ENGINE MECHANICAL SERVICE MANUAL NUMBER 22
Page 3A-154 90-860074--1 FEBRUARY 2002
Engine 20-Hour Break-In Period
The first 20 hours of operation is the engine (new or rebuilt) break-in period. During this
period, it is extremely important that the engine is operated as outlined in the following.
1. Do NOT operate engine below 1500 rpm for extended periods of time during the first 10
hours. During this period, shift into gear as soon as possible after starting engine and
advance throttle so that rpm is above 1500 (provided that conditions permit safe opera-
tion at this speed).
2. Do NOT operate at any one constant speed for extended periods of time.
3. Do NOT exceed 75% of full throttle during the first 10 hours except during the Engine
Initial Break-In Procedure. During the next 10 hours, occasional operation at full throttle
(5 minutes at a time maximum) is permissible.
4. AVOID full throttle accelerations from stopped position.
5. Do NOT operate at full throttle until engine reaches normal operating temperature.
6. OBSERVE INSTRUMENTATION carefully. If an abnormal reading occurs, stop engine
immediately and determine cause.
7. FREQUENTLY CHECK crankcase oil level and add oil if necessary. It is normal for oil
consumption to be somewhat high during the break-in period.
8. AT END OF THE 20-HOUR BREAK-IN PERIOD, drain oil from crankcase and replace
oil and filter. Fill crankcase with correct grade and viscosity oil.
After Break-in Period
To help extend the life of your Mercury MerCruiser power package, the following
recommendations should be considered;
• Use a propeller that allows the engine to operate at or near the top of the maximum
rpm range when at full throttle with a normal boat load.
• Operation at 3/4 throttle setting or lower is recommended. Refrain from prolonged
operation at maximum full throttle rpm.
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