Water in fuel?? Am I imagining it?!

Here’s a puzzler for the group.

I picked up my Arrow from the shop yesterday after it was sitting out in the sun on his ramp for a week in the very hot sun. When I checked the tanks looking for water that may have come in through the fuel caps ( it rained heavily this past week), I saw the following….

Wing Sumps- No water and a Good BLUE color. True in both fuel drains. BLUE both.

Front Gascolator- ALMOST CLEAR. Very slight blue tint. It looked SCARILY clear to me- even when I held it up to the white airplane!! Almost no blue!

I refused to fly it, and had an A&P look at it. He drained it some more and said it was not water. All fuel. How could that be?

it looked almost clear!!

Can ANYONE give me a reason why the fuel from the front Gascolator ( near the engine) does NOT come out as blue as from the tanks?

My worry of course is that the NEXT time I see almost clear liquid coming from the front Gascolator I will assume it’s nothing when that will be the time it WILL BE all water?

Any A& P’s have a reason for the huge color change from wing fuel to Gascolator fuel?

I’m stumped.

Thanks Group

N9091Y Scott KPNE


  • Hi Scott,

    you definitely did the right thing!

    Since water is about 35% more dense than avgas, and the gasco is at the "bottom" of your fuel system, any water that makes its way in through the caps will eventually find its way down to the gasco. My guess is that when you sumped the gasco you removed all the water, such that when your mechanic repeated the process, there was nothing left for him to find.

    Did you go back and sump the gasco again after your mechanic did?


  • Not yet. I pick it up Monday and m hoping I see more blue!

    Stay tune and I’ll report back.🙏

    Thanks for the feedback.

  • N9091Y;

    Get 2 gas cups. Capture some gas from the wing. Capture roughly the same amount in the other gas cup from the gascolator. Pour them on the tarmac at the same time and watch the evaporation. Water takes much longer to evaporate than gasoline, and will be a positive indicator that you have water in the fuel.

    Jim "Doc Griff" Griffin
    PA28 - 161
    Chicago area

  • Good plan. I’ll try it!


  • Scott and Jim,

    This discussion reminded me of an old magic trick you can use to amaze a first-grader, especially one you're trying to get interested in math & science.

    To perform the trick, you'll need (1) a GATS jar, (2) a Sharpie, (3) a kitchen scale that reads in grams (owned by a wife who doesn't ask too many questions), and (4) a first-grader - you can borrow mine for as long as you want! Oh, and (5) an airplane that's been sitting outside for a while.

    Mark a fill line on the GATS jar near the top with the Sharpie; the exact location isn't critical. Then zero the scale with the empty jar on it, and have your first-grader sump the Gasco and place the jar back on the scale. You'll probably get a reading around 285-ish grams. Empty the jar (not into the plane-that'll ruin the trick) and repeat the sumping and weighing, being sure to fill it exactly to the same fill line. This time you'll probably see a reading around 260 grams.

    Once his amazement dies down, ask him why the second sample is lighter. And, double or nothing, "if you sample the Gasco a third time, or the wing tanks, what result do you expect to get?"

    Then take him for those $200 pancakes! And try to sneak the scale back in the house without getting caught...


  • I’ll give it a try!


  • Too funny :)

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

    Need help? Let me know!

  • I have a 9 grader I will throw in.

    @griff390 is wise also.

    Don't listen to me, I suggest using a lighter. Only fire will prove it is gasoline.

    1973 Arrow II factory AC removed

    G5’S, G275, GNX375 Still can get lost.

  • What about the testers with a specific gravity ball?

    Learned to have faith in the ball as one time when I sumped, the ball floated, yet the color was just as blue as expected. Tell-tale sign of confirmation (aside from the floating ball) was that there was a hint of mixed liquids at the top of the sample. A few samples later and the ball no longer floated.

    For the pour and evaporation test, just a thought as passed along to me from a CFI. Pour on to concrete. Doing so on blacktop will lead to pits at the pour site.

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