Water In Fuel (and lots of it...)
 

I just bought my first skymaster, a 1973 P model. Bought it on the West coast and flew it back to the East coast the end of last week. I drained the sump drains to include rocking the wings after each of the 3 times I filled the tanks and had no evidence of water. I did have a steady drip fuel leak coming from the right sump drain after one of the times I drained it so when I got back I had my mechanic look at it and he recommended replacing the drain. Doing this required that he drain the fuel out of the wing. There was probably 20 gallons in the tank. To both of our surprise, probably 1/3 (yes, a third) of what came out of the tank was water!

The engine ran great, for the entire 3 leg/ 8 hour trip East. I am baffled as to (1) why water did not come out when I drained the tanks, and even more so (2) how the engine ran so well. The drain valve was corroded (probably because it was sitting in water) which is what caused the fuel leak. The plane has not been hangared the past 6 months or so, but water has not touched the airplane since I picked it up.

So while I'm curious why I did not see water and why the engine ran great, I really want to make sure I stop the water from getting in the tank in the future. I ran water through the overflow vent at the fuel fill cap this morning and it went straight through. That may not guarantee there is not a leak there, but it seemed to work well.

What about the access panels on top of the wing? Any chance that could be the source of water intrusion?

Any help would be greatly appreciated!

Thanks,
Paul

That is an interesting issue. As for the test on the tank drain, if you are referring to the service port drains you need to check them again. Here is the method I use:

First, use Avgas, there might be a leak and you don't need to introduce more water into the tank.

While introducing the Avgas to the service port drain, have a second person plug the drain below the wing to be sure there is no cracks or leaks that would allow intrusion of liquid into the tank.

Your model has a different fuel system than mine. Mine has a sump in the boom and that is where the fuel sump is. Cessna eliminated this sump in the boom and I will need to take a closer look at the diagram to remind myself of the system.

Thanks.

I did as you suggested this morning, with one person plugging the drain and using fuel poured around the service panel. The fuel level stayed unchanged and did not appear to leak into the tank, so no indication of a leak based on that test.

Given that the drain appears to work well, it seems unlikely that if water got around the service panel that it would have gone through the seal of the fuel cap without draining out through the hole?

I checked the other access panels on top of the wing and did not see any evidence of any possible water intrusion at other points in the tank.

I don't know where else it could have gotten in.

Only other idea I have is that maybe I could have pumped bad gas?? My last stop coming home was in Fayetteville Arkansas where they had a cheap self service pump. I filled the left tank first and then started filling the right tank, but while pumping the fill rate got very slow and eventually stopped. I assumed it was out of gas so I went to the FBO and had them finish topping me off. The water that came out of the right tank was relatively dirty and makes me wonder if perhaps when that self serve pump ran dry if I was getting the "junk" that was left? Maybe it was all stirred up so the engine ran okay and after sitting several days it finally separated out?

The corroded fuel drain led me to think that water may have been in the tank for some time, but that has to be a coincidence. Other than stirred up bad gas, I can't come up with another reason why the engine could have kept running.

I've been out of general aviation for a while so I'd be interested in any other thoughts on what might have happened.

I can't dismiss your theory. It is definitely possible and not completely rare. With the sequence you are describing it sounds really possible. I have had intrusion of water from a pump once that I remember. Sometimes I purposely allow a little fuel to over spill in the service port to visually see the fuel and if there are any signs of contaminates. Be careful because fuel spills these days are like big red flags at some of these places. Sure glad you didn't have any problems during the flight. Consider yourself very fortunate.

I read this and went Wow! New Fuel Type!

Paul, it is my experience that just a little water will make an engine run rough (drops), 7 gallons a side would kill them dead. I'm wondering if when you drained the tanks it actually separated or if there was lighting or other characteristic's such as lack of or breakdown of dye that caused you to believe it was water? I also own a 73P, if there are no fuel stains on the upper wing skins after you fuel it, there is no leak. The way they overlay would prevent water entry. Welcome to the club, Best of luck with your new Skymaster!


Brent

Hopefully the attached picture shows up. What you see is the separation of one bucket that came out of the tank (there were 5 more with probably 1/3-1/2 of the bucket "separated"). Avgas is on the top, the dark line is where the water (or whatever it was) separated to the bottom.

This was the right tank and I had the selector properly selected to have the right tank going to the rear engine.

I did 8 hours of flying from California to South Carolina with a fuel stop in ABQ and one in Fayetteville, AR. I sumped the tanks and ran the engine drains each time.

Interestingly, out of California my front engine had some "moments" with fuel flow dropping for short periods of time, but it seemed to run just fine for the last 4-5 hours of flying. The rear engine seemed to run fine.

When I got to SC I did not add any fuel and made arrangements to get the mechanic to immediately deal with the slow leak from the sump drain. It was only when he called me to tell me what he had drained out (have to drain the tank to replace the sump drain) and then had me come look at the buckets that this all came up.

The plane had an annual inspection in November after sitting for about 6-8 months outside (California dessert) and it flew about 6 hours after the annual inspection.

In my mind, I either got some bad gas in Fayetteville that was suspended enough to not cause the engine to quit, or perhaps I had it all the way from California and each time I filled up (right before I flew) it stirred it up and allowed it to be suspended. I did call Fayetteville yesterday and alerted them this may have happened. They called back and said they tested their sumps and other checks and did not see a problem, though I doubt they would admit if they had.

The water (or other separated substance) was very dirty, but we have run some clean fuel through the tank and drained it and the tank appears clean so it had to have been pumped in.

I'm looking for the "ah-ha" moment on this but have not got it yet.

Looking at the pic, I'm not having an aha moment either, but if it was water it would be clearer, my guess is you got some of the "bottom of the barrel" at the self service fuel stop. My best guess is rust sediment from old in ground tanks. Hopefully the new fuel will flush it out and you will have no problems.

Water in your Avgas
 

Paul,

Based on your last refuel in Arkansas, I believe that is where you took on the water. The fuel flow slowing down then completely stopping, tells me the pump filter system became laden with water from the tank, thus shutting down the flow. Also called "no-go" filters, these types of filters are supposed to stop the flow of fuel should they have water get in them. Perhaps it was this type of filter medium, however it did not react as fast (maybe an older filter).

Jeff

Jeff,

I think you have to be right. It is just amazing the "substance" seemed to work fine in the engine. I flew yesterday and carefully sumped the tanks multiple times with perfect fuel. No problems so hopefully no problems. Going to keep the plane in a hanger but will watch for water intrusion, but I don't think that was my problem. The fuel drip from the drain turned out to be a blessing that allowed me to catch the bad gas in the tank. Yes, I'll be on the front row at church this morning...