Marine engine break-in procedure for 4-cycle MerCruiser Engines from Mercury Marine. Follow the instructions below on how to break in a new engine.

First 20 Hours

  • Do NOT operate the engine below 1500 rpm for extended periods of time. Shift into gear as soon as possible after starting the engine. Advance the throttle above 1500 rpm if conditions permit safe operation.
  • Do NOT operate at one continuous speed for extended periods of time. Vary the throttle position every ten to fifteen minutes.
  • Do NOT exceed ¾ throttle during the first 10 hours of operation. During the next 10 hours you may occasionally operate at full throttle for no more than 5 minutes at a time.
  • Do NOT operate at full throttle until the engine reaches normal operating temperatures.
  • Avoid full throttle acceleration from an IDLE speed.


After first 20 Hours

  • Install and maintain the correct propeller for the application. Make sure the prop allows the engine to operate at (or near) the top of its specified Wide-Open-Throttle rpm range. Refer to the Owner’s Manual, or consult with your marine dealer to determine the correct prop for the application.
  • Refrain from extended periods of Wide-Open-Throttle. Mercury Marine recommends cruising at ¾ throttle or below for longer term operation.
  • Change the oil and filter regularly. Refer to Specifications and Maintenance section of the MerCruiser Owners Guide for recommendations.