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Mercury 15 / 20 EFI FourStroke service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 15 / 20 EFI FourStroke (15 to 20 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 15 and 20 EFI FourStroke, 2 cylinder, serial 0R833820 and above.

Quick answers

How much oil does a Mercury 15 / 20 EFI FourStroke take?
1.0 L (1.1 US qt).
What engine oil does a Mercury 15 / 20 EFI FourStroke use?
FC-W 10W-30 all temperatures; FC-W 25W-40 above 4 °C (40 °F).
What gear oil does a Mercury 15 / 20 EFI FourStroke use, and how much?
Premium Gear Lubricant or GL5 SAE 80W-90; Premium or High Performance. Quantity: About 460 ml (15.6 fl oz).
What spark plug does a Mercury 15 / 20 EFI FourStroke use?
NGK DCPR6E. Gap: 0.9 mm (0.035 in).
How often should a Mercury 15 / 20 EFI FourStroke 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 15 / 20 EFI 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 15 / 20 EFI FourStroke?
900 to 1,000 r/min.
What is the propeller nut torque on a Mercury 15 / 20 EFI FourStroke?
12 N·m (106 lb·in); tighten further to line up the cotter pin hole.

Maintenance specs

Engine oilFC-W 10W-30 all temperatures; FC-W 25W-40 above 4 °C (40 °F)
Engine oil quantity1.0 L (1.1 US qt)
Oil filter3/4 to 1 turn after the gasket touches; torque tables list 18.0 N·m (159.3 lb·in)
Oil drain plug24.0 N·m (17.7 lb·ft)
Gear lubricantPremium Gear Lubricant or GL5 SAE 80W-90; Premium or High Performance
Gearcase capacityAbout 460 ml (15.6 fl oz)
Gearcase plugs (2)13.0 N·m (115 lb·in)
Spark plugNGK DCPR6E
Spark plug gap0.9 mm (0.035 in)
Spark plug torque18.0 N·m (159.3 lb·in)
Idle speed900 to 1,000 r/min
ThermostatStarts to open 50 to 54 °C (122 to 129 °F); fully open 60 to 64 °C (140 to 147 °F); lift 4.0 mm (0.157 in)
Water pressureIdle 9 to 18 kPa (1.3 to 2.6 psi); WOT 59 to 118 kPa (8.6 to 17.2 psi)
Anode fastenersMidsection, lower mount and transom bracket anodes 6.0 N·m (53.1 lb·in); powerhead anode screw 2.0 N·m (17.7 lb·in), anode plug 18.0 N·m (159.3 lb·in)
Propeller nut12 N·m (106 lb·in); tighten further to line up the cotter pin hole
Valve clearanceIN 0.13 to 0.17 mm (0.005 to 0.007 in); EX 0.18 to 0.22 mm (0.007 to 0.008 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 filter, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin

    Check: 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, propeller cotter pin, water pump impeller

    Check: fuel filter, thermostat, anodes

  3. Every 300 hours or 3 years

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

    Check: 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 15/20 EFI FourStroke service manual, 90-8M0125265. 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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