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Mercury 25 / 30 EFI FourStroke (3 cylinder, 500 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury 25 / 30 EFI FourStroke (3 cylinder, 500 cc) (25 to 30 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury 25 and 30 HP EFI FourStroke, including SeaPro and 25 Jet, starting serial 1R154758; 3 cylinder, 500 cc.

Quick answers

How much oil does a Mercury 25 / 30 EFI FourStroke take?
1.4 L (1.5 US qt). Older 8M0105568: 1.8 L (1.9 US qt).
What engine oil does a Mercury 25 / 30 EFI FourStroke use?
FC-W 10W-30 all temperatures; FC-W 25W-40 above 4 °C (40 °F). Older: same.
What gear oil does a Mercury 25 / 30 EFI FourStroke use, and how much?
Premium Gear Lubricant or SAE 80W90 API GL4; Premium or High-Performance. Older: Premium or GL5 SAE 80-90. Quantity: About 460 ml (15.6 fl oz), ratio 2.17:1. Older 8M0105568: 350 ml (11.8 fl oz), ratio 1.92:1.
What spark plug does a Mercury 25 / 30 EFI FourStroke use?
NGK DCPR6E, qty 3. Gap: 0.9 mm (0.035 in). Older: 0.8 to 0.9 mm (0.031 to 0.035 in).
How often should a Mercury 25 / 30 EFI FourStroke be serviced?
The factory schedule lists: Every 100 hours or before storage; Every 3 years or 300 hours. 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 25 / 30 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 25 / 30 EFI FourStroke?
875 ± 25 r/min in gear. Older: 850 ± 25 r/min.
What is the propeller nut torque on a Mercury 25 / 30 EFI FourStroke?
25 N·m (18.4 lb·ft) plus cotter pin; tighten further to line up the hole.

Maintenance specs

Engine oilFC-W 10W-30 all temperatures; FC-W 25W-40 above 4 °C (40 °F). Older: same
Engine oil quantity1.4 L (1.5 US qt). Older 8M0105568: 1.8 L (1.9 US qt)
Oil filterOil the gasket, then 3/4 to 1 turn after it touches the base. Older: same
Oil drain plug24.0 N·m (17.7 lb·ft); oil the seal. Older: 23.7 N·m (17.5 lb·ft)
Gear lubricantPremium Gear Lubricant or SAE 80W90 API GL4; Premium or High-Performance. Older: Premium or GL5 SAE 80-90
Gearcase capacityAbout 460 ml (15.6 fl oz), ratio 2.17:1. Older 8M0105568: 350 ml (11.8 fl oz), ratio 1.92:1
Gearcase plugsPlug 4 N·m (35.4 lb·in) from the exploded view.
Spark plugNGK DCPR6E, qty 3
Spark plug gap0.9 mm (0.035 in). Older: 0.8 to 0.9 mm (0.031 to 0.035 in)
Spark plug torque18 N·m (159.3 lb·in); anti-seize on the threads at 100 h. Older 8M0105568: 20 N·m (14 lb·ft)
Idle speed875 ± 25 r/min in gear. Older: 850 ± 25 r/min
ThermostatStarts to open 60 ± 2.0 °C (140 °F); fully open 75 ± 2.0 °C (167 °F); lift 3 mm (0.12 in). Older: 60 ± 1.5 °C / 75 ± 1.5 °C, lift 3 mm
Water pressure (at the gearcase pump)Idle 12.9 kPa (1.9 psi); WOT 44.8 kPa (6.5 psi). Older: idle 50 kPa (7.2 psi), WOT 95 kPa (13.7 psi)
AnodesTrim tab is an anode: screw 6 N·m (53.1 lb·in). More anodes on the transom bracket, lower mount and swivel bracket, each with a 6 N·m (53.1 lb·in) screw. Older: block anode and trim tab, 6 N·m
Propeller nut25 N·m (18.4 lb·ft) plus cotter pin; tighten further to line up the hole
Power trim fluidPower Trim and Steering Fluid or ATF Dexron III; system 263 ml (8.9 fl oz)
Valve clearance, coldIN 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). Older: same
Timing beltInspect at 3 years / 300 h for cracks, worn cogs, oil swelling, worn edges.

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 before storage

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

    Check: 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, fuel filter, gear case oil, gear case plug gaskets, water pump impeller

    Check: thermostat, anodes

  3. Every 3 years or 300 hours

    Replace: engine oil, oil filter, oil drain plug gasket, spark plugs, fuel filter, gear case oil, gear case plug gaskets, 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 25/30 HP EFI FourStroke service manual, 90-8M0186413. 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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