I have noticed that if I leave my plane sitting in the sun on a warm day, the fuel pumps will be much louder when I go to start it. I've come to realize that this sound is the pumps beginning to cavitate when the fuel in the tank is hot and more prone to vaporize at the pump inlet. This only happens with Mogas (typically winter blend) and never happens with Avgas. Now that I recognize it for what it is, I see it as a no-fly condition.
I have experimented with Avgas in one tank and Mogas in the other, and under the right conditions the difference in the sound of the fuel pumps when switching between the tanks is very telling. This obviously has implications for vapor lock, but it has also started me wondering if pump cavitation (without actual vapor lock) is contributing to early pump failures in some aircraft. I know in other mechanical systems pump cavitation can be very damaging.
