Mercury 300R HD CMS Mechanical Maintance Manual

Operation

and

Maintenance

Manual

© 2018 Mercury Marine

300R HD CMS Mechanical

8M0140585 518 eng

eng

Welcome

You have selected one of the finest marine power packages available. It
incorporates numerous design features to ensure operating ease and durability.

With proper care and maintenance, you will enjoy using this product for many
boating seasons. To ensure maximum performance and carefree use, we ask
that you thoroughly read this manual.

The Operation and Maintenance Manual contains specific instructions for using
and maintaining your product. We suggest that this manual remain with the
product for ready reference whenever you are on the water.

Thank you for purchasing one of our products. We sincerely hope your boating
will be pleasant!

Mercury Marine, Fond du Lac, Wisconsin, U.S.A.

Name / function:

John Pfeifer, President,
Mercury Marine

Read This Manual Thoroughly

IMPORTANT: If you do not understand any portion of this manual, contact your
dealer. Your dealer can also provide a demonstration of actual starting and
operating procedures.

Notice

Throughout this publication, and on your power package, warnings, cautions,

and notices, accompanied by the International Hazard Symbol

!

, may be
used to alert the installer and user to special instructions concerning a
particular service or operation that may be hazardous if performed incorrectly
or carelessly. Observe them carefully.

These safety alerts alone cannot eliminate the hazards that they signal. Strict
compliance with these special instructions while performing the service, plus
common sense operation, are major accident prevention measures.

!

WARNING

Indicates a hazardous situation which, if not avoided, could result in death or
serious injury.

!

CAUTION

Indicates a hazardous situation which, if not avoided, could result in minor or
moderate injury.

eng i

NOTICE

Indicates a situation which, if not avoided, could result in engine or major
component failure.

IMPORTANT: Identifies information essential to the successful completion of
the task.

NOTE: Indicates information that helps in the understanding of a particular step
or action.

IMPORTANT: The operator (driver) is responsible for the correct and safe
operation of the boat, the equipment aboard, and the safety of all occupants
aboard. We strongly recommend that the operator read this Operation and
Maintenance Manual and thoroughly understand the operational instructions for
the power package and all related accessories before the boat is used.

California Proposition 65

WARNING: This product can expose you to chemicals including
gasoline engine exhaust, which is known to the State of
California to cause cancer and birth defects or other
reproductive harm. For more information go to

www.P65Warnings.ca.gov.

The serial numbers are the manufacturer’s keys to numerous engineering
details that apply to your Mercury Marine power package. When contacting
Mercury Marine about service, always specify model and serial numbers.

Descriptions and specifications contained herein were in effect at the time this
was approved for printing. Mercury Marine, whose policies are based on
continuous improvement, reserves the right to discontinue models at any time
or to change specifications or designs without notice and without incurring
obligation.

Warranty Message

The product you have purchased comes with a limited warranty from Mercury
Marine; the terms of the warranty are set forth in the Warranty Manual included
with the product. The Warranty Manual contains a description of what is
covered, what is not covered, the duration of coverage, how to best obtain
warranty coverage, important disclaimers and limitations of damages, and
other related information. Please review this important information.

Mercury Marine products are designed and manufactured to comply with our
own high quality standards, applicable industry standards and regulations, as
well as certain emissions regulations. At Mercury Marine every engine is
operated and tested before it is boxed for shipment to make sure that the
product is ready for use. In addition, certain Mercury Marine products are
tested in a controlled and monitored environment, for up to 10 hours of engine
run time, in order to verify and make a record of compliance with applicable
standards and regulations. All Mercury Marine product, sold as new, receives
the applicable limited warranty coverage, whether the engine participated in
one of the test programs described above or not.

ii eng

Copyright and Trademark Information

© MERCURY MARINE. All rights reserved. Reproduction in whole or in
part without permission is prohibited.

Alpha, Axius, Bravo One, Bravo Two, Bravo Three, GO BOLDLY., Circle M with
Waves Logo, K‑planes, Mariner, MerCathode, MerCruiser, Mercury, Mercury
with Waves Logo, Mercury Marine, Mercury Precision Parts, Mercury
Propellers, Mercury Racing, MotorGuide, OptiMax, Quicksilver, SeaCore,
Skyhook, SmartCraft, Sport‑Jet, Verado, VesselView, Zero Effort, Zeus, #1 On
the Water and We're Driven to Win are registered trademarks of Brunswick
Corporation. Pro XS is a trademark of Brunswick Corporation. Mercury Product
Protection is a registered service mark of Brunswick Corporation.

Identification Records

Please record the following applicable information:

Outboard

Engine Model and Horsepower

Engine Serial Number

Gear Ratio

Propeller Number Pitch Diameter

Watercraft Identification Number (WIN) or Hull
Identification Number (HIN)

Purchase Date

Boat Manufacturer Boat Model Length

Exhaust Gas Emissions Certification Number (Europe Only)

eng iii

eng iv

General Information

Boater's Responsibilities..................................................................................... 1

Before Operating Your Outboard........................................................................ 1

Boat Horsepower Capacity................................................................................. 1

High‑Speed and High‑Performance Boat Operation.......................................... 2

Propeller Selection..............................................................................................2

Outboard Remote Control Models ..................................................................... 4

Lanyard Stop Switch........................................................................................... 5

Protecting People in the Water........................................................................... 7

Passenger Safety Message ‑ Pontoon Boats and Deck Boats...........................8

Wave and Wake Jumping................................................................................... 9

Impact with Underwater Hazards......................................................................10

Exhaust Emissions........................................................................................... 11

Selecting Accessories for Your Outboard......................................................... 13

Safe Boating Recommendations...................................................................... 13

Recording Serial Number................................................................................. 16

Specifications—300R HD................................................................................. 17

Component Identification.................................................................................. 19

Gearcase Identification..................................................................................... 20

Transporting

Trailering Boat/Outboard.................................................................................. 21

Fuel and Oil

Fuel Requirements........................................................................................... 22

Fuel Additives................................................................................................... 23

Low Permeation Fuel Hose Requirement ........................................................ 23

Fuel Demand Valve (FDV) Requirement.......................................................... 23

Engine Oil Recommendations—Race (R) Models............................................ 24

Checking and Adding Engine Oil...................................................................... 24

Features and Controls

Adaptive Speed Control.................................................................................... 28

Remote Control Features................................................................................. 28

Warning System............................................................................................... 28

Power Trim and Tilt...........................................................................................31

eng v

Operation

Important Daily Inspection Before Each Use ................................................... 36

Prestarting Check List.......................................................................................36

Operating in Freezing Temperatures................................................................ 36

Operating in Saltwater or Polluted Water......................................................... 37

Operating at High Elevations............................................................................ 37

Effects of Elevation and Weather on Performance........................................... 37

Setting Trim Angle while Running Engine at Idle Speed.................................. 38

Engine Break‑in Procedure...............................................................................39

Fuel Supply Module Priming Procedure........................................................... 39

Starting the Engine........................................................................................... 41

Gear Shifting..................................................................................................... 44

Stopping the Engine......................................................................................... 45

Maintenance

Cleaning Care Recommendations.................................................................... 46

EPA Emissions Regulations............................................................................. 48

Inspection and Maintenance Schedule............................................................. 49

300R HD Models Maintenance Schedule Decal............................................... 51

Flushing the Cooling System............................................................................ 52

Top Cowl Removal and Installation.................................................................. 52

Battery Inspection ............................................................................................ 54

Battery Cables and Clean Power Harness....................................................... 55

Fuel System...................................................................................................... 57

Corrosion Control Anode.................................................................................. 59

Propeller Replacement—31.75 mm (1‑1/4 in.) Diameter Propeller Shaft......... 60

Spark Plug Inspection and Replacement..........................................................61

Fuses................................................................................................................ 64

Alternator Drive Belt .........................................................................................66

Lubrication Points............................................................................................. 66

Trim Thrust Guide Wear Pad............................................................................ 68

Checking Power Trim Fluid (Single‑Ram Trim)................................................ 69

Checking Hydraulic Steering Fluid....................................................................70

Checking Power Steering Fluid........................................................................ 70

Changing Engine Oil and Filter......................................................................... 71

Checking Engine Oil Level................................................................................76

Exhaust Water Strainer Inspection................................................................... 77

Gearcase Lubricant.......................................................................................... 78

vi eng

Storage

Storage Preparation..........................................................................................81

Protecting External Outboard Components...................................................... 81

Protecting Internal Engine Components........................................................... 82

Gearcase.......................................................................................................... 82

Positioning Outboard for Storage..................................................................... 82

Battery Storage................................................................................................. 82

Troubleshooting

Starter Motor Will Not Crank the Engine........................................................... 83

Engine Will Not Start.........................................................................................83

Engine Runs Erratically.................................................................................... 83

Performance Loss.............................................................................................84

Battery Will Not Hold Charge............................................................................ 84

Owner Service Assistance

Service Assistance........................................................................................... 85

Ordering Literature............................................................................................87

Maintenance Log

Maintenance Log.............................................................................................. 89

eng vii

eng viii

Boater's Responsibilities

The operator (driver) is responsible for the correct and safe operation of the
boat and the safety of its occupants and general public. It is strongly
recommended that each operator read and understand this entire manual
before operating the outboard.

Be sure that at least one additional person onboard is instructed in the basics
of starting and operating the outboard and boat handling in case the driver is
unable to operate the boat.

Before Operating Your Outboard

Read this manual carefully. Learn how to operate your outboard properly. If you
have any questions, contact your dealer.

Safety and operating information that is practiced, along with using good
common sense, can help prevent personal injury and product damage.

This manual as well as safety labels posted on the outboard use the following
safety alerts to draw your attention to special safety instructions that should be
followed.

!

WARNING

Indicates a hazardous situation which, if not avoided, could result in death or
serious injury.

!

CAUTION

Indicates a hazardous situation which, if not avoided, could result in minor or
moderate injury.

NOTICE

Indicates a situation which, if not avoided, could result in engine or major
component failure.

Boat Horsepower Capacity

!

WARNING

Exceeding the boat's maximum horsepower rating can cause serious injury
or death. Overpowering the boat can affect boat control and flotation
characteristics or break the transom. Do not install an engine that exceeds
the boat's maximum power rating.

GENERAL INFORMATION

eng 1

Do not overpower or overload your boat. Most boats will carry a required
capacity plate indicating the maximum acceptable power and load as
determined by the manufacturer following certain federal guidelines. If in doubt,
contact your dealer or the boat manufacturer.

U.S. COAST GUARD CAP ACITY

MAXIMUM HORSEPOWER XXX

MAXIMUM PERSON
CAPACITY (POUNDS)

XXX

MAXIMUM WEIGHT
CAPACITY XXX

26777

High‑Speed and High‑Performance Boat Operation

If your outboard is to be used on a high‑speed or high‑performance boat with
which you are unfamiliar, we recommend that you do not operate it at its high
speed capability without first requesting an initial orientation and familiarization
demonstration ride with your dealer or an operator experienced with your boat/
outboard combination. For additional information, obtain a copy of our
Hi‑Performance Boat Operation booklet from your dealer, distributor, or
Mercury Marine.

Propeller Selection

The propeller on your outboard is one of the most important components in the
propulsion system. An improper propeller choice can significantly affect the
performance of your boat and could result in damage to the outboard engine.

When choosing a propeller, a full selection of aluminum and stainless steel
propellers specifically designed for your outboard are available through
Mercury Marine. To view the entire product offering and find the correct
propeller that is best suited for your application, visit
www.mercmarinepropellers.com or see your local authorized Mercury dealer.

SELECTING THE CORRECT PROPELLER

An accurate tachometer for measuring engine speed is important in choosing
the correct propeller.

Choose a propeller for your boating application that will allow the engine to
operate within the specified full throttle operating range. When operating the
boat at full throttle under normal load conditions, the engine RPM should be in
the upper half of the recommended full throttle RPM range. Refer to
Specifications. If engine RPM is above that range, select a propeller of
increased pitch in order to reduce engine RPM. If engine RPM is below the
recommended range, select a propeller of reduced pitch to increase engine
RPM.

GENERAL INFORMATION

2 eng

IMPORTANT: To ensure proper fit, and performance, Mercury Marine
recommends the use of Mercury or Quicksilver branded propellers and
mounting hardware.

Propellers are designated by the diameter, pitch, number of blades, and
material. The diameter and pitch are stamped (cast) into the side or the end of
the propeller hub. The first number represents the diameter of the propeller and
the second number represents the pitch. For example, 14x19 represents a
propeller with a 14 inch diameter and 19 inches of pitch.

a - Diameter
b - Pitch ‑ Travel during one revolution

The following are some propeller basics that will help you determine the correct
propeller for your boating application.

Diameter ‑ The diameter is the distance across the imaginary circle that is
made when the propeller rotates. The correct diameter for each propeller has
been predetermined for the design of your outboard. However, when more than
one diameter is available for the same pitch, use a larger diameter for heavy
boat applications and a smaller diameter for lighter applications.

Pitch ‑ The pitch is the theoretical distance, in inches, that a propeller travels
forward during one revolution. Pitch can be thought of similar to gears in a car.
The lower the gear, the faster the car will accelerate, but with lower overall top
speed. Likewise, a lower pitch propeller will accelerate quickly, but top‑end
speed will be reduced. The higher the propeller pitch the faster the boat will
usually go; though typically slowing acceleration.

Determining the correct pitch size ‑ First, check the full throttle RPM under
normal load condition. If the full throttle RPM is within the recommended range,
select a replacement or upgrade propeller with the same pitch as the current
propeller.

• Adding 1 inch of pitch will reduce the full throttle RPM by 150 to 200

• Subtracting 1 inch of pitch will increase full throttle RPM by 150 to 200

a

b

22669

GENERAL INFORMATION

eng 3

• Upgrading from a 3‑blade propeller to a 4‑blade propeller will generally
decrease full throttle RPM by 50 to 100

IMPORTANT: Avoid damage to the engine. Never use a propeller that allows
the engine to exceed the recommended full throttle RPM range when under
normal full throttle operation.

PROPELLER MATERIAL

Most propellers manufactured by Mercury Marine are made from either
aluminum or stainless steel. Aluminum is suitable for general purpose use and
is standard equipment on many new boats. Stainless steel is over five times
more durable than aluminum and typically provides performance gains in
acceleration and top end speed due to design efficiencies. Stainless steel
propellers also come in a larger variety of sizes and styles that allow you to dial
in the ultimate performance for your boat.

3 BLADE VS. 4 BLADE

Available in many sizes of both aluminum and stainless, 3 and 4‑blade
propellers have unique performance characteristics. In general, 3‑blade
propellers offer good all around performance and higher top speed than
4‑blade propellers. However, 4‑blade propellers are usually faster to plane and
more efficient at cruising speeds, but lack the top end speed of a 3‑blade
propeller.

Outboard Remote Control Models

The remote control connected to your outboard must be equipped with a start
in neutral only protection device. This prevents the engine from starting when
the shift is actuated in any position other than neutral.

!

WARNING

Starting the engine with the drive in gear can cause serious injury or death.
Never operate a boat that does not have a neutral‑safety‑protection device.

N

58237

GENERAL INFORMATION

4 eng

Lanyard Stop Switch

The purpose of a lanyard stop switch is to turn off the engine when the operator
moves far enough away from the operator's position (as in accidental ejection
from the operator's position) to activate the switch. Tiller handle outboards and
some remote control units are equipped with a lanyard stop switch. A lanyard
stop switch can be installed as an accessory ‑ generally on the dashboard or
side adjacent to the operator's position.

A decal near the lanyard stop switch is a visual reminder for the operator to
attach the lanyard to their personal flotation device (PFD) or wrist.

The lanyard cord is usually 122–152 cm (4–5 feet) in length when stretched out,
with an element on one end made to be inserted into the switch and a clip on
the other end for attaching to the operator's PFD or wrist. The lanyard is coiled
to make its at‑rest condition as short as possible to minimize the likelihood of
lanyard entanglement with nearby objects. Its stretched‑out length is made to
minimize the likelihood of accidental activation should the operator choose to
move around in an area close to the normal operator's position. If it is desired
to have a shorter lanyard, wrap the lanyard around the operator's wrist or leg,
or tie a knot in the lanyard.

a - Lanyard cord clip
b - Lanyard decal
c - Lanyard stop switch

Read the following Safety Information before proceeding.

c

a

b

53910

OFF

RUN

ATTACH LANYARD

GENERAL INFORMATION

eng 5

Important Safety Information: The purpose of a lanyard stop switch is to stop
the engine when the operator moves far enough away from the operator's
position to activate the switch. This would occur if the operator accidentally falls
overboard or moves within the boat a sufficient distance from the operator's
position. Falling overboard and accidental ejections are more likely to occur in
certain types of boats such as low sided inflatables, bass boats, high
performance boats, and light, sensitive handling fishing boats operated by a
hand tiller. Falling overboard and accidental ejections are also likely to occur as
a result of poor operating practices such as sitting on the back of the seat or
gunwale at planing speeds, standing at planing speeds, sitting on elevated
fishing boat decks, operating at planing speeds in shallow or obstacle infested
waters, releasing your grip on a steering wheel or tiller handle that is pulling in
one direction, drinking alcohol or consuming drugs, or daring high speed boat
maneuvers.

While activation of the lanyard stop switch will stop the engine immediately, a
boat will continue to coast for some distance depending upon the velocity and
degree of any turn at shut down. However, the boat will not complete a full
circle. While the boat is coasting, it can cause injury to anyone in the boat's
path as seriously as the boat would when under power.

We strongly recommend that other occupants be instructed on proper starting
and operating procedures should they be required to operate the engine in an
emergency (if the operator is accidentally ejected).

!

WARNING

If the operator falls out of the boat, stop the engine immediately to reduce the
possibility of serious injury or death from being struck by the boat. Always
properly connect the operator to the stop switch using a lanyard.

!

WARNING

Avoid serious injury or death from deceleration forces resulting from
accidental or unintended stop switch activation. The boat operator should
never leave the operator's station without first disconnecting the stop switch
lanyard from the operator.

Accidental or unintended activation of the switch during normal operation is
also a possibility. This could cause any, or all, of the following potentially
hazardous situations:

• Occupants could be thrown forward due to unexpected loss of forward
motion ‑ a particular concern for passengers in the front of the boat who
could be ejected over the bow and possibly struck by the gearcase or
propeller.

• Loss of power and directional control in heavy seas, strong current, or
high winds.

• Loss of control when docking.

GENERAL INFORMATION

6 eng

KEEP THE LANYARD STOP SWITCH AND LANYARD CORD IN GOOD
OPERATING CONDITION

Before each use, check to ensure the lanyard stop switch works properly. Start
the engine and stop it by pulling the lanyard cord. If the engine does not stop,
have the switch repaired before operating the boat.

Before each use, visually inspect the lanyard cord to ensure it is in good
working condition and that there are no breaks, cuts, or wear to the cord.
Check that the clips on the ends of the cord are in good condition. Replace any
damaged or worn lanyard cords.

Protecting People in the Water

WHILE YOU ARE CRUISING

It is very difficult for a person standing or floating in the water to take quick
action to avoid a boat heading in his/her direction, even at slow speed.

21604

Always slow down and exercise extreme caution any time you are boating in an
area where there might be people in the water.

Whenever a boat is moving (coasting) and the outboard gear shift is in neutral
position, there is sufficient force by the water on the propeller to cause the
propeller to rotate. This neutral propeller rotation can cause serious injury.

WHILE THE BOAT IS STATIONARY

!

WARNING

A spinning propeller, a moving boat, or any solid device attached to the boat
can cause serious injury or death to swimmers. Stop the engine immediately
whenever anyone in the water is near your boat.

Shift the outboard into neutral and shut off the engine before allowing people to
swim or be in the water near your boat.

GENERAL INFORMATION

eng 7

Passenger Safety Message ‑ Pontoon Boats and Deck Boats

Whenever the boat is in motion, observe the location of all passengers. Do not
allow any passengers to stand or use seats other than those designated for
traveling faster than idle speed. A sudden reduction in boat speed, such as
plunging into a large wave or wake, a sudden throttle reduction, or a sharp
change of boat direction, could throw them over the front of the boat. Falling
over the front of the boat between the two pontoons will position them to be run
over by the outboard.

BOATS HAVING AN OPEN FRONT DECK

No one should ever be on the deck in front of the fence while the boat is in
motion. Keep all passengers behind the front fence or enclosure.

Persons on the front deck could easily be thrown overboard or persons
dangling their feet over the front edge could get their legs caught by a wave
and pulled into the water.

26782

!

WARNING

Sitting or standing in an area of the boat not designed for passengers at
speeds above idle can cause serious injury or death. Stay back from the front
end of deck boats or raised platforms and remain seated while the boat is in
motion.

BOATS WITH FRONT MOUNTED, RAISED PEDESTAL FISHING SEATS

Elevated fishing seats are not intended for use when the boat is traveling faster
than idle or trolling speed. Sit only in seats designated for traveling at faster
speeds.

GENERAL INFORMATION

8 eng

Any unexpected, sudden reduction in boat speed could result in the elevated
passenger falling over the front of the boat.

26783

Wave and Wake Jumping

Operating recreational boats over waves and wake is a natural part of boating.
However, when this activity is done with sufficient speed to force the boat hull
partially or completely out of the water, certain hazards arise, particularly when
the boat enters the water.

26784

The primary concern is the boat changing direction while in the midst of the
jump. In such case, the landing may cause the boat to veer violently in a new
direction. Such a sharp change in direction can cause occupants to be thrown
out of their seats, or out of the boat.

!

WARNING

Wave or wake jumping can cause serious injury or death from occupants
being thrown within or out of the boat. Avoid wave or wake jumping whenever
possible.

There is another less common hazardous result from allowing your boat to
launch off a wave or wake. If the bow of your boat pitches down far enough
while airborne, upon water contact it may penetrate under the water surface
and submarine for an instant. This will bring the boat to a nearly instantaneous
stop and can send the occupants flying forward. The boat may also steer
sharply to one side.

GENERAL INFORMATION

eng 9

Impact with Underwater Hazards

Your outboard is equipped with a hydraulic trim and tilt system that also
contains a shock absorbing feature. This feature helps the outboard withstand
damage in the case of impact with an underwater object at low to moderate
speeds. At higher speeds, the force of the impact may exceed the system’s
ability to absorb the energy of the impact and cause serious product damage.

No impact protection exists while in reverse. Use extreme caution when
operating in reverse to avoid striking underwater objects.

Reduce speed and proceed with caution whenever you drive a boat in shallow
water areas or in areas where you suspect underwater obstacles may exist that
could be struck by the outboard or the boat bottom. The most significant

action you can take to help reduce injury or impact damage from striking
a floating or underwater object is to control the boat speed. Under these
conditions, boat speed should be kept to the minimum planing speed,
typically 24 to 40 km/h (15 to 25 mph).

26785

!

WARNING

Avoid serious injury or death from all or part of an outboard or drive unit
coming into the boat after striking a floating or underwater object. When
operating in waters where objects may be at the surface or just under the
surface of the water, reduce your speed and keep a vigilant lookout.

Examples of objects that can cause engine damage are dredging pipes,
bridge supports, wing dams, trees, stumps, and rocks.

Striking a floating or underwater object could result in any of an infinite number
of situations. Some of these situations could yield the following:

• Part of the outboard or the entire outboard could break loose and fly into
the boat.

• The boat could move suddenly in a new direction. A sharp change in
direction can cause occupants to be thrown out of their seats or out of the
boat.

• The boat's speed could rapidly reduce. This will cause occupants to be
thrown forward or even out of the boat.

GENERAL INFORMATION

10 eng

• The outboard or boat could sustain impact damage.

After striking a submerged object, stop the engine as soon as possible and
inspect it for any broken or loose parts. If damage is present or suspected, the
outboard should be taken to an authorized dealer for a thorough inspection and
necessary repair.

The boat should also be checked for any hull fractures, transom fractures, or
water leaks. If water leaks are discovered after an impact, immediately activate
the bilge pump.

Operating a damaged outboard could cause additional damage to other parts
of the outboard or could affect control of the boat. If continued running is
necessary, do so at greatly reduced speeds.

!

WARNING

Operating a boat or engine with impact damage can result in product
damage, serious injury, or death. If the vessel experiences any form of
impact, have an authorized Mercury Marine dealer inspect and repair the
vessel or power package.

Exhaust Emissions

BE ALERT TO CARBON MONOXIDE POISONING

Carbon monoxide (CO) is a deadly gas that is present in the exhaust fumes of
all internal combustion engines, including the engines that propel boats, and
the generators that power boat accessories. By itself, CO is odorless, colorless,
and tasteless, but if you can smell or taste engine exhaust, you are inhaling
CO.

Early symptoms of carbon monoxide poisoning, which are similar to the
symptoms of seasickness and intoxication, include headache, dizziness,
drowsiness, and nausea.

!

WARNING

Inhaling engine exhaust gases can result in carbon monoxide poisoning,
which can lead to unconsciousness, brain damage, or death. Avoid exposure
to carbon monoxide.

Stay clear from exhaust areas when engine is running. Keep the boat
well‑ventilated while at rest or underway.

GENERAL INFORMATION

eng 11

STAY CLEAR OF EXHAUST AREAS

41127

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

co

Engine exhaust gases contain harmful carbon monoxide. Avoid areas of
concentrated engine exhaust gases. When engines are running, keep
swimmers away from the boat, and do not sit, lie, or stand on swim platforms or
boarding ladders. While underway, do not allow passengers to be positioned
immediately behind the boat (platform dragging, teak/body surfing). This
dangerous practice not only places a person in an area of high engine exhaust
concentration, but also subjects them to the possibility of injury from the boat
propeller.

GOOD VENTILATION

Ventilate the passenger area, open side curtains or forward hatches to remove
fumes.

Example of desired air flow through the boat:

POOR VENTILATION

Under certain running and/or wind conditions, permanently enclosed or canvas
enclosed cabins or cockpits with insufficient ventilation may draw in carbon
monoxide. Install one or more carbon monoxide detectors in your boat.

Although the occurrence is rare, on a very calm day, swimmers and
passengers in an open area of a stationary boat that contains, or is near, a
running engine may be exposed to a hazardous level of carbon monoxide.

GENERAL INFORMATION

12 eng

1. Examples of poor ventilation while the boat is stationary:

a - Operating the engine when the boat is moored in a confined space
b - Mooring close to another boat that has its engine operating

2. Examples of poor ventilation while the boat is moving:

a - Operating the boat with the trim angle of the bow too high
b - Operating the boat with no forward hatches open (station wagon effect)

Selecting Accessories for Your Outboard

Genuine Mercury Precision or Quicksilver Accessories have been specifically
designed and tested for your outboard. These accessories are available from
Mercury Marine dealers.

IMPORTANT: Check with your dealer before installing accessories. The misuse
of approved accessories or the use of nonapproved accessories can damage
the product.

Some accessories not manufactured or sold by Mercury Marine are not
designed to be safely used with your power package and may void warranty.
Acquire and read the installation and operation manuals for each selected
accessory.

Safe Boating Recommendations

To safely enjoy the waterways, familiarize yourself with local and all other
governmental boating regulations and restrictions and consider the following
suggestions.

Know and obey all nautical rules and laws of the waterways.

21626

a

b

a

b

21628

GENERAL INFORMATION

eng 13

• We recommend that all powerboat operators complete a boating safety
course. In the U.S., the U.S. Coast Guard Auxiliary, the Power Squadron,
the Red Cross, and your state or provincial boating law enforcement
agency provide courses. For more information in the U.S., call the Boat
U.S. Foundation at 1‑800‑336‑BOAT (2628).

Perform safety checks and required maintenance.

• Follow a regular schedule and ensure that all repairs are properly made.

Check safety equipment onboard.

• Here are some suggestions of the types of safety equipment to carry
when boating:

Approved fire extinguishers

Signal devices: flashlight, rockets or flares, flag, and whistle or horn

Tools necessary for minor repairs

Anchor and extra anchor line

Manual bilge pump and extra drain plugs

Drinking water

Radio

Paddle or oar

Spare propeller, thrust hubs, and an appropriate wrench

First aid kit and instructions

Waterproof storage containers

Spare operating equipment, batteries, bulbs, and fuses

Compass and map or chart of the area

Personal flotation device (one per person onboard)

Watch for signs of weather change and avoid foul weather and rough‑sea
boating.

Tell someone where you are going and when you expect to return.

Passenger boarding.

• Stop the engine whenever passengers are boarding, unloading, or are
near the back (stern) of the boat. Shifting the drive unit into neutral is not
sufficient.

Use personal flotation devices.

• Federal law requires that there be a U.S. Coast Guard‑approved life
jacket (personal flotation device), correctly sized and readily accessible
for every person onboard, plus a throwable cushion or ring. We strongly
advise that everyone wear a life jacket at all times while in the boat.

Prepare other boat operators.

GENERAL INFORMATION

14 eng

• Instruct at least one person onboard in the basics of starting and
operating the engine and boat handling in case the driver becomes
disabled or falls overboard.

Do not overload your boat.

• Most boats are rated and certified for maximum load (weight) capacities
(refer to your boat's capacity plate). Know your boat's operating and
loading limitations. Know if your boat will float if it is full of water. When in
doubt, contact your authorized Mercury Marine dealer or the boat
manufacturer.

Ensure that everyone in the boat is properly seated.

• Do not allow anyone to sit or ride on any part of the boat that was not
intended for such use. This includes the backs of seats, gunwales,
transom, bow, decks, raised fishing seats, and any rotating fishing seat.
Passengers should not sit or ride anywhere that sudden unexpected
acceleration, sudden stopping, unexpected loss of boat control, or sudden
boat movement could cause a person to be thrown overboard or into the
boat. Ensure that all passengers have a proper seat and are in it before
any boat movement.

Never operate a boat while under the influence of alcohol or drugs. It is
the law.

• Alcohol or drugs can impair your judgment and greatly reduce your ability
to react quickly.

Know your boating area and avoid hazardous locations.

Be alert.

• The operator of the boat is responsible by law to maintain a proper
lookout by sight and hearing. The operator must have an unobstructed
view particularly to the front. No passengers, load, or fishing seats should
block the operator's view when the boat is above idle or planing transition
speed. Watch out for others, the water, and your wake.

Never drive your boat directly behind a water‑skier.

• Your boat traveling at 40 km/h (25 mph) will overtake a fallen skier who is
61 m (200 ft) in front of you in five seconds.

Watch fallen skiers.

• When using your boat for waterskiing or similar activities, always keep a
fallen or down skier on the operator's side of the boat while returning to
attend to the skier. The operator should always have the down skier in
sight and never back up to the skier or anyone in the water.

Report accidents.

GENERAL INFORMATION

eng 15

• Boat operators are required by law to file a boating accident report with
their state boating law enforcement agency when their boat is involved in
certain boating accidents. A boating accident must be reported if 1) there
is loss of life or probable loss of life, 2) there is personal injury requiring
medical treatment beyond first aid, 3) there is damage to boats or other
property where the damage value exceeds $500.00, or 4) there is
complete loss of the boat. Seek further assistance from local law
enforcement.

Recording Serial Number

It is important to record this number for future reference. The serial number is
located on the outboard, as shown.

a - Model designation
b - Serial number
c - Certified Europe insignia (as applicable)

a

XXXXXXXXX

XXXXXXXX

XXXX

c

b

66301

GENERAL INFORMATION

16 eng

Specifications—300R HD

300R HD MODELS

Attribute 300R HD
Horsepower 300
Kilowatts 221
Full throttle RPM range 5800–6400
Idle RPM in neutral gear* 600
Idle charge compensation** 600–725
Troll control RPM limit 550–1000
Number of cylinders 8

Displacement

4.6 Liter

4,576 cc (279.2 cid)
Cylinder bore 92 mm (3.62 in.)
Stroke 86 mm (3.38 in.)
Spark plug NGK LKAR7C‑9
Spark plug gap 0.9 mm (0.035 in.)
Spark plug hex size 14 mm
Sport Master ratio 1.75:1
137 mm (5.4 in.) ratio 1.75:1

Gearcase
capacity

Sport Master
RH, LH

620 mL (21.0 fl oz)

137 mm (5.4
in.) RH

720 mL (24.4 fl oz)

137 mm (5.4
in.) LH

680 mL (23.0 fl oz)

Recommended gasoline

Refer to Fuel and Oil

Recommended oil

Refer to Fuel and Oil

Engine oil capacity with oil
filter replacement

6.6 Liter (7.0 US qt)

Required battery type 12‑volt absorbed glass mat (AGM) battery

Battery
type***

USA (SAE)

800 minimum marine cranking amps (MCA)

with a minimum reserve capacity of 135

RC25 rating

International
(EN)

975 minimum cold cranking amps (CCA) with

a minimum 65 amp hour (Ah)

GENERAL INFORMATION

eng 17

*Engine at normal operation temperature.
**The idle charge compensation may automatically increase the engine speed

up to 725 RPM to compensate for a low battery charge condition. The
increased idle RPM will charge the battery at a higher rate. Activating troll
control (optional accessory) will override the idle charge compensation
feature.

***Battery manufacturers may rate and test their batteries to different
standards. MCA, CCA, Ah, and reserve capacity (RC) are the ratings
recognized by Mercury Marine. Manufacturers that use standards different
than these, such as equivalent MCA, do not meet Mercury Marine battery
requirements.

GENERAL INFORMATION

18 eng

Component Identification

a - Service access door
b - Top cowl
c - Engine flush
d - Auxiliary tilt switch
e - Cooling water intake holes
f - External steering bracket (dealer installed option or factory installation

available)

g - Water pump indicator hole
h - Engine oil drain
i - Exhaust relief

a

b

c

d

f

g

h

i

e

66302

GENERAL INFORMATION

eng 19

Gearcase Identification

Diameter

or Type

Identification

Features

Illustration

137 mm
(5.4 in.)

Water intake—

eight per side,

four torpedo low

water

L

L

64308

Left‑hand rotation

gearcase—LL
stamped on the
end of propeller

shaft

Sport
Master

Water intake—

three torpedo low

water

64532

L

L

Left‑hand rotation

gearcase—LL
stamped on the
end of propeller

shaft

GENERAL INFORMATION

20 eng