Mercury 305 CID, Service Manual, Page: 29 / 967

1B-12 - MAINTENANCE 90-823225--1 1096
All Models
20-Hour Break-In Period
IMPORTANT: The first 20 hours of operation is
the engine break-in period. Correct break-in is
essential to obtain minimum oil consumption
and maximum engine performance. During this
break-in period, the following rules must be ob-
served:
•
Do not operate below 1500 RPM for extended pe-
riods of time for first 10 hours. Shift into gear as
soon as possible after starting and advance
throttle above 1500 RPM if conditions permit safe
operation.
•
Do not operate at one speed consistently for ex-
tended periods.
•
Do not exceed 3/4 throttle during first 10 hours.
During next 10 hours, occasional operation at full
throttle is permissible (5 minutes at a time maxi-
mum).
•
Avoid full throttle acceleration from idle speed.
•
Do not operate at full throttle until engine reaches
normal operating temperature.
•
Frequently check crankcase oil level. Add oil if
needed. It is normal for oil consumption to be high
during break-in period.
•
After 20-hour break-in period, drain crankcase oil
and replace oil filter (see “Maintenance”). Fill
crankcase with correct oil (see “Specifications”).
After Break-In Period
•
Use a propeller that allows the engine to operate
at or near the top of the maximum RPM range (see
Specifications section) when at full throttle with a
normal boat load.
•
Operation at 3/4 throttle setting or lower is recom-
mended. Refrain from prolonged operation at
maximum (full throttle) RPM.
•
Deterioration of elastomer and plastic parts.
•
Fuel permeation through flexible fuel lines.
•
Wear and damage of internal engine parts.
•
Starting and operating difficulties.
Some of these adverse effects are due to the tenden-
cy of gasolines containing alcohol to absorb moisture
from the air, resulting in a phase of water and alcohol
separating from the gasoline in the fuel tank.
Fuel, Oil, Fluid, and Coolant
Specifications
Fuel
! CAUTION
Use of improper gasoline can damage the engine
seriously. Engine damage that results from use
of improper gasoline is considered misuse of the
engine and is not covered under MerCruiser War-
ranty.
USA and Canada
Fuel having a posted pump Octane Rating of 87(R +
M)/2 minimum. Premium gasoline [92 (R + M)/2] is
also acceptable. DO NOT use leaded gasoline.
Outside USA and Canada
Fuel having a posted pump Octane Rating of 92 RON
minimum. Premium gasoline (98 RON) is also
acceptance. If unleaded is not available, use a major
brand of leaded gasoline.
Gasolines containing alcohol, either methyl alcohol
(methanol) or ethyl alcohol (ethanol) may cause
increased:
•
Corrosion of metal parts.
•
Deterioration of elastomer and plastic parts.
•
Fuel permeation through flexible fuel lines.
•
Wear and damage of internal engine parts.
•
Starting and operating difficulties.
Some of these adverse effects are due to the
tendency of gasolines containing alcohol to absorb
moisture from the air, resulting in a phase of water
and alcohol separating from the gasoline in the fuel
tank.
The adverse effects of alcohol are more severe with
methyl alcohol (methanol) and are worse with in-
creasing alcohol content.