How to "READ"
your glow plug
OS and Turbo glow plugs go gray sooner
(easier) than McCoy plugs; this is not
necessarily bad. Actually when a new plug wire
just goes slightly gray after a 5 or 10 minute
hard run it means you are very close to an optimal
horsepower tune, but be careful the next step is
TOO LEAN!
Make a few hot laps then stop engine and pull
the plug to "read". General rules to reading a
plug are:
- Wire and surrounding bottom of plug wet
and new wire is shiny = rich side of optimum
power. About 85% of max performance.
- Wire and surrounding bottom of plug
starting to dry and wire starting to gray =
Very close to optimum power. About 95% of
max performance.
- Wire and surrounding bottom of plug dry,
wire totally gray but not distorted =
optimum power 100%
- Wire and surrounding bottom of plug dry,
wire distorted = slightly lean DANGER!
- Wire and surrounding bottom of plug dry,
wire broken and distorted or burnt up =
extremely lean possible engine damage!
Note: You can only "Read" your plug in a
nearly new state [Wire like new and shiny] A
gray plug can still operate well. But after it
has totally gone gray performance can start to
fall off. To test just put in a new plug and if
there is no difference in performance save the
gray one or put it back in. If your engine does
not feel or run right try a new plug before
making major tune changes.