Mercury Optimax Models 135, 150, Direct Fuel Injection., Page 12Get this manual
MAINTENANCE
Flushing Engine
Flushing Cooling System Using Cowl Flush Plug
Flush the internal water passages of the outboard with fresh water after each use in salt, polluted or muddy waterThis will help prevent buildup of deposits from clogging the internal water passages
NOTE: Engine can be stopped or running at idle speed when flushing the cooling systemDo not flush engine using water system that exceeds 45 psi1Remove the plug from fitting in the bottom cowl