I respectfully disagree.
Here is why:
"Appearance" as in 'seams to me' - - is just a
corollary to the "hope is a method [not]
" frame of mind
that is really not appropriate for aircraft related activities.
I have instrumented up plugs and flown
them.
These plugs covered several heat ranges. They
all ended up looking the same to random observers - - and their critical
core temperatures covered a sufficiently wide range to qualify as "good" or
"marginal".
Regards, George
Gary! You made an excellent point about looking at the
plug to determine if it is the right heat range. I remember the illustrations in
my auto manuals that showed the pictures of plugs that were too cold, too hot,
or just right. 'Seems to me that is some of the best instrumentation you could
have of the correct heat range of the plug, bar none. Too hot and the insulator
was blistered; too cold and it was covered with eposits; just right and it had a
nice, light tan coating on the insulator! BTW, Lycoming is making available
cylinders drilled and tapped for automotive plugs. Maybe somebody should warn
them. Or maybe they have done some testing with EI systems and found them
acceptable; they have!