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Mercury 4 / 5 / 6 FourStroke service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 4 / 5 / 6 FourStroke (4 to 6 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 4, 5 and 6 hp FourStroke, 1 cylinder, carbureted, serial 0R411838 and above.

Quick answers

How much oil does a Mercury 4 / 5 / 6 FourStroke take?
About 450 ml (15 fl oz). No oil filter.
What engine oil does a Mercury 4 / 5 / 6 FourStroke use?
SAE 10W-30 all temperatures; 25W-40 above 4 °C (40 °F).
What gear oil does a Mercury 4 / 5 / 6 FourStroke use, and how much?
Premium or High Performance Gear Lubricant (fill procedure names Premium). Quantity: About 195 ml. Fill until it comes out the vent.
What spark plug does a Mercury 4 / 5 / 6 FourStroke use?
Two plugs listed: NGK DCPR6E and NGK DPR6E. Use the one on the emission decal. Gap: 0.9 mm (0.035 in).
How often should a Mercury 4 / 5 / 6 FourStroke be serviced?
The factory schedule lists: Every 100 hours or once a year. 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 4 / 5 / 6 FourStroke?
The factory schedule says to replace it at 100 hours, and we follow that. In any case we never let it go longer than a year in Hawaiʻi's salt water.
What is the idle speed of a Mercury 4 / 5 / 6 FourStroke?
Neutral 1,250 to 1,350, forward 1,050 to 1,150 r/min; carburetor tables 1,300 ± 50 / 1,100 ± 50.
What is the propeller nut torque on a Mercury 4 / 5 / 6 FourStroke?
17 N·m (150 lb·in) with a cotter pin.

Maintenance specs

Engine oilSAE 10W-30 all temperatures; 25W-40 above 4 °C (40 °F)
Engine oil quantityAbout 450 ml (15 fl oz). No oil filter
Gear lubricantPremium or High Performance Gear Lubricant (fill procedure names Premium)
Gearcase capacityAbout 195 ml. Fill until it comes out the vent
Spark plugTwo plugs listed: NGK DCPR6E and NGK DPR6E. Use the one on the emission decal
Spark plug gap0.9 mm (0.035 in)
Idle speedNeutral 1,250 to 1,350, forward 1,050 to 1,150 r/min; carburetor tables 1,300 ± 50 / 1,100 ± 50
ThermostatStarts to open 50 ± 1.5 °C (122 °F); fully open 63 ± 1.5 °C (145 °F); lift 3 mm (0.12 in)
Water pressure1300 r/min 16 to 25 kPa (2.3 to 3.6 psi); 5000 r/min 55 to 104 kPa (8 to 15 psi)
Anode bolt8 N·m (71 lb·in); replace at more than 50% gone
Propeller nut17 N·m (150 lb·in) with a cotter pin
Valve clearanceIN 0.06 to 0.14 mm (0.0024 to 0.0055 in); EX 0.11 to 0.19 mm (0.0043 to 0.0075 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 or once a year

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

    Check: fuel filter, anodes

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

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

    Check: fuel filter, anodes

Source: Mercury 4/5/6 FourStroke service manual, 90-879276001. 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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