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Mercruiser 4-Cycle Engine Break-In Procedure

Repair Time: More than 4 hours
Repair Difficulty: Medium
Mercruiser 4-Cycle Engine Break-In Procedure
Mercury Marine Outboard


  1. First 20 Hours:
  2. After First 20 Hours:

The first 20-hours of operation will have a dramatic affect relative to overall engine performance and expected engine life. Proper break-in practices reduce the potential for excessive oil consumption. It also helps to achieve better engine performance levels for a longer period of time.

First 20 Hours:

  1. DO NOT operate the engine below 1500 rpm for extended period$ pf time. Shift into gear as soon as possible after starting the engine. Advance the throttle above 1500rpm if conditions permit safe operation.

  2. DO NOT operate at one continuous speed for extended periods of time. Vary the throttle position every ten to fifteen minutes.

  3. DO NOT exceed 3/4 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 as a time.

  4. DO NOT operate at full throttle until the engine reaches normal operating temperatures.

  5. Avoid full throttle acceleration from an IDLE speed.

After First 20 Hours:

To help extend the engine life for a remanufactured MerCruiser engine, consider the following recommendations.

  1. 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.

  2. Refrain from extended periods of Wide-Open-Throttle. We recommend cruising at 3/4 throttle or below for longer term operation.

  3. Change the oil and filter regularly. Refer to the Specifications and Maintenance section of the MerCruiser Owners Guide for recommendations.

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