Mercury 300 - PRO MAX 3.0L User manual

300 - PRO MAX 3.0L
1999 Mercury Marine90Ć849233000 499
for your purchase of one of the finest outboards available.
You have made a sound investment in boating pleasure.
Your outboard has been manufactured by Mercury Rac-
ing, a unit of Mercury Marine, the world leader in marine
technology and outboard manufacturing since 1939.
These years of experience have been committed to the
goal of producing the finest quality products. This has led
to Mercury Racing’s reputation for strict quality control,
excellence, durability, lasting performance and being the
best at providing after-the-sale support.
Please read this manual carefully before operating your
outboard. This manual has been prepared to assist you
in the operation, safe use and care of your outboard.
All of us at Mercury Racing took pride in building your out-
board and wish you many years of happy and safe boat-
ing.
Again, thank you for your confidence in Mercury Marine.
Mercury Racing
N7480 County Road “UU”
Fond du Lac, WI 54935-9585

0

1
oa TABLE OF CONTENTS
General Information
Boater’s Responsibilities 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Before Operating Your Outboard 4. . . . . . . . . . . . . . . . . . . . . . .
Boat Horsepower Capacity 5. . . . . . . . . . . . . . . . . . . . . . . . . . . .
High-Speed And High-Performance Boat Operation 5. . . . . .
Lanyard Stop Switch 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Protecting People In The Water 8. . . . . . . . . . . . . . . . . . . . . . . .
Carbon Monoxide Risk 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wave And Wake Jumping 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Impact With Underwater Hazards 12. . . . . . . . . . . . . . . . . . . . . .
Selecting Accessories For Your Outboard 14. . . . . . . . . . . . . . .
Safe Boating Suggestions 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recording Serial Number 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Component Identification 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Propeller Selection 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transporting
Trailering Boat/Outboard 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel & Oil
Gasoline Recommendations 21. . . . . . . . . . . . . . . . . . . . . . . . . . .
Oil Recommendation 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filling Fuel Tank 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filling Remote Oil Tank 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filling Engine Mounted Oil Reservoir Tank 24. . . . . . . . . . . . . . .

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oa TABLE OF CONTENTS
Features & Controls
Remote Control Features 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Warning Horn System 26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Trim And Tilt 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Trim Operation 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tilting Operation 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Manual Tilting 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operation
Engine Break-in 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pre-Starting Check List 39. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating In Freezing Temperatures 40. . . . . . . . . . . . . . . . . . . .
Operating In Salt Water Or Polluted Water 40. . . . . . . . . . . . . . .
Operating At High Elevations 40. . . . . . . . . . . . . . . . . . . . . . . . . .
Setting Trim Angle While Running Engine at Idle Speed 41. . .
Operating in Shallow Water 41. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Starting The Engine 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gear Shifting 44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stopping The Engine 44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Emergency Starting 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance
Outboard Care 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Submerged Outboard 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selecting Replacement Parts For Your Outboard 47. . . . . . . . .
EPA Emissions Regulations 47. . . . . . . . . . . . . . . . . . . . . . . . . . .
Inspection And Maintenance Schedule 48. . . . . . . . . . . . . . . . . .
Flushing the Cooling System 50. . . . . . . . . . . . . . . . . . . . . . . . . .
Top Cowl Removal and Installation 52. . . . . . . . . . . . . . . . . . . . .
Flywheel Cover Removal and Installation 53. . . . . . . . . . . . . . . .
Fuel System 53. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(continued on next page)

3
oa TABLE OF CONTENTS
Maintenance(con’t.)
Steering Link Rod Fasteners 55. . . . . . . . . . . . . . . . . . . . . . . . . .
Fuse Replacement 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Corrosion Control Anodes 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Propeller Replacement 57. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Spark Plug Inspection 59. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Battery Inspection 59. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alternator Drive Belt Tension Adjustment 60. . . . . . . . . . . . . . . .
Lubrication Points 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking Power Trim Fluid 63. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gear Case Lubricant 65. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage
Storage Preparation 67. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting
Troubleshooting 70. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine Wiring Diagram
Engine Wiring Diagram 74. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MaintenanceLog
Maintenance Log 76. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The description and specifications contained herein were in effect
at the time this manual was approved for printing. Mercury Racing,
whose policy is one of continued improvement, reserves the right to
discontinue models at any time, to change specifications, designs,
methods, or procedures without notice and without incurring obliga-
tion.
Mercury Marine, Fond du Lac, Wisconsin U.S.A. Litho in U.S.A.
1999, Mercury Marine
The following are registered trademarks of Brunswick Corporation:
AutoBlend, Force, Jet-Prop, Mariner, Merc, Mercathode, MerCruis-
er, Mercury, Mercury Marine, Mercury Racing, Quicksilver, Ride-
Guide and Thruster

4
ob GENERAL INFORMATION
oba1
Boater’s Responsibilities
The boat driver is responsible for correct and safe operation of the
boat and safety of its occupants and general public. It is strongly rec-
ommended that each operator (driver) read and understand this en-
tire manual before operating the outboard.
Be sure at least one additional person on board is instructed in the
basics of starting and operating the outboard and boat handling in
case the driver is unable to operate the boat.
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Before Operating Your Outboard
Read this manual carefully. Safety and operating information that is
practiced along with using good common sense can help prevent
personal injury and product damage. If you have any questions,
contact your dealer.
This manual as well as safety labels posted on the outboard use
safety alerts to draw your attention to special safety instructions that
must be followed.
WARNING
WARNING – Hazards or unsafe practices which COULD result
in severe personal injury or death.
CAUTION
CAUTION – Hazards or unsafe practices which could result in
minor injury or product or property damage.

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ob GENERAL INFORMATION
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12
U.S. COAST GUARD CAPACITY
MAXIMUM HORSEPOWER XXX
MAXIMUM PERSON
CAPACITY (POUNDS) XXX
MAXIMUM WEIGHT
CAPACITY XXX
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Boat Horsepower Capacity
1Do 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.
WARNING
Overpowering a Boat Can Cause:
•Serious injury, death, or boat damage.
•Loss of Boat Control.
•Flotation Characteristics of Boat to be Altered from Placing
Too Much Weight on Transom.
•Boat to Break Apart, Particularly Around the Transom
Area.
obd2
High-Speed And High-Performance Boat
Operation
2If you are not familiar with high-performance boat operation we
recommend that you first request an orientation/demonstration
ride with your dealer or an operator experienced with your boat/
outboard combination. Refer to the “Guide to Hi-Performance
Boat Operation” booklet (Part Number 90-849250) included in
your literature packet.

6
ob GENERAL INFORMATION
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Lanyard Stop Switch
WARNING
Should the operator fall out of the boat, the possibility of seri-
ous injury or death from being run over by the boat can be
greatly reduced by stopping the engine immediately. Always
properly connect both ends of the stop switch lanyard – to the
stop switch and the operator.
1. 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. A lanyard stop switch can be installed as
an accessory – generally on the dashboard or side adjacent to
the operator’s position.
2. While activation of the lanyard stop switch will stop the engine
immediately, a boat will continue to coast for some distance de-
pending 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.

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ob GENERAL INFORMATION
Lanyard Stop Switch (Continued)
WARNING
Avoid serious injury or death from deceleration forces result-
ing from in accidental stop switch activation. The boat opera-
tor should never leave the operator’s station without first dis-
connecting the stop switch lanyard cord from themself.
Accidental or unintended activation of the Lanyard Stop Switch dur-
ing normal operation is a possibility and could cause any, or all, of
the following potentially hazardous situations:
1. 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 gear case or propeller.
2. Loss of power and directional control in heavy seas, strong cur-
rent or high winds.
3. Loss of control when docking.

8
ob GENERAL INFORMATION
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Protecting People In The Water
WHILE YOU ARE CRUISING
It is very difficult for a person in the water to take quick action to avoid
a boat heading in their direction even at slow speed.
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 (even coasting) even with the outboard
in neutral position, there is sufficient force by the water to rotate the
propeller. This neutral propeller rotation can cause serious injury.
WHILE BOAT IS STATIONARY
Shift outboard into neutral and shut off the engine before allowing
people to swim or be in the water near your boat.
WARNING
Stop your engine immediately whenever anyone in the water
is near your boat. Serious injury to the person in the water is
likely if contacted by a rotating propeller, a moving boat, a
moving gear case, or any solid device rigidly attached to a
moving boat or gear case.

9
GENERAL INFORMATION
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Courtesy of ABYC
1
a
Carbon Monoxide Risk
WARNING
Avoid the combination of a running engine and poor ventila-
tion. Prolonged exposure to carbon monoxide in sufficient
concentration can lead to unconsciousness, brain damage,
or death.
Carbon monoxide is a deadly gas that is odorless, colorless and
tasteless and is present in the exhaust fumes of all internal combus-
tion engines.
Early symptoms of carbon monoxide poisoning which should not be
confused with seasickness or intoxication, include headache, dizzi-
ness, drowsiness, and nausea.
SUFFICIENT FRESH AIR FLOW
1Example of desired air flow through the boat;
a. Ventilate passenger area, open side curtains, or forward
hatches to remove carbon monoxide fumes.

10
ob GENERAL INFORMATION
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Courtesy of ABYC
3
ba
2
ab
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Carbon Monoxide Risk (Continued)
INSUFFICIENT FRESH AIR FLOW
Under certain conditions, 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 rare, on a very calm day, swimmers and passengers in an
open stationary boat with a running engine, or near a running engine
may be exposed to a hazardous level of carbon monoxide.
Insufficient Air Flow Could Occur If:
2While boat is stationary:
a. Boat moored in a confined space with the engine running.
b. Boat is moored close to another boat with its engine running.
3While boat is moving:
a. Running the boat with the trim angle of the bow too high.
b. Running the boat with no forward hatches open (station
wagon effect).

11
ob GENERAL INFORMATION
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Wave And Wake Jumping
Operating recreational boats over waves and wakes is a natural part
of boating, However, when this activity is done with speed to force
the boat hull partially or completely out of the water, certain hazards
arise, particularly when the boat re-enters the water.
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 violently
veer in a new direction. Such a sharp change in direction or turn can
cause occupants to be thrown out of their seats or out of the boat.
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 pene-
trate under the water surface and “submarine” for an instant. This
will bring the boat nearly to a stop in an instant and can send the oc-
cupants flying forward. The boat may also steer sharply to one side.
WARNING
Avoid serious injury or death from being thrown within or out
of a boat when it lands after jumping a wave or wake. Avoid
wave or wake jumping whenever possible. Instruct all occu-
pants that if a wake or wave jump occurs, get low and hang
on to any boat hand hold.

12
ob GENERAL INFORMATION
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Impact With Underwater Hazards
Reduce speed and proceed with caution whenever you’re driving a
boat in shallow water areas or in areas where the waters are sus-
pected of having underwater obstacles that could be struck by the
outboard or the boat bottom. The most important thing you can
do to help reduce injury or impact damage from striking a float-
ing or underwater object is control the boat speed. Under these
conditions, boat speed should be kept to a minimum planing
speed (15 to 25 MPH).
WARNING
To avoid serious injury or death from all or part of an outboard
coming into the boat after striking a floating or underwater ob-
stacle maintain a top speed no greater than minimum planing
speed.
Striking a floating or underwater object could result in an infinite
number of situations. Some of these situations could result in the fol-
lowing:
•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. Such a sharp
change in direction or turn can cause occupants to be thrown out
of their seats or out of the boat.
•A rapid reduction in speed. This will cause occupants to be
thrown forward, even out of the boat.
•Impact damage to the outboard and/or boat.
(continued on next page)

13
GENERAL INFORMATION
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Impact With Underwater Hazards (Continued)
Keep in mind, one of the most important things you can do to help
reduce injury or impact damage in these situations is control the
boat speed. Boat speed should be kept to a minimum planing speed
when driving in waters known to have underwater obstacles.
After striking a submerged object, stop the engine as soon as pos-
sible and inspect the outboard for any broken or loose parts. If dam-
age is present or suspected, the outboard should be taken to an au-
thorized dealer for a thorough inspection and necessary repair.
The boat should also be checked for any hull fractures, transom
fractures, water leaks.
Operating a damaged outboard could cause additional damage to
other parts of the outboard, or could affect control of the boat. If con-
tinued running is necessary, do so at greatly reduced speeds.
WARNING
Avoid serious injury or death from from loss of boat control.
Continued boating with major impact damage can result in
sudden outboard component failure with or without subse-
quent impacts, Have the outboard thoroughly inspected and
any necessary repairs made.

14
GENERAL INFORMATION
obj1
Selecting Accessories For Your Outboard
Genuine Mercury Marine Accessories have been specifically de-
signed and tested for your outboard.
Mercury Marine accessories are available from Mercury Marine
dealers.
Some accessories not manufactured or sold by Mercury Marine are
not designed to be safely used with your outboard or outboard oper-
ating system. Acquire and read the installation, operation, and
maintenance manuals for all your selected accessories.
WARNING
Check with your dealer before installing accessories. Misuse
of acceptable accessories or the use of unacceptable acces-
sories can result in serious injury, death, or product failure.
Safe Boating Suggestions
In order to safely enjoy the waterways, familiarize yourself with local
and other governmental boating regulations and restrictions, and
consider the following suggestions.
Use Life Jackets. Have an approved life jacket of suitable size for
each person aboard and have it readily accessible (it is the law).
However we strongly recommend that everyone aboard wear their
life jacket.
Do not overload your boat. Most boats are rated and certified for
maximum load (weight) capacities (refer to your boat capacity
plate). If in doubt, contact your dealer or the boats manufacturer.
Perform safety checks and required maintenance. Follow a reg-
ular schedule and ensure that all repairs are properly made.
Know and obey all nautical rules and laws of the waterways.
Boat operators should complete a boating safety course. Courses
are offered in the U.S.A. by (1) The U.S. Coast Guard Auxiliary, (2)
The Power Squadron, (3) The Red Cross and (4) your state boating
law enforcement agency. Inquiries may be made to the Boating Hot-
line, 1-800-368-5647 or the Boat U.S. Foundation information num-
ber 1-800-336-BOAT. (continued on next page)

15
GENERAL INFORMATION
Safe Boating Suggestions (Continued)
Make sure everyone in the boat is properly seated. Don’t allow
anyone to sit or ride on any part of the boat that was not intended
for such use. This includes backs of seats, gunwales, transom, bow,
decks, raised fishing seats, any rotating fishing seat; 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.
Never be under the influence of alcohol or drugs while boating
(it is the law). They impair your judgment and greatly reduce your
ability to react quickly.
Prepare other boat operators. Instruct at least one person on
board in the basics of starting and operating the outboard and boat
handling in case the driver becomes disabled or falls overboard.
Passenger boarding. Stop the engine whenever passengers are
boarding, unloading or are near the back (stern) of the boat. Just
shifting the outboard into neutral is not sufficient.
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 operators view when operating the
boat above idle speed.
Never drive your boat directly behind a water skier in case the
skier falls. As an example, your boat traveling at 25 miles per hour
(40 km/hr) in 5 seconds will overtake a fallen skier who was 200 feet
(61m) in front of you.
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 val-
ue exceeds $500.00 or 4. there is complete loss of the boat. Seek
further assistance from local law enforcement.
(continued on next page)

16
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Recording Serial Number
19XX
XX
OGXXXXXX
XXXX
b
c
d
e
a
Record the following numbers from your engine as shown for future
reference.
a-Serial Number
b-Model Year
c-Model Designation
d-Year Manufactured
e-Certified Europe Insignia

17
ob GENERAL INFORMATION
Specifications
Models 300 - Pro Max 3.0L
Propshaft Horsepower 300
Propshaft Kilowatts 224
ECU Box Rev Limit 6200
Idle RPM (In or Out of Gear) 650 RPM
Weight 465 lbs.
(211 kg)
Piston Displacement 185 cu. in. (3044cc)
Bore 3.626 in. (92.1mm)
Stroke 3.00 in (76.2 mm)
Recommended Spark Plug Champion QL77CC (.035” Gap)
Firing Order 1-2-3-4-5-6
Idle Speed Pickup Timing Non Adjustable
Fuel Pressure 38-40 psi. (262-276 kPa)
Min. Water Pres.
@ 7500 -5500 RPM 12 psi. Minimum
Fleetmaster
Gear Ratio Torquemaster
Sportmaster
1.75:1
1.75:1
1.62:1 or 1.75:1
Recommended Gasoline Refer to Fuel Section
Recommended Oil Refer to Fuel Section
Recommended Gear Case
Oil Mercury Precision Hi-Performance Gear Lube (92-802854A1)
Gear Case Lubricant Cap. 27 fl. oz. (798 ml)
Battery Rating Minimum reserve capacity rating
of 100 minutes and CCA of 350
Charging System Output 60 amps Max. (847Watts)

18
GENERAL INFORMATION
Component Identification
1
3
4
5
6
7
8
10
11
12
13
14
15
8
8
14
9
2
1. Top Cowl
2. Cowl Latch (Front)
3. Cowl Latch (Rear)
4. Water Pump Indicator Hose
(Tell-Tail)
5. Bottom Cowl
6. Drive Shaft Housing
7. Anti-Ventilation Plate
8. Corrosion Anode(s)
9. Cowl Mount Trim Switch
10. Wiring Harness, Fuel line and
Control Cables (Install thru bot-
tom cowl)
11. Transom Brackets
12. Trim Adjustment Bolt
13. Gear Case
14. Cooling Water Intake Holes
15. Skeg