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How to be certain fuel sample isn’t all water?

Asked by: 2584 views , ,
General Aviation, Private Pilot

Often the 100LL fuel at my airport is so lightly tinted that it does not appear blue. I sump multiple times and smell the fuel. Still I'm sometimes unable to see a blue tint and I'm concerned I'm looking at all water. 

Is is there a way to be certain it's fuel and not all water I'm looking at? Perhaps I could add a little water to the sample to verify the difference from the fuel?

 

Thanks

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1 Answers



  1. Skyfox on Jul 11, 2016

    Yes, that’s one way to do it. Water settles to the bottom of avgas like it would with oil, so if you add a couple drops of water to the sampler and see those same drops sitting at the bottom, you know it’s not a cup of water you’re looking at. Another test is to simply splash the sample cup onto something and observe how quickly it evaporates. Avgas will evaporate very quickly, while water would evaporate very slowly (or hardly at all on a humid day).

    One thing you have to be sure of is that it is in fact 100LL you’re getting. The dyes in the various grades of avgas are formulated to neutralize each other and turn clear if they’re mixed. Double check with the FBO that it is in fact 100LL they get at that pump and that they test it before the storage tank is filled. If the fuel supplier is doing the job right, they have a bucket with a white porcelain lining that they dump a sample of their shipment into for inspection by the delivery person as well as the FBO attendant. In that very white bucket, the blue dye of 100LL stands out quite clearly, especially in sunlight. If it was a different grade they should see it very plainly and reject the shipment.

    Those little plastic samplers aren’t perfect for sampling because, IMO, the plastic has a very slight blue tint to it already. Something else you can do is hold up the sample cup with a white sheet of paper behind it to help the color stand out, and maybe even pour it into a clear glass jar if you want to eliminate the possibility of a slightly tinted plastic.

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