanks have smaller, lockable caps (with a key).  I’ll see if I have a picture…

Don't know.  Maybe some were not done by Jose, or it was a customer-requested upgrade.  Maybe depends on what year the tanks were done.  I wish mine were lockable.

[Ragsf15e]

6 hours ago, Fly Boomer said:

Don't know.  Maybe some were not done by Jose, or it was a customer-requested upgrade.  Maybe depends on what year the tanks were done.  I wish mine were lockable.

They were the last long range tanks done before the stc was Sold to maxwells.  Done by wet wingologist east (in conjunction with full strip/reseal), so Im pretty sure he knows the stc.  Not sure why they are different.  

[Slick Nick]

50 minutes ago, Ragsf15e said:

They were the last long range tanks done before the stc was Sold to maxwells.  Done by wet wingologist east (in conjunction with full strip/reseal), so Im pretty sure he knows the stc.  Not sure why they are different.  

Those are supposed to be attached from the underside of the upper wing skin. They were installed incorrectly. Probably costing you some speed also. 

[Marc_B]

FWIW, I have Monroy long range tanks (installed/signed off by Jose Monroy according to the log), and the necks are installed under the skin with the cap flush with the skin.  I've not seen any applications where it was mounted above the skin.

[Ragsf15e]

13 minutes ago, Slick Nick said:

Those are supposed to be attached from the underside of the upper wing skin. They were installed incorrectly. Probably costing you some speed also. 

They appear to be the same as these…

[gabez]

23 hours ago, druidjaidan said:

I've had my K model for a bit over a year now and we're heading into our second annual with the plane. For most of the time we've owned it we've dealt with water getting into the tanks. Not a terribly small amount, like a half a GATS jar or more of water, per tank. We squawked it at the last annual and the mechanic also noted it when they pulled it in.  Based on the logs they did the normal changing of the orings.  However, the issue persisted this last year. Even had a scary encounter where we pulled basically an entire GATS jar out, shook the wings a bunch, let it settle pulled more out and repeated until it was all fuel. Only to fly it for a short flight to lunch and resump to another half a GATS jar of water.

We're back into annual inspection again, and I squawked it again, but I have lower confidence that anything more than the normal annual o ring change will really be done.

Are there options to solve this for real? I had my F model for nearly a decade sitting out on the ramp and never pulled more than a couple drops from the tank (likely just from opening the cap in our rainy Seattle weather).

I had an engine stopped working on me (while flying) in my M20K, I spent thousands of dollars and eliminate the problem after the damage the water caused. In my case the Monroe tanks sump valve was not at the lowest point of the tank thus I couldn't not sump the fuel/water and eventually found its way through the fuel system, which I ultimately had to rebuild including gascolator, fuel selector, electrical pump, flow divider, mech pump and all the bits in between. Since then no water in the tanks. 

Basically, make sure the sump valve is posited at the lower point, mine wasn't . 

Edited May 28, 2025 by gabez

[Ragsf15e]

1 hour ago, Slick Nick said:

Those are supposed to be attached from the underside of the upper wing skin. They were installed incorrectly. Probably costing you some speed also. 

I agree about the speed!  They are mounted iaw the manufacturer instructions though.  They are Newton aero  300 caps.  Now whether or not they are approved?  Dunno, but they are the same as the ones Brian Kendrick mounted on @Schllc ‘s airplane.

[Schllc]

They are legal, and are the same caps used on everything from sometime in 2008 until the end of production. I didn’t notice any speed penalty after my install. 
Brian made a doubler the exact size of the collar of the old style and riveted the new one together and I don’t even think he had much to reseal.  You won’t be able to tell after paint. 
I had them on a few other planes and really miss them. 
the replacement caps are cheap, don’t damage the paint when you lay it on the wing, they don’t leak water. 

[Pinecone]

Hmm, does installing them get rid of that stupid spring loaded flap????

[Fly Boomer]

17 minutes ago, Pinecone said:

Hmm, does installing them get rid of that stupid spring loaded flap????

That alone would be worth the price of admission.

[Ragsf15e]

14 hours ago, Schllc said:

They are legal, and are the same caps used on everything from sometime in 2008 until the end of production. I didn’t notice any speed penalty after my install. 
Brian made a doubler the exact size of the collar of the old style and riveted the new one together and I don’t even think he had much to reseal.  You won’t be able to tell after paint. 
I had them on a few other planes and really miss them. 
the replacement caps are cheap, don’t damage the paint when you lay it on the wing, they don’t leak water. 

I looked them up on Spruce.  They are used on Cirrus and Columbias.  Aero 300 by Newton.  

[Pinecone]

5 hours ago, Fly Boomer said:

That alone would be worth the price of admission.

That is what I was thinking