Mooney Wing Tanks and Water

[GeeBee]

I have long suspected Mooney wing tanks hide water. I have confirmed it.

I took a trip to Jackson, TN (KMKL). I wanted a hangar for the two night stay, but none were available. Then due to circumstances not aviation related a two night stay turned into 4 nights. Not happy because bad weather was coming in on the third night. I begged for a hangar, but none to be had, so I strapped her down tight, covered all the ports including the fuel caps with those nifty covers from Wingviewtintshop.com and hoped for the best.

 

It was bad. Really bad. We had to evacuate our hotel room due to tornado warnings with sirens going off. I heard and saw big hail landing and my heart sank. I saw “walls of water” falling.  I returned to the airport fully expecting to see hail damage, but amazingly hail missed the airport. My fuel cap cover on the right cap was missing, and I was hopeful I had no water seepage because we just did an annual. In the annual we replaced the O-rings, big and small, did the ½ psi pressure test and it looked good. Looks are deceiving. 

 

I sumped both tanks. The left tank was clear of water. The right tank was water from the get go. Two GATS jars worth before I even begin to see blue. On the fourth, I had pure blue. I drained two more full GATS. I then shook the wing vigourasly and waited 10 minutes. Two more GATS jars and it seemed all was well… so it seemed.

 

I did not need the fuel in the right tank, I only needed 28 gallons to get home, so I flew home on the left tank, just to be sure. After placing the airplane in the home hangar, I sumped it again. About a tablespoon of water came out the right tank. I assume vibration aided the appearance. I sumped two more times which were clear.  I returned to the hangar the next morning. I sumped. No aggregated water but there were micro droplets on the side of the GATS jar. I cleaned the GATS jar with a paper towel. It took two more draws to get clean fuel. I returned the next morning, more micro droplets. Same procedure. On the third morning I finally had no micro droplets, but I was not convinced, so I “pasted” the tank with Gasoila and sure enough it showed entrained water. No visible droplets but it was positive for moisture.

 

At this point, I decided to drain the tank so I got a barrel and drained it with the boost pump. Easy peasy. Refueled with clean new fuel. Paste check showed good. I have plenty of gas for the lawn mower, so does the airport crew.

 

I write this because I have long suspected the Mooney wing hides water. It does. Even if you get a clear sample it takes a long time for all the water to work its way through all those little holes around the ribs and stringers. I had a very tight wing, resealed just two years ago by WetWingologists, pressure tested per the Mooney MM with no leaks, but the average wing cannot withstand buckets of water coming at it. You turbo guys who regularly fly below freezing may think you don’t have water, but a sump check is not sufficient. Might want to consider the 99% isopropyl treatment. Finally seal the tops of your caps if it stands in the rain. I had the covers and now I added velcro tape if I have to rely on them in windy weather. Be careful out there.

 

 

[EricJ]

I had a similar experience when I bought my airplane.   It had sat outside in a big storm before it was delivered here, and we were still sumping water while doing an initial inspection.   The airplane went from here to Maxwell's for a tank repair and more inspection.   We did some check flights at Maxwell's, during which time I was still draining small amounts of fuel unti clear before flying.   Just before returning to AZ the FBO had spilled some fuel and decided to hose the wings down to clean it up.    That resulted in a bunch more water in the tanks.  I just sampled fuel until no water was evident in the samples, but that kept happening for several flights after that, i.e., water would show up, drain until clear, etc.   It took a fair amount of time until I stopped getting water during preflight, but once it was gone, it was gone.    I changed out the cap o-rings and haven't had any issues since, but it hasn't really been outside in much rain, either.

Shaking the wing likely helps, but if you do see water it's worth keeping an eye on it for a while after that.

 

[Paul Thomas]

Did you get any water out of the gascolator?

[Fly Boomer]

59 minutes ago, GeeBee said:

I had the covers and now I added velcro tape if I have to rely on them in windy weather

So you affix one half of the Velcro tape to your wing, and the other half to the underside of your fuel cap covers?  How do you get that stuff off later?  I thought the adhesive they use was supposed to be semi-permanent.

[mike_elliott]

Sounds like the gas cap o rings on that tank are not sealing. The fuel vent and fuel servo are the only other paths into the tank for water. If the weep holes in the tank are seals over, water does get trapped. Anytime I spot water when sumping, I rock the culprit side wing fore and aft a number of times, resump, wait 5 min and resump. Repeat

ill start on that tank, run checklist, before taxi I’ll switch to known water free tank and do run up and take off on that tank. That way I have insured clean free flow from both sides on the ground

ymmv

[Fritz1]

sent me thinking, never had any water but will replace my small fuel cap O-rings since I do not know when this was done the last time and will put a a quart of isopropyl in to each tank every now and then to get rid of any traces

[Schllc]

had the rain event deposit water in my tanks as well.  now when i am on the ramp with a chance of rain i cover the caps, and the door jamb with blue painters tape.

super easy to remove before leaving, even if it its been in the sun a week.

[GeeBee]

2 hours ago, Paul Thomas said:

Did you get any water out of the gascolator?

No, but I never selected the affected tank either except to empty the tank.

[GeeBee]

2 hours ago, mike_elliott said:

Sounds like the gas cap o rings on that tank are not sealing. The fuel vent and fuel servo are the only other paths into the tank for water. If the weep holes in the tank are seals over, water does get trapped. Anytime I spot water when sumping, I rock the culprit side wing fore and aft a number of times, resump, wait 5 min and resump. Repeat

ill start on that tank, run checklist, before taxi I’ll switch to known water free tank and do run up and take off on that tank. That way I have insured clean free flow from both sides on the ground

ymmv

I don't know what more you can do beyond the Mooney MM pressure test, which as I wrote it passed. As a matter of fact, it exhaled the pressure after 15 minutes at 0.5 psi. Here is what I think. I think even if everything is tight the fuel caps cannot withstand a straight down deluge. Both the pressure test and in flight have a bulging wing. On the ground with massive amounts of water beating in the wing skin,  it depresses and allows water intrusion. 

Also you can operate normally with entrained water above freezing, but as several of our members have found, entrained water can result in a frozen spider in cold temps

[gabez]

14 minutes ago, Schllc said:

had the rain event deposit water in my tanks as well.  now when i am on the ramp with a chance of rain i cover the caps, and the door jamb with blue painters tape.

super easy to remove before leaving, even if it its been in the sun a week.

I have been dealing with this for a long time, posted in some other thread. I always put 8 inch blue tape on my fuel caps and the vent ports.

[dkkim73]

1 hour ago, Fritz1 said:

sent me thinking, never had any water but will replace my small fuel cap O-rings since I do not know when this was done the last time and will put a a quart of isopropyl in to each tank every now and then to get rid of any traces

Interesting point. I've used IPA when it was wicked cold but this is an interesting argument to use it to "mop up" periodically. I suppose before a big series of flights to decrease dwell time with the sealant. 

 

[dkkim73]

36 minutes ago, gabez said:

and the vent ports.

wondered about those, too. I almost thought about making rubber plugs with big "remove before flight" flags. 

[N201MKTurbo]

Have you checked AD 85-24-03? It may not have been properly complied with.

https://mooney.com/wp-content/uploads/2020/12/SBM20-230A.pdf

i have found that opening these holes is tedious. You cannot open them by just poking something through the holes. If you do the sealant will close the hole when you pull out the poker. You have to surgically remove the plug with the tip of an exacto knife like the SB says.

 

[GeeBee]

17 minutes ago, N201MKTurbo said:

Have you checked AD 85-24-03? It may not have been properly complied with.

https://mooney.com/wp-content/uploads/2020/12/SBM20-230A.pdf

 

Yes, as I mentioned, the tanks were resealed by WetWingologists East and I saw the tanks before they closed them up. They were compliant and of course a professional operation such as WWE would as you expect be familiar with the AD.

[N201MKTurbo]

8 minutes ago, GeeBee said:

Yes, as I mentioned, the tanks were resealed by WetWingologists East and I saw the tanks before they closed them up. They were compliant and of course a professional operation such as WWE would as you expect be familiar with the AD.

Did you dump about a gallon of water into the tank and watch it drain out? It can be deceiving.

Do you have a better explanation of why they are retaining water? This is the obvious answer. 

[GeeBee]

9 minutes ago, N201MKTurbo said:

Did you dump about a gallon of water into the tank and watch it drain out? It can be deceiving.

Do you have a better explanation of why they are retaining water? This is the obvious answer. 

Because not all water in fuel becomes free water. It can take a long time and a lot of circumstances for all water in fuel to become free water.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC20-125.pdf

[N201MKTurbo]

Ok, but that applies to all airplanes and both tanks. If you have one tank that holds more water than the other, it most likely has plugged drains.

[M20F]

@GeeBee don’t you use your own rings?  I have had zero issues since installing years ago.  I suspect you have something else going on. 

[GeeBee]

1 hour ago, N201MKTurbo said:

Ok, but that applies to all airplanes and both tanks. If you have one tank that holds more water than the other, it most likely has plugged drains.

Both drains drop fuel at the same rate and they are two year old drains. Again, if you read my narrative, it drained the free water no problem. It is the entrained water that is the problem and I suspect most people on this board if presented with a fuel sample of entrained water could detect it is there. In fact anybody who uses those "screw driver" type sump tubes will not see it.  That is what makes the GAT jar the bomb.

From AC120-25

For this reason, a water

haze may be seen in turbine fuel but the haze is seldom seen in aviation

gasoline. 

[Greg Ellis]

18 minutes ago, M20F said:

@GeeBee don’t you use your own rings?  I have had zero issues since installing years ago.  I suspect you have something else going on. 

I think you are referring to @Gee Bee Aeroproducts, not @GeeBee

[00-Negative]

I made some fuel tank covers recently and tried them out this past weekend. I parked outside in north Arkansas for the weekend where we got plenty of rain. My covers stayed on and kept the water out perfectly. 

I used magnets that stick to the steel center post of the fuel cap. I cut 1/16" abs plastic which I heated to form a concave shape. I tested it in place with a 200mph blower. 

https://www.amazon.com/dp/B085NP6SQY?ref=fed_asin_title

 

-David

[M20F]

32 minutes ago, Greg Ellis said:

I think you are referring to @Gee Bee Aeroproducts, not @GeeBee

The GeeBee’s need to meet. 

[GeeBee]

6 minutes ago, M20F said:

The GeeBee’s need to meet. 

We have!

[N201MKTurbo]

But have either one ever flown a GeeBee?

[M20F]

8 minutes ago, GeeBee said:

We have!

Go blue, it will fix your problem.  
 
Water is annoying.  When it freezes at the bottom  of your tank, that’s when the real fun happens.  
 
@Gee Bee Aeroproducts to the rescue.