Water in tank
 

About 3 or 4 years ago the 1979 C337H I fly was sleeping outside the hangar and with a rain of about 40 mm (near 2 inches) I drained about 8 drain cups of water from teh left wing.
I notice the new to the mechanic and he said that fixed the problem, but last anual 2 weeks ago I got about 4 drain cup from the outside drain point of the left wing.
Does anybody know if there is any modification to avoid this problem again ?
Thank you

Not sure on the newer models like yours but there is a drain at the service cap for the tank on my '68 that will drain any fuel that overflows during fueling. This drain is a small 1/8 inch tube that passes through the tank before exiting over board under the wing. If there is any corrosion in that tube inside the fuel tank moisture from atop the wing will pass down around the service door to the tank and drain out through that tube. If the tube is bad the moisture deposits in your fuel cell.

Just a place to check.

The photos show the door over the service port and the door open at the service port. Notice the small hole (drain) at the upper left of the photo. This is the tube that passes through the tank and exits under the wing.

I know the answer
 

There are a few ways water can get in the tanks. The fill ports sit in little 'swimming pools' that will fill with rain water, UNLESS:

Periodically replace the seals around the base of the fuel caps; when they dry out over the years, the encourage water to seep into the tanks past them.

Also, I keep some long pipe cleaners in my toolkit. It is imperative that the thru-wing drain holes are clear. I also drool a bit of fuel around the fill with every filling, to make sure these drains are clear. If not, I stop and clear them with the pipe-cleaners.

....I learned this the interesting way,...having experienced a front engine cutoff on rotation out of a 2600 ft runway in a valley one time....

somewhere there is an ad to change the fuel caps to one that do not pool water around the
fill cap to prevent water getting into the tanks. i remember changing mine years ago

In 2008 I lost my 2nd 337 to the same problem you are having. Over several years, a number of mechanics replaced gaskets, fuel caps, cleaned drains on my aircraft ectra, ectra, etra. Each time saying that “the problem had been fixed”. In July of 2008 after a four day trip to Branson Mo, and four days I might add, of the heaviest rains I can recall Witnesses verified that I carefully preflight my aircraft for our return home. I check and rechecked, drained and redrained the sumps, remembering everything I have ever read regarding Cessna’s and water related problems reported over the years, and yes I even raised and lowered, shook and wiggled the wings. With all of that, I only drained about 3 oz of water out of my left wing. I thought I was good to go. After a normal run up, we were set to depart lookout point Mo. We accelerated normally. However just as mains started to break ground, and without warning, the front engine quit. Aux pumps didn’t help, and the aircraft quickly settled back to the runway. The accelerates stop distance proved to be marginal, but I thought workable. A blow out tire later, this proved not to be the case. At about 5 knots, we slid of the end of the runway, and down the @50’ bolder covered drop off. We experienced a total lost, but walked away with only minor injuries.
The faa discovered over a gallon of water in the left wing, and no fuel was present from the wing to the spider on the front engine. To this date it remains undetermined where the water was trapped, but the faa did find that the scupper drain tube (the one that drains overflow from around the filler) had a small crack that was leaking water into the fuel tank. How is this possible? On my 1977 337G, this tube didn’t just pass from the drain through the wing. Instead this tube ran from the drain through the fuel tank then out the bottom of the wing. It was my understanding the crack was in this area. I am not saying this is what you are experiencing, but I might be worth a look!

Gary
The same scenario I was describing here. When we had the SOAPA fly in last year at Branson we based at Point Lookout and your incident was brought up by several pilots around the airport at Point Lookout.

The way that I checked my tubes that drain from the service port to the underside of the wing (yes these pass through the tank on all skymasters) was to seal the bottom side of the tube under the wing and add fuel to the tube from the top at the service port to see if the fuel stays in the tube or releases somewhere between. I did this with some of the tanks out of the wing but this could be performed with the tanks in place on the aircraft.

It is good to know that you and your passengers were able to walk away from this incident and I respect your choice to tell the story so that maybe someone else does not have this issue.

This is the AD that has to do with the fuel caps

http://rgl.faa.gov/Regulatory_and_Gu...ment#_Section1