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When you sump, you should look for more than just water in your fuel. Here are 5 things you should look for.

1) Water In Your Sump Cup

Water is the most common contaminant in aviation fuel. Because water is denser than 100LL, you'll find water settling to the lowest part of the tank. When you see it in your sump cup, it will look like clear bubbles (or a clear layer) at the bottom of the cup.

2) Cracked Fuel Caps

When the filler neck of a fuel tank isn't sealed properly by a fuel cap, water can seep in. After heavy rain, you could find a significant amount of water in your tanks if you have bad seals.

3) Clogged Sump

If your sump point won't drain, you may have contaminants in the fuel large enough to clog the drain hole. There could be a problem with the drain mechanism itself, too.

4) "Koolaid" Blue Avgas Color

Avgas is usually a light blue color. If you sump the tanks of an airplane and the color is initially a deep, dark blue, you make have a slow leak. If the leak around the drain is slow enough, the blue dye from the avgas can build up at the drain port, causing the avgas to come out unusually blue compared to gas from another tank.

After a few sumps, the color will generally return to normal. Get your plane inspected by a mechanic for possible leaks.

5) Incorrect Fuel Types

If you have someone fuel your plane, check the fuel receipt to confirm the correct fuel was put on your aircraft before you take off. This is something we do every time we get full-service fuel.

Have you ever noticed a problem with your fuel on preflight? Tell us about your experience in the comments below.

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