1987 Mercury 115 HP Outboard Manual

The 1987 Mercury 115 HP Outboard is a powerful marine engine featuring a 115 horsepower V6 configuration, oil injection system, Thunderbolt CD ignition, power trim and tilt, through-hub exhaust, and standard 20-inch shaft length. This manual covers essential information for operation, maintenance, troubleshooting, and specifications of this reliable marine powerplant.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Operation 6. Maintenance Schedule 7. Fuel System 8. Electrical System 9. Cooling System 10. Propeller Information 11. Troubleshooting

Features at a Glance

Key components: V6 engine block, oil injection system, Thunderbolt CD ignition, power trim/tilt, through-hub exhaust, standard controls.

Feature	Description
Engine Type	V6 Outboard
Horsepower	115 HP at 5250 RPM
Displacement	172.4 cubic inches (2.8L)
Ignition System	Thunderbolt CD
Fuel System	Oil Injection with 3 carburetors
Gear Ratio	1.85:1
Shaft Length	20 inches standard
Weight	Approximately 315 lbs
Starting System	Electric with manual backup
Exhaust System	Through-hub design

Installation

Proper installation ensures optimal performance and safety.

Select appropriate transom: Ensure transom can support engine weight and horsepower.
Mount engine: Use correct mounting bolts and follow torque specifications.
Connect steering system: Install steering cable according to manufacturer instructions.
Connect control cables: Route and connect throttle/shift cables properly.
Connect electrical: Battery cables, ignition, and trim/tilt wiring.
Install propeller: Use correct propeller for intended use.

WARNING! Engine is heavy; use proper lifting equipment. Ensure all connections are secure before operation.

First-Time Setup

Initial setup procedures for new installation.

Fuel system: Fill oil injection tank with Mercury Premium Plus oil.
Fuel mixture: Use 87 octane gasoline with proper fuel/oil ratio.
Battery installation: Connect 12V marine battery with proper polarity.
Control box installation: Mount and connect Mercury control box.
Break-in procedure: Follow recommended break-in schedule for first 10 hours.

CAUTION! Always use marine-grade components. Follow all safety procedures during setup.

Specifications

Engine Type: V6 Outboard
Horsepower: 115 HP @ 5250 RPM
Displacement: 172.4 cu in (2.8L)
Bore x Stroke: 3.50" x 2.99"
Full Throttle Range: 5000-5500 RPM
Fuel System: Oil injection with 3 carburetors
Ignition: Thunderbolt CD
Gear Ratio: 1.85:1
Recommended Fuel: 87 octane gasoline
Weight: 315 lbs (20" shaft)

Controls and Operation

Standard Mercury control box operation and engine controls.

Control Box: Throttle/shift lever, ignition switch, choke, trim/tilt switches.

Starting Procedure: Turn key to ON position, advance throttle slightly, turn to START. Cold starts may require choke. Operation: Allow engine to warm up at idle. Monitor temperature and oil injection system. Shifting: Smooth transitions between forward, neutral, and reverse.

Maintenance Schedule

Regular maintenance ensures long engine life and reliable operation.

Every 100 hours: Change gear lube, inspect water pump
Every 200 hours: Replace spark plugs, fuel filter
Annual: Fog engine for storage, check battery
Every 2 years: Replace water pump impeller
As needed: Grease fittings, check propeller

Tip: Keep maintenance records for warranty and resale value.

Fuel System

Oil injection system with three carburetors for optimal fuel delivery.

Fuel Requirements: 87 octane gasoline with Mercury Premium Plus oil
Oil Injection: Automatic oil mixing; monitor oil level
Carburetors: Three 1.25" venturi carburetors
Fuel Pump: Diaphragm type with check valves
Fuel Filter: Replace annually or every 200 hours

WARNING! Never operate without proper oil mixture. Check oil injection system regularly.

Electrical System

Thunderbolt CD ignition and 12V electrical system.

Ignition: Thunderbolt CD system provides reliable spark. Charging System: 16 amp alternator for battery charging. Starting System: Electric starter with manual backup. Trim/Tilt: 12V electric motor with up/down controls.

Cooling System

Water-cooled system with thermostat and water pump.

Water Pump: Rubber impeller type, replace every 2 years. Thermostat: Maintains proper operating temperature. Tell-tale: Water stream indicates proper cooling operation.

CAUTION! Always check for water discharge before operating at high RPM.

Propeller Information

Proper propeller selection for optimal performance.

Standard Prop: 13.25" x 17" aluminum
Diameter Range: 13" - 14.5"
Pitch Range: 15" - 21"
Material: Aluminum standard, stainless steel optional

Select propeller based on boat type, load, and intended use to maintain 5250 RPM at wide open throttle.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, or compression	Check fuel supply, spark plugs, compression
Overheating	Water pump, thermostat	Replace water pump impeller, check thermostat
Poor performance	Fuel system, propeller	Clean carburetors, check propeller condition
No oil injection	Oil pump, lines	Check oil pump operation, inspect lines
Electrical issues	Battery, connections	Test battery, clean connections

Service: Contact authorized Mercury Marine dealer for major repairs.

Support: Mercury Marine Customer Service for technical assistance.