Found this , may be interesting:
Effective October, 2010, Mercury has "officially" announced a change in it's oil recommendation for the entire line of ProXS Engines.
Due to a better additive package (that helps to decrease carbon buildup), OPTIMAX/DFI oil is now recommended for ALL ProXS Engines.
Premium Plus still meets the requirement... and is still safe to use, but Optimax/DFI oil is now considered the "first choice" oil. IMHO... the Optimax oil would be of benefit to those that run for extended times at lower RPM's (such as long no-wake zones, extensive side imaging, etc.). Another reason that has contributed to carbon buildup is the introduction of Ethanol into fuel supplies, and this change may help to combat this buildup, ESPECIALLY when combined with regular use of Quickleen.
The following is from the official announcement (courtesy: Mercury Marine):
"Effective October 2010, Mercury OptiMax / DFI or Quicksilver DFI 2-Cycle engine oil is the recommended oil for all OptiMax models - including Pro XS. (The previous recommendation stated the use of Mercury Premium Plus 2-Cycle Outboard Oil in ProXS models and OptiMax oil in non-ProXS models.)
OptiMax / DFI oil is a superior oil when compared to the Premium Plus oil. While both products are high quality 2-cycle engine oils suitable for use in OptiMax engines, the OptiMax / DFI oil contains a higher percentage of additives that reduce carbon deposit formation.
Over time, under normal operating conditions, carbon deposits accumulate in the power cylinder (piston, cylinder head, liners). In most cases the carbon deposits do not create a problem, but carbon deposits that form on the piston - particularly behind the piston rings and piston skirts - can reduce engine life and performance.
OptiMax / DFI oil is specially formulated to prevent the carbon deposits from forming. It also does a better job of reducing existing carbon deposits than the Premium Plus oil. Going forward, the Operation, Maintenance and Warranty manuals for OptiMax outboards will recommend Mercury OptiMax / DFI or Quicksilver DFI 2-Cycle engine oil to help maximize engine life and performance."
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