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Mercury 30 / 40 FourStroke (3 cylinder, carbureted, 1999 on, serial 0G760300 and above) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 30 / 40 FourStroke (3 cylinder, carbureted, 1999 on, serial 0G760300 and above) (30 to 40 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 30 and 40 FourStroke, starting model year 1999, starting serial 0G760300; 30/40 MH, 30/40 ELPT and 40 ELPT Bigfoot. 3 cylinder, over head camshaft, 747 cc (45.6 cu in), carbureted. Two gear cases: 3-1/4 in (83 mm) 2.00:1 and 4-1/4 in (108 mm) Bigfoot 2.31:1. Later 40 carbureted (serial 1C018826 and above) and 30/40 EFI (1C453840 and above) engines have their own sheets.

Quick answers

How much oil does a Mercury 30 / 40 FourStroke take?
Either 3 US quarts or 3 liters (3.0 L, 3 US qt). it does not give separate with-filter and without-filter amounts.
What engine oil does a Mercury 30 / 40 FourStroke use?
4-Stroke Outboard Oil, SAE 10W-30 for all temperatures; SAE 25W-40 may be used above 40 °F (4 °C). If not available, a premium 4-stroke engine oil meeting API SH, SG, SF, CF-4, CE, CD or CDII.
What gear oil does a Mercury 30 / 40 FourStroke use, and how much?
Premium Blend Gear Lube. Quantity: Standard 2.00:1 gear case: 440 ml (14.9 US fl oz). Bigfoot 2.31:1 gear case: 710 ml (24 US fl oz).
What spark plug does a Mercury 30 / 40 FourStroke use?
NGK DPR6EA-9, qty 3. Use resistive spark plugs only. Gap: 0.035 in (0.9 mm).
How often should a Mercury 30 / 40 FourStroke be serviced?
The factory schedule lists: Every 100 hours of use or once yearly, whichever occurs first; Every 300 hours of use or three years, whichever occurs first. 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 30 / 40 FourStroke?
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 30 / 40 FourStroke?
900 ± 25 rpm out of gear; 800 ± 25 rpm in forward gear. WOT range 5500 to 6000 rpm.
What is the propeller nut torque on a Mercury 30 / 40 FourStroke?
55 lb-ft (75 Nm), both gear cases; bend the retainer tabs against the nut.

Maintenance specs

Engine oil4-Stroke Outboard Oil, SAE 10W-30 for all temperatures; SAE 25W-40 may be used above 40 °F (4 °C). If not available, a premium 4-stroke engine oil meeting API SH, SG, SF, CF-4, CE, CD or CDII
Engine oil quantityEither 3 US quarts or 3 liters (3.0 L, 3 US qt). it does not give separate with-filter and without-filter amounts
Oil filterp/n 35-822626A2; or screw on until the gasket contacts the base, then 3/4 to 1 turn. Oil filter wrench 91-802653Q1
Engine oil drain plug17.5 lb-ft (23.5 Nm); lubricate the seal on the drain plug with oil
Gear lubePremium Blend Gear Lube
Gear lube quantityStandard 2.00:1 gear case: 440 ml (14.9 US fl oz). Bigfoot 2.31:1 gear case: 710 ml (24 US fl oz)
Gear lube plugsStandard gear case: 1 vent screw and 1 fill/drain screw, each with a sealing washer, 60 lb-in (7 Nm). Bigfoot gear case: 3 screws (front vent, rear vent, fill/drain), each with a sealing washer, 60 lb-in (7 Nm). Replace sealing washers if damaged
Gear case leak test pressure10 to 12 psi (69 to 83 kPa) for 5 minutes
Spark plugNGK DPR6EA-9, qty 3. Use resistive spark plugs only
Spark plug gap0.035 in (0.9 mm)
Spark plug torque150 lb-in (17 Nm); or finger tight then 1/4 turn, or 12.5 lb-ft (17 Nm)
Idle speed900 ± 25 rpm out of gear; 800 ± 25 rpm in forward gear. WOT range 5500 to 6000 rpm
ThermostatOpens at 136 to 143 °F (58 to 62 °C); full open 158 °F (70 °C); valve lift minimum 0.12 in (3 mm)
AnodesAnode screws (M6 x 25) 60 lb-in (7 Nm); Bigfoot gear housing anode screw (M6 x 40) 60 lb-in (7 Nm). Trim tab screw: standard 23 lb-ft (31.5 Nm), Bigfoot 22 lb-ft (30 Nm). Engine block anode covers 70 lb-in (8 Nm), on manual start serial 0T426439 and below and electric start serial 0T427437 and below (three anodes in the block, behind the ignition coils)
Propeller nut55 lb-ft (75 Nm), both gear cases; bend the retainer tabs against the nut
Power trim fluidPower Trim & Steering Fluid, or automotive ATF if not available. Tilt full up on the tilt support lock; level even with the bottom of the fill hole
Valve clearance, coldIntake 0.15 to 0.25 mm (0.006 to 0.010 in); exhaust 0.25 to 0.35 mm (0.010 to 0.014 in)

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 of use or once yearly, whichever occurs first

    Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets

    Check: spark plugs, fuel filter, thermostat, anodes

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

    Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, fuel filter, thermostat, anodes

  3. Every 300 hours of use or three years, whichever occurs first

    Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, fuel filter, 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 30/40 FourStroke service manual, 90-857046R1. 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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