Mercury / Mariner 30 / 40 two-stroke, 2 cylinder (644 cc) service guide

Quick answers

What two-stroke oil does a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder use?

TC-W III 2-Cycle Outboard Oil.

What is the fuel to oil ratio for a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder?

Models without oil injection: 25:1 (4%) in the first tank of fuel, then 50:1 (2%). Models with oil injection: 50:1 (2%) in the first tank of fuel on top of the injected oil, then no oil in the gasoline.

What gear oil does a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder use, and how much?

Premium Gear Lubricant; do not use automotive grease. Quantity: 440.6 ml (14.9 fl oz), 2.00:1 gearcase; fill until excess lubricant flows from the vent hole.

What spark plug does a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder use?

NGK BPZ8H-N-10, 18 mm hex, qty 2. Gap: 1.0 mm (0.040 in).

How often should a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder 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 / Mariner 30 / 40 two-stroke, 2 cylinder?

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 / Mariner 30 / 40 two-stroke, 2 cylinder?

700 to 800 RPM in forward gear; idle mixture screw 1-1/2 ± 1/4 turns out.

What is the propeller nut torque on a Mercury / Mariner 30 / 40 two-stroke, 2 cylinder?

Minimum 75 N·m (55 lb ft), then bend the tab washer against the nut; re-tighten after first use.

Maintenance specs

Two-stroke engine oil	TC-W III 2-Cycle Outboard Oil
Fuel to oil ratio	Models without oil injection: 25:1 (4%) in the first tank of fuel, then 50:1 (2%). Models with oil injection: 50:1 (2%) in the first tank of fuel on top of the injected oil, then no oil in the gasoline
Gear oil	Premium Gear Lubricant; do not use automotive grease
Gear oil quantity	440.6 ml (14.9 fl oz), 2.00:1 gearcase; fill until excess lubricant flows from the vent hole
Gear oil fill and vent plugs	Fill plug (magnetic if equipped) and vent plug: 6.2 N·m (55 lb in), new gaskets on both. Install the vent plug first, then the fill plug
Lower unit holding pressure	68.9 to 103.4 kPa (10 to 15 psi) at the vent hole, must hold 5 minutes; turn the drive shaft and prop shaft and move the shift rod while pressurized
Spark plug	NGK BPZ8H-N-10, 18 mm hex, qty 2
Spark plug gap	1.0 mm (0.040 in)
Spark plug torque	27 N·m (20 lb ft)
Idle speed	700 to 800 RPM in forward gear; idle mixture screw 1-1/2 ± 1/4 turns out
Thermostat	130 degree thermostat (parts list); must begin to open 3 °C (5 °F) above the figure stamped on its bottom. A poppet valve also opens at 900 to 1000 RPM or 3000 to 3500 RPM (1998 and newer)
Anodes	The trim tab is the anode; models with the longer transom brackets have a second anode. Replace the trim tab if 50% or more is consumed, never paint it. Trim tab bolt 31.6 N·m (23.3 lb ft)
Propeller nut	Minimum 75 N·m (55 lb ft), then bend the tab washer against the nut; re-tighten after first use
Power trim fluid	Power Trim and Steering Fluid, or ATF Type F, FA or Dexron III; level even with the bottom of the fill hole with the outboard tilted full up

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

   Check: spark plugs, fuel filter, anodes

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

   Replace: gear case oil, gear case plug gaskets, water pump impeller

   Check: spark plugs, fuel filter, anodes

3. Every 300 hours or 3 years

   Replace: gear case oil, gear case plug gaskets, water pump impeller

   Check: spark plugs, fuel filter, 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/Mariner 30/40 2-Cylinder service manual, 90-826148R03, August 2003. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.