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Ventilation
Ventilation is caused by surface air or exhaust gases that are introduced around the propeller resulting in propeller speed‑up and
a reduction in boat speed. Air bubbles strike the propeller blade and cause erosion of the blade surface. If allowed to continue,
eventual blade failure (breakage) will occur. Excessive ventilation is usually caused by:
•
Drive unit trimmed out too far
•
A missing propeller diffuser ring
•
A damaged propeller or gear housing, which allows exhaust gases to escape between propeller and gear housing
•
Drive unit installed too high on transom
Elevation and Climate
NOTE: Engines equipped with an Engine Control Module (ECM) reduce the effects of changes in elevation and climate by
automatically adjusting fuel flow for weather conditions and elevation. ECM controlled engines, however, do not compensate for
increased loading or hull conditions.
Elevation and climate changes affect the performance of your power package. Loss of performance can be caused by:
•
High elevations
•
High temperatures
•
Low barometric pressures
•
High humidity
For optimum engine performance under changing weather conditions and high elevation, use a propeller that allows the engine
to operate at rated RPM at wide open throttle (WOT) with a maximum boat load during your normal boating.
In most cases, the rated RPM at WOT can be achieved by changing to a lower pitch propeller.
Propeller Selection
Operating the engine with the wrong propeller installed can limit power, increase fuel consumption, overheat the engine, or
cause internal powerhead damage. Choose a propeller that allows the engine to operate at the specified wide open throttle
RPM.
The boat manufacturer and the selling dealer are responsible for equipping the power package with the correct propellers.
IMPORTANT: The engines covered in this manual are equipped with an ECM that limits engine RPM. Be sure that the propeller
being used does not allow the engine to run against the limiter, as a significant loss in performance will result.
NOTE: Use an accurate service tachometer to verify RPM.
Select a propeller that will allow the engine power package to operate at the rated engine RPM with a maximum load.
If full throttle operation is below the engine rated RPM, the propeller must be changed to prevent loss of performance and possible
engine damage. On the other hand, operating an engine above the rated engine RPM will cause higher than normal wear or
damage.
After initial propeller selection, the following common problems may require that the propeller be changed to a lower pitch:
•
Warmer weather and greater humidity cause an RPM loss (not as significant on these models).
•
Operating in a higher elevation causes an RPM loss (not as significant on these models).
•
Operating with a damaged propeller or dirty boat bottom causes an RPM loss.
•
Operating with increased load (additional passengers, pulling skiers).
For better acceleration, such as is needed for water skiing, use the next lower pitch propeller. Do not operate at full throttle when
using the lower pitch propeller but not pulling skiers.
Getting Started
Initial Break‑In Procedure
The following procedure is especially important on new diesel engines. This break‑in procedure allows the proper seating of the
pistons and rings, which greatly reduces the likelihood of problems.
IMPORTANT: Cummins MerCruiser Diesel recommends that the boat not be accelerated hard until this procedure has been
completed.
1.
See the appropriate Starting, Shifting, and Stopping section and start the engine.
2.
Operate the engine at a fast idle until it has reached normal operating temperature.
3.
Operate the engine in gear for 3 minutes at each of the following RPM: 1200 RPM, 2400 RPM and 3000 RPM.
90-8M0057081
MARCH 2011
eng
NOTICE
Section 3 - On the Water
Page 33
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