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Mercury 2 / 2.5 / 3 / 3.3 two-stroke (74.6 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 2 / 2.5 / 3 / 3.3 two-stroke (74.6 cc) (2 to 3.3 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: The 2, 2.5 and 3 hp have no gear shift (360° turn) and the non-shift gear housing; the 3.3 hp has a neutral - forward shift and the shifting gear housing. Magneto (points) ignition or CDI ignition, each with its own section. one section is headed Driveshaft Housing 0T894577 and Above.

Quick answers

What two-stroke oil does a Mercury 2 / 2.5 / 3 / 3.3 two-stroke use?
Premium TC-W3 outboard oil.
What is the fuel to oil ratio for a Mercury 2 / 2.5 / 3 / 3.3 two-stroke?
50:1 (2%); 25:1 (4%) break-in, for the first tank of fuel. Automotive unleaded, minimum 87 octane, maximum 10% ethanol.
What gear oil does a Mercury 2 / 2.5 / 3 / 3.3 two-stroke use, and how much?
Premium or High-Performance Gear Lubricant. Quantity: Non-shift (2, 2.5, 3 hp): 90 mL (3 fl oz). Shifting (3.3 hp): 135 mL (4.5 fl oz). Approximate; fill at the fill/drain hole until it appears at the vent hole.
What spark plug does a Mercury 2 / 2.5 / 3 / 3.3 two-stroke use?
NGK BPR6HS-10 or Champion RL87YC, qty 1. Gap: 1.0 mm (0.040 in.).
How often should a Mercury 2 / 2.5 / 3 / 3.3 two-stroke be serviced?
The factory schedule lists: Every 100 hours or once a year; Every 300 hours or 3 years. In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
When should the water pump impeller be replaced on a Mercury 2 / 2.5 / 3 / 3.3 two-stroke?
The factory schedule says to replace it at 300 hours. In Hawaiʻi's warm salt water we replace it every 200 hours or 1 year, whichever comes first, because a worn impeller is the most common cause of overheating.
What is the idle speed of a Mercury 2 / 2.5 / 3 / 3.3 two-stroke?
1000 to 1100 RPM in gear.
What is the propeller nut torque on a Mercury 2 / 2.5 / 3 / 3.3 two-stroke?
No nut: the propeller is driven by a drive (shear) pin and held by a cotter pin. Grease the whole shaft with 2-4-C with PTFE; fit a new cotter pin.

Maintenance specs

Two-stroke engine oilPremium TC-W3 outboard oil
Fuel to oil ratio50:1 (2%); 25:1 (4%) break-in, for the first tank of fuel. Automotive unleaded, minimum 87 octane, maximum 10% ethanol
Gear oilPremium or High-Performance Gear Lubricant
Gear oil quantityNon-shift (2, 2.5, 3 hp): 90 mL (3 fl oz). Shifting (3.3 hp): 135 mL (4.5 fl oz). Approximate; fill at the fill/drain hole until it appears at the vent hole.
Gear oil fill/drain and vent plugsFill/drain plug and vent plug, each with a sealing washer (2 plugs, 2 gaskets). Shifting gear housing: 6.8 N·m (60 lb-in). Install the vent plug before taking the lubricant tube out, then the fill/drain plug
Lower unit holding pressureNon-shift gear housing: should hold 70 kPa (10 psi) of air.
Spark plugNGK BPR6HS-10 or Champion RL87YC, qty 1
Spark plug gap1.0 mm (0.040 in.)
Spark plug torque27 N·m (20 lb-ft), or finger tight and then 1/4 turn; hex 16 mm (5/8 in.)
Idle speed1000 to 1100 RPM in gear
AnodeOne on the gearcase, under the anti-ventilation plate on the shifting gear housing; replace when 50% or more consumed, never paint; anode bolt (M6 x 16) 5.6 N·m (50 lb-in)
PropellerNo nut: the propeller is driven by a drive (shear) pin and held by a cotter pin. Grease the whole shaft with 2-4-C with PTFE; fit a new cotter pin
Power trim and tiltNone: manual tilt, 4 tilt pin positions

Service schedule

The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.

  1. Every 100 hours or once a year

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin

    Check: thermostat, anodes

  2. Every 200 hours or 1 year (our Hawai‘i yearly service) Hawai‘i

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: thermostat, anodes

  3. Every 300 hours or 3 years

    Replace: spark plugs, gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: thermostat, anodes

We replace the water pump impeller at every service from 200 hours up, which can be sooner than the factory schedule, because of Hawaiʻi’s warm salt water.

Source: Mercury 2/2.5/3/3.3 HP 2-Stroke service manual, 90-8M0131799, July 2020. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

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