Leaking fuel caps

[ArrowBerry]

Hey guys,

I recently took our 67E on an overnight trip in which it rained while the aircraft was tied down outside. We nearly never park outside, the airplane lives inside and as a result, the next day when I sumped the tanks to leave I was surprised at the amount of water. On both sides there was an entire cup of water that I took out before I even started getting the 50/50 mixtures where you could clearly see the blue av gas floating on top. 

Presumably for those of you who park outside regularly it not normal to pull out that much water after only a single night. How can we fix this? Is it just a matter of replacing the O rings from Laser? When I looked at the caps I realized that they are slightly recessed into the wing. It seems like an odd design considering that it encourages water to collect right on top of the fuel cap. 

[N201MKTurbo]

Replace the o-rings and adjust the tightness. Mine don’t leak.

[Rmnpilot]

There’s a Service Bulletin for the fuel caps/ orings as well. 

M20-229A.pdf

[carusoam]

Rich has nailed exactly what the issue is…

Rmn has captured the most detail in one place…

 

Add that water can collect on top of the cap… it can be blown away pretty easily…. And a paper towel can handle the rest…

Wait until you have this challenge on a below 32°F day…  
 

Find @OSUAV8TER see if he still has the sets of orings that fit our fuel caps…

Know that there are two orings per cap… small and big.

Know how tight is too tight… and how loose is too loose… it is a fine balance of one turn of the nut….

Know that there is still water below the fuel drain… there is a dry gas additive that is proper for Mooney fuel tanks to use… for that tsp amount….

PP thoughts only,

-a-

[Jim Peace]

7 minutes ago, carusoam said:

there is a dry gas additive that is proper for Mooney fuel tanks to use… for that tsp amount….

PP thoughts only,

-a-

Due tell….

[carusoam]

15 minutes ago, Jim Peace said:

Due tell….

Two parts to that question…

1) the fuel tank extends an inch in two directions… behind and beside the fuel drain… the tank extends into that corner… and that corner is lower than the fuel drain itself…

2) Some planes have the wrong fuel drain, or it’s holes May be plugged…. Causing other water issues than normal…

3) The ‘dry gas’ is an alcohol that is an approved additive for Mooneys… to be used with the appropriate ratio… often gets used in winter months because there is a tiny amount of water that is dissolved in fuel naturally…. And can fall out of solution in the flight levels as fuel gets vaporized… and gets left behind forming ice in important places near the fuel injection system…

let’s see if we can find the reference… and brand name…

looks like isopropyl alcohol may be it… finding it with 0% water in it would be better than rubbing alcohol…. That has more water in it already….

Prist may make a version that is more aircraft ready…

https://www.sportys.com/prist-hi-flash-hi-flo-anti-icing-aviation-fuel-additive.html

(answers are really non-descript, as I am not a mechanic giving proper advice…)

Best regards,

-a-

[carusoam]

oddly,

I searched on isopropyl… around here and found nothing…

The Google search…
 

-a-

[Jim Peace]

Just don’t want to use anything that would mess up my new tank sealant. 

[N201MKTurbo]

I would be careful adding alcohol to our tanks. I don’t think the sealant likes it.

[kortopates]

Isopropyl Alcohol is approved by Mooney for this purpose. PRIST/EGME is not recommended since its not good for the fuel system. This is covered in most later POH's Limitations section with upto 3% which is way more than ever needed. A small amount goes a long ways in absorbing any left over water.

Edited August 14, 2022 by kortopates

[Yetti]

get the fluorosilicone O rings.   It's a safety thing.

[BobbyH]

I also found when installing new O-rings to use some fuel resistant lubricant like EZ Turn.  It extends the life of the O-rings and makes it much easier to open the caps, not to mention that it will help seal the cap. 

[ArtVandelay]

Put some painters tape over them, this is helpful in the winter when water will freeze. I recommend doing this for those with speed brakes as well.

[skykrawler]

This is fundamental knowledge every Mooney owner must have. 

[ArrowBerry]

Thanks for the responses! I was able to source the small blue fluorosilicone O rings from a member on here and they are on their way already. Spruce only has the regular black O rings, and Amazon.ca has the larger fluorosilicone rings for $35 each. Does anyone know of a better place to order them or should I just go ahead and grab them for $35? Seems like a lot, although I suppose not actually that much compared to most airplane parts...

[Rmnpilot]

This is what I used for my caps.   Not sure specifically for the “E” models    This included everything I needed  

https://www.ebay.com/itm/322645237730?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=r4qr2gQVT5K&sssrc=2349624&ssuid=Qkj22W-nTzC&var=&widget_ver=artemis&media=COPY

[N201MKTurbo]

I’m sure the new fancy o-rings are the bomb, but for the last 40 years, I just order the ones from the parts manual 5 at a time. At every annual I look at the o-rings and if they look sad or weather checked, I replace them. The big One takes all of 30 seconds to change, the small one takes a couple of minutes. 5 of the big ones cost less than $10 and will last 10 years or so. I know everybody has a better idea of what is best, but it isn’t a problem that needs solving. 

[Guest]

M25988/1-010 and M25988-1-338 blue or MS29513-010 and MS29513-338 black nitrile.  The small 010 of either type wear out first allowing water in.  From SB M20-229A pressure check your cap for proper sealing, a length of 1/4” surgical tubing pushed over your vent a small squirt of soapy water and your lungs are all you need.  
 

NO SHOP AIR!

[PT20J]

7 hours ago, M20Doc said:

M25988/1-010 and M25988-1-338 blue or MS29512-010 and MS29512-338 black nitrile.  The small 010 of either type wear out first allowing water in.  From SB M20-229A pressure check your cap for proper sealing, a length of 1/4” surgical tubing pushed over your vent a small squirt of soapy water and your lungs are all you need.  
 

NO SHOP AIR!

Did you mean MS29513?

[Guest]

5 hours ago, PT20J said:

Did you mean MS29513?

You’re correct, I fat fingered it. MS29513 series is correct.

[LANCECASPER]

19 hours ago, ArrowBerry said:

Thanks for the responses! I was able to source the small blue fluorosilicone O rings from a member on here and they are on their way already. Spruce only has the regular black O rings, and Amazon.ca has the larger fluorosilicone rings for $35 each. Does anyone know of a better place to order them or should I just go ahead and grab them for $35? Seems like a lot, although I suppose not actually that much compared to most airplane parts...

Talk to James Gallagher @OSUAV8TER or go to his website gallagheraviation.com

EDIT: or go James' Ebay buying site that Ryan @Rmnpilot mentioned above (https://www.ebay.com/itm/322645237730?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=r4qr2gQVT5K&sssrc=2349624&ssuid=Qkj22W-nTzC&var=&widget_ver=artemis&media=COPY)

[OSUAV8TER]

I carry the blue flourosilicone o-ring fuel cap kits and most Mooney aircraft need my Shaw 431/531 fluorosilicone o-ring kit. They are $14 a kit and I have them in stock. They come with the large and small o-ring, along with a new cotter key. I have had the original fluorosilicone o-rings on my fuel caps of my Bonanza for 7 years with no signs of deterioration and I have left the aircraft out in heavy rain with no fuel contamination. 

You can order them off my website at https://www.gallagheraviationllc.com/products.html

Also consider the Marsh Brothers GF polymer washer kits. Your current fuel cap washer is a stainless steal ring that wears down your plunger making it challenging to close properly and more difficult to open and close. These things are a little pricey but they are miracle works. Most Mooneys need the -2 kit that comes with 2 washers.

 

[RobertGary1]

20 hours ago, ArrowBerry said:

Thanks for the responses! I was able to source the small blue fluorosilicone O rings from a member on here and they are on their way already. Spruce only has the regular black O rings, and Amazon.ca has the larger fluorosilicone rings for $35 each. Does anyone know of a better place to order them or should I just go ahead and grab them for $35? Seems like a lot, although I suppose not actually that much compared to most airplane parts...

The seals should be replaced annually. No need for long lasting seals that get tossed at annual anyway. 

[OSUAV8TER]

15 minutes ago, RobertGary1 said:

The seals should be replaced annually. No need for long lasting seals that get tossed at annual anyway. 

You do not have to toss fluorosilicone o-rings on an annual basis.  I don't understand why you would install buna-N o-rings that immediately start to break down and have to be replaced on an annual basis over a difference of $10 a cap? 

[LANCECASPER]

13 minutes ago, RobertGary1 said:

The seals should be replaced annually. No need for long lasting seals that get tossed at annual anyway. 

M20-229A says that the seals should be inspected annually. I've seen the spec'd seals show cracks in a year.

I put the flourosilicone seals that I bought from @OSUAV8TER in my Bravo in 2016 and they still looked and performed like new in 2021 when I sold the airplane. They had been inspected at every annual and passed. I was there for the pre-buy in November 2021 and the A&P showed my seals to the prospective new owner and said, "This guy "gets" it - these are the seals everyone should be using." My Acclaim does not use the Shaw fuel caps but if I had an airplane that used the Shaw caps I would never go back to the old style seals.