I may be beating a dead horse with all this discussion about spark plug difference but I'd sure like to understand why the slight discrepancies and why the change from one year to another. What does it all mean?
NGK, after conversation with them, revised their specs and sent me this info in an email:
(Here is the current up to date application listing for this engine:
MERCURY2006 225 hp 6-cyl. 2-Stroke 225 OptiMax IZFR5G .031
MERCURY2004-1996 225 hp 6-cyl. 2-Stroke 225 OptiMax PZFR5F-11 .040
So the 96-04 models use the platinum plug with the larger gap setting (.040”). Because both plugs have identical dimensions besides the gap they can be used interchangeably without a problem, just be sure they are all gapped the same. Hope this helps, thank you.)
The Merc opti manual says this:
0.8 mm (0.031 in.)
1.1 mm (0.043 in.)
So - why did Merc change from PZ gapped at (.040 NGK figure) (.043 Merc figure) to IZ gapped at .031 in 2005?
And - why does NGK say plugs can be used interchangeably as long as all are gapped at .040? .040 is a good bit away from the Merc requirement of .031 for IZ.
Your knowledgeable comments appreciated.