Water in Fuel

[Palmpilot]

I recently rented a Piper Dakota and had trouble with engine roughness, which seemed to get worse during the flight. Carb heat did not help, and checking for plug fouling on the ground did not reveal any evidence of that.

After the flight I wrote it up, and the owner came to the airport a few days later to check it out. He found about a cup of water in the right tank, which is the one that I used for about the first hour of the 1.3 hour flight. He subsequently made a test flight and experienced no roughness, so the water seems like a sufficient explanation, especially since there was a major rainstorm a few days before my flight.

The puzzle is that I clearly remember sampling the fuel in both tanks during preflight, and I remember that the samples which were clear, uniform, and the correct color. The day of my flight was clear and dry. So my question is, what ways are there that the water could have failed to show up in the preflight fuel sample?

One thing this experience has done is heighten my awareness of the possibility of water in the fuel even when none shows up in the fuel sample. I wish it had occurred to me to try switching tanks. (I need to be more consistent about using checklists!)

 

[eman1200]

Back in the day I rented a Cherokee 140. An instructor and student brought the plane back from a short flight. I sumped….and sumped….and sumped….every time it was FULL of water in one tank. After about the 4th or 5th time I waved the instructor over and showed him. He was in awe and swore up and down that he watched his student do the preflight which included sumping the tanks. And I believe him, this was an extremely thorough CFI. So, I guess it can happen, unfortunately.

 

[jrollf]

Does the Dakota have fuel bladders? Could be a fold in the bladder trapping water.

Sent from my SM-N960U using Tapatalk

 

[Salty]

Also could have been caught in a wing rib if not a bladder. When I find any water I get it all out, then rock the plane as much as possible and sump again. One time I did that half dozen times before I stopped getting water.

 

[Palmpilot]

Does the Dakota have fuel bladders? Could be a fold in the bladder trapping water.

Sent from my SM-N960U using Tapatalk

There's no mention of bladders in the POH.

 

[Datadriver]

If the plane was not level when sumped it may not have drained the water properly during your preflight.

After a heavy rainstorm at OSH one year I had to empty my tester twice to clear out the water, that was also a P28 - Arrow.

 

[Palmpilot]

Also could have been caught in a wing rib if not a bladder. When I find any water I get it all out, then rock the plane as much as possible and sump again. One time I did that half dozen times before I stopped getting water.

There was a lot of turning during my flight, so it is conceivable that it could have sloshed the water over a rib, if there are any.

 

[bflynn]

Also it if was recently filled when you sampled, the water may not have settled out yet.

 

[Palmpilot]

If the plane was not level when sumped it may not have drained the water properly during your preflight.

After a heavy rainstorm at OSH one year I had to empty my tester twice to clear out the water, that was also a P28 - Arrow.

The pavement where the plane parks seems level.

 

[Palmpilot]

Also it if was recently filled when you sampled, the water may not have settled out yet.

It was probably refueled within a day of its previous flight, which was a couple of weeks before mine.

The plane is kept fueled to the tabs, which leaves 11 gallons of air above 25 gallons of fuel in each tank. One thing I was wondering was whether the air in the tank could have been humid enough to form condensation as the plane climbed. (I noticed dew on the plane's cover when I took it off.) Although that wouldn't explain why no water was found in the other tank.

 

[Dan Thomas]

It was probably refueled within a day of its previous flight, which was a couple of weeks before mine.

The plane is kept fueled to the tabs, which leaves 11 gallons of air above 25 gallons of fuel in each tank. One thing I was wondering was whether the air in the tank could have been humid enough to form condensation as the plane climbed. (I noticed dew on the plane's cover when I took it off.) Although that wouldn't explain why no water was found in the other tank.

11 gallons of air is 1.48 cubic feet. At 59°F that air can hold only .0008 pounds of water when the air is at 100% humidity. That's .0067 cups of water. You'd need a tank airspace of over 1600 gallons to hold a cup of water, and you'd have to get ALL the dry air out of it somehow and replace it with saturated air. Normal thermal changes can't achieve anything like that. Condensation isn't your problem. Mostly it isn't anyone's problem whether in fuel tanks or engine crankcases. Leaky fuel caps let water in. Water can accumulate over a long time, or get pumped into the tank from a contaminated supply, and not get drained if the tank geometry lets it get trapped in places, or if the airplane isn't sitting properly. Flat nose oleo, maybe. Sloped ramp. Whatever.

Major rainstorm a few days before your flight is a red flag. Those tank caps need checking.

 

[Palmpilot]

11 gallons of air is 1.48 cubic feet. At 59°F that air can hold only .0008 pounds of water when the air is at 100% humidity. That's .0067 cups of water. You'd need a tank airspace of over 1600 gallons to hold a cup of water, and you'd have to get ALL the dry air out of it somehow and replace it with saturated air. Normal thermal changes can't achieve anything like that. Condensation isn't your problem. Mostly it isn't anyone's problem whether in fuel tanks or engine crankcases. Leaky fuel caps let water in. Water can accumulate over a long time, or get pumped into the tank from a contaminated supply, and not get drained if the tank geometry lets it get trapped in places, or if the airplane isn't sitting properly. Flat nose oleo, maybe. Sloped ramp. Whatever.

Major rainstorm a few days before your flight is a red flag. Those tank caps need checking.

Wow, thanks for that analysis!

 

[Tools]

I recently had this issue in a 152... sump like crazy, nary a drop of water. Fly an hour, take a half cup out of the gascolator. It put me in a field actually...

I still have no clue why it couldn’t be sumped out. Rocked, sat the tail down, all sorts of stuff. I wonder if the tank isn’t bent pretty badly on one side.

So yes, sumping isn’t a guarantee... glad it didn’t put you down somewhere!

 

[Dan Thomas]

I recently had this issue in a 152... sump like crazy, nary a drop of water. Fly an hour, take a half cup out of the gascolator. It put me in a field actually...

I still have no clue why it couldn’t be sumped out. Rocked, sat the tail down, all sorts of stuff. I wonder if the tank isn’t bent pretty badly on one side.

So yes, sumping isn’t a guarantee... glad it didn’t put you down somewhere!

You tank bottom might be pushed upward at the drain. That aluminum tank is light and soft and aggressively pushing on the drain valve might distort it. The tail needs to stay down for the draining, too, or the water could just run forward again. Those tanks are pretty flat-bottomed. And the airplane tends to sit in an attitude that leaves the tank bottom too level. You can lift the nose of that airplane by lifting on the prop blades, close to the spinner, and kicking a wooden block under the nosewheel.

Slipping the airplane in flight, or some turbulence, can move the water to the fuel outlet and you'll see it at the gascolator.

Tests on a 150:
http://www.sumpthis.com/cessna150andcessna152tanktest/cessna150tanktestimages1024x768.htm

 

[chemgeek]

Tell me you did go through the whole potential engine failure routine at the first onset of persistent roughness? Not just carb heat, but mag check, full rich mixture, energize fuel pump, switch tanks, check primer locked, etc.

BTDT, but my roughness episode led to an engine stoppage, which was reversed 30 seconds after going through the engine problem routine. Probably saved an off-airport landing. Likely cause was water or ice in the tank and/or carb icing.

 

[Tools]

Ya, no. Happened at 150’ on takeoff... Not a lot of troubleshooting going there, mostly busy not crashing into stuff.

Turned most of the way around and found about 500’ of pasture after slicing through a tree line. Best looking 500’ of open space I EVER laid eyes on. Got her set down and stopped, no damage whatsoever.

 

[Palmpilot]

Tell me you did go through the whole potential engine failure routine at the first onset of persistent roughness? Not just carb heat, but mag check, full rich mixture, energize fuel pump, switch tanks, check primer locked, etc....

As I said in post #1, "I need to be more consistent about using checklists!"

 

[chemgeek]

As I said in post #1, "I need to be more consistent about using checklists!"

From experience, I wouldn't rely on checklists. You won't have time to get it out and read it during an emergency especially at low altitude. Practice the necessary flow. For my plane, there is a pretty simple left to right flow from mag switch, fuel pump, carb heat, mixture, primer, tank selector. Touch them all and hope one of them reverses the problem. I was glad I had practiced that in advance when my engine started barfing.

 

[Palmpilot]

From experience, I wouldn't rely on checklists. You won't have time to get it out and read it during an emergency especially at low altitude. Practice the necessary flow. For my plane, there is a pretty simple left to right flow from mag switch, fuel pump, carb heat, mixture, primer, tank selector. Touch them all and hope one of them reverses the problem. I was glad I had practiced that in advance when my engine started barfing.

That's the engine failure procedure that I was taught. It probably didn't occur to me to use it because I didn't actually have an engine failure, but now that you mention it, it is obviously appropriate to this situation as well.

 

[midwestpa24]

The puzzle is that I clearly remember sampling the fuel in both tanks during preflight, and I remember that the samples which were clear, uniform, and the correct color. The day of my flight was clear and dry. So my question is, what ways are there that the water could have failed to show up in the preflight fuel sample?

I'll just throw this out there, but are you sure your sample was not 100% water? We are so used to seeing that line or bubble between the fuel and water, and I've seen the water seem to be tinted slightly blue either because the sample cup was stained or perhaps some of the blue dye had mixed with the water?

 

[Dan Thomas]

.....or perhaps some of the blue dye had mixed with the water?

That has been known to happen.

 

[MajorTurbulence]

I'll just throw this out there, but are you sure your sample was not 100% water? We are so used to seeing that line or bubble between the fuel and water, and I've seen the water seem to be tinted slightly blue either because the sample cup was stained or perhaps some of the blue dye had mixed with the water?

I’ll just re-emphasize this point. If your sample was all water, no line would be visible until enough water was drained from the tank. I’ve had this happen in my Archer after a rain with leaking gas gaps. It may not be so easy to see the blue tinge when biased towards thinking that it is there in a homogeneous sample )A night time preflight would also make it difficult to discern the blue tinge).I’m not sure what tipped me off to drain some more to actual prove there was a fuel/water line after all.

Also, besides looking at the color, I also smell the sample since I’m also worried about jet fuel contamination at the FBO if not actually witnessing the full-up.

 

[AKBill]

I'll just throw this out there, but are you sure your sample was not 100% water? We are so used to seeing that line or bubble between the fuel and water, and I've seen the water seem to be tinted slightly blue either because the sample cup was stained or perhaps some of the blue dye had mixed with the water?

I have had that happen. Took several samples I did not like the looks of. After about 5 samples I was happy I got all the water out. Flush fuel caps, changed all the o-rings

 

[Palmpilot]

I'll just throw this out there, but are you sure your sample was not 100% water? We are so used to seeing that line or bubble between the fuel and water, and I've seen the water seem to be tinted slightly blue either because the sample cup was stained or perhaps some of the blue dye had mixed with the water?

Yes, I'm sure.

 

[Domenick]

Besides smelling the sample, a quick finger dip and how fast it evaporates will also inform.