Caution - InterAv "Spike Guard" Capacitor

snip
: Inter-Av claims very few failures of this capacitor... but I'm wondering.
: Unless you physically shake the can, you won't know if the electrolyte
: evaporated. (That means you have to take it out of the Adel clamp... which is
: probably never done during inspection.) While a firewall isn't as severe a
: heat location as a front baffle, our firewall still gets fairly hot after a few
: hours of flying. Don't know if the electrolyte drying out is a function of
: boiling point or long term evaporation. Sounds like further investigation is
: warranted.

The cap should not rattle even if the electrolyte dries out. The cap is not
constructed like a flooded cell battery. It's made of two pieces of aluminum
foil with a very thin, porous, paperlike material sandwiched between them.
This porous material is soaked in electrolyte like a damp cloth. This whole
mess is then rolled up like a set of blueprints so as to increase the surface
area (equation of capacitance is Capacitance = Area * Dielectric Constant).
If the electrolyte evaporates, the capacitance decreases. If the electrolyte
evaporates quickly, the capacitor can will bulge out, explode, or "vent"
the overpressure. There is probably a small vent opening on the top of
your capacitor next to the screw terminals. If this is not popped open the
electrolyte is probably still contained in the cap.

It sounds to me like your capacitor has failed due to mechanical vibration.
This is the only way I can think of that would leave the guts of an
electrolytic cap rattling.

--
Aaron Coolidge (N9376J)
"100% of the world is covered by air. Use it all." - Citation ad