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3 Answers

C150 water in fuel

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Aircraft Systems

Fueled up a Cessna 150 on a Friday evening.  Waited a few minutes, sumped both tanks, and found dirty water in the sample from the left wing tank.  All three subsequent samples from that wing were clean, even after rocking the wings, so we went to go fly.

Fueled up this same Cessna 150 the following day (Sat).  Found the same dirty water contamination (approximately the same amount, too) in the left wing.

There was no precipitation on Friday evening.  Also, the tanks were nearly full after the Friday flight so I don't think condenstation was the issue.

I decided to scrub the Saturday flight because there was no obvious reason why more water should have appeared in the same wing after having taken a clean sample on Friday, under the good assumption that the fuel source is clean.  My concern was that water is collecting somewhere which is not being drained by the sump, and perhaps adding the fuel was enough to slosh things around so that I saw the water in my sample.  This seems to be a known issue with the Cessna 150 and other models (see www.sumpthis.com), but I have no proof that this was the issue.  

Am I being overly conservative about this or is the repeating issue (over two successive flights) enough of a cause for concern?  What actions can I take to be sure that my fuel tank is clear of contaminants?  Any other similar experiences?

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3 Answers



  1. Wes Beard on Mar 27, 2013

    The density of the fuel is affected greatly by its temperature. On really cold days the water will be absorbed into the fuel while on warmer days the water will come out of solution. Doesn’t explain why the fuel was dirty but explains the presence of water.

    You did exactly what you were supposed to do. The advisory circular talking about fuel sump procedures recommends several minutes after sumping and finding water before sumping again. again if you find water again, repeat the process till only fuel comes out.

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  2. John D. Collins on Mar 27, 2013

    Don’t eliminate the distinct possibility that the water was pumped into the tank with fuel that was contaminated with water. There are filters and testing devices that the FBO is required to have to verify they don’t have water in their fuel. Check that their tests are current.

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  3. Sam Dawson on Mar 27, 2013

    I had a situation in a C-150 with fuel in the tank. In my case it was caused by a bad gasket on a fuel cap permitting rain to enter the tank.
    What I found was that REALLY getting all the water is a two person operation. Drain the fuel as normal until there is no water. Then have someone push the tail down to tilt the airplane- drain again. If there was water in the first sample, there may well be water again. Do this until clear. Rock the wings back and forth. Repeat.
    This is also a good time to point out that the CPA (Cessna Pilot Association), recommended procedure for draining fuel differs from the check list. It recommends draining the wing sumps, then the sump(s) under the nose. This is due to the gravity feed system. If you drain the nose prior to one of the tanks you may be drawing water into the fuel lines.

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