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Lesson learned... Gascolator checks and sump drains may not suffice.
It is hard to describe the feelings of surprise, relief, and bewilderment yesterday when we found out what an awful mess has been lurking inside my main fuel tank. To me... this is enough to cause me to NEVER use mogas ever again in an airplane. I guess that its ok if you fly regularly, but here's what can happen if you let mogas stagnate and set in your fuel tanks. This discovery yesterday came as a surprise because we recently thoroughly cleaned and flushed out the fuel tank during annual inspection. Since the annual, I have flown exclusively with avgas for around 8 hours with no hint of a fuel contamination problem. And I check and drain the gascolator before each flight. There has not even been one speck drained out on any flight. Same went for yesterday's pre-flight. I might have continued with this major problem unknowingly had I not made a unusual decision yesterday.
I was about to make an hour-long flight and I was debating about whether to plan a stop for fuel. The fuel float indicator was showing maybe a little less than half (I was thinking maybe 5 or 6 gallons). So I asked Lon (my father in law) to borrow the dipstick he has for his '39 tcraft. (This was the unusual decision.) It is a wood stick with a notch at every 2 gallon increment. So I dropped it down to the bottom of the tank to check the quantity. As the stick contacted the tank bottom, there was a distinct feeling that there was something else in the tank besides fuel. It felt like a layer of salt or sand... maybe a half inch deep laying in the bottom. Needless to say, I decided not to fly.
Lon and Travis helped me figure out what to do. We decided to rig up a siphon tube and see if we could vacuum it out. It worked... and the results were almost unbelievable. We rigged the siphon tube with a rigid stick so it could be moved around along the bottom surfaces of the tank. After draining the entire 5 gallon contents out, we had caught three shop-towels full of these brown varnish flakes. It became obvious that this stuff was collecting around the finger strainer but was not passing through in normal operation. We poured in another 5 gallons of filtered avgas and repeated the process twice more and caught even more junk. These pictures show the results.
I am so glad to have found this an corrected it before something bad happened. I recommend that everyone should check out their tanks especially if they have ever sat for a period of time with mogas. Don't assume the tank is clean just because you have a clean gascolator screen.
It is hard to describe the feelings of surprise, relief, and bewilderment yesterday when we found out what an awful mess has been lurking inside my main fuel tank. To me... this is enough to cause me to NEVER use mogas ever again in an airplane. I guess that its ok if you fly regularly, but here's what can happen if you let mogas stagnate and set in your fuel tanks. This discovery yesterday came as a surprise because we recently thoroughly cleaned and flushed out the fuel tank during annual inspection. Since the annual, I have flown exclusively with avgas for around 8 hours with no hint of a fuel contamination problem. And I check and drain the gascolator before each flight. There has not even been one speck drained out on any flight. Same went for yesterday's pre-flight. I might have continued with this major problem unknowingly had I not made a unusual decision yesterday.
I was about to make an hour-long flight and I was debating about whether to plan a stop for fuel. The fuel float indicator was showing maybe a little less than half (I was thinking maybe 5 or 6 gallons). So I asked Lon (my father in law) to borrow the dipstick he has for his '39 tcraft. (This was the unusual decision.) It is a wood stick with a notch at every 2 gallon increment. So I dropped it down to the bottom of the tank to check the quantity. As the stick contacted the tank bottom, there was a distinct feeling that there was something else in the tank besides fuel. It felt like a layer of salt or sand... maybe a half inch deep laying in the bottom. Needless to say, I decided not to fly.
Lon and Travis helped me figure out what to do. We decided to rig up a siphon tube and see if we could vacuum it out. It worked... and the results were almost unbelievable. We rigged the siphon tube with a rigid stick so it could be moved around along the bottom surfaces of the tank. After draining the entire 5 gallon contents out, we had caught three shop-towels full of these brown varnish flakes. It became obvious that this stuff was collecting around the finger strainer but was not passing through in normal operation. We poured in another 5 gallons of filtered avgas and repeated the process twice more and caught even more junk. These pictures show the results.
I am so glad to have found this an corrected it before something bad happened. I recommend that everyone should check out their tanks especially if they have ever sat for a period of time with mogas. Don't assume the tank is clean just because you have a clean gascolator screen.
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