Mercury 6 / 8 / 9.9 EFI FourStroke service guide

Quick answers

How much oil does a Mercury 6 / 8 / 9.9 EFI FourStroke take?

About 800 ml (27 fl oz). No oil filter.

What engine oil does a Mercury 6 / 8 / 9.9 EFI FourStroke use?

10W-30 all temperatures; 25W-40 above 4 °C (40 °F).

What gear oil does a Mercury 6 / 8 / 9.9 EFI FourStroke use, and how much?

Premium Gear Lubricant or GL5 SAE 80-90; Premium or High-Performance. Quantity: Standard (2.08:1) about 320 ml (10.8 fl oz); Command Thrust (2.42:1) about 370 ml (12.5 fl oz).

What spark plug does a Mercury 6 / 8 / 9.9 EFI FourStroke use?

NGK DCPR6E.

How often should a Mercury 6 / 8 / 9.9 EFI FourStroke be serviced?

The factory schedule lists: 100 hours or before storage; 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 6 / 8 / 9.9 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 propeller nut torque on a Mercury 6 / 8 / 9.9 EFI FourStroke?

11.5 N·m (102 lb·in), then a cotter pin.

Maintenance specs

Engine oil	10W-30 all temperatures; 25W-40 above 4 °C (40 °F)
Engine oil quantity	About 800 ml (27 fl oz). No oil filter
Oil drain plug bolt	24 N·m (17.7 lb·ft)
Gear lubricant	Premium Gear Lubricant or GL5 SAE 80-90; Premium or High-Performance
Gearcase capacity	Standard (2.08:1) about 320 ml (10.8 fl oz); Command Thrust (2.42:1) about 370 ml (12.5 fl oz)
Gearcase plugs	6.8 N·m (60 lb·in) in the parts tables; vent screw 6.7 N·m (60 lb·in) in the fill procedure
Spark plug	NGK DCPR6E
Spark plug torque	27 N·m (20 lb·ft), or finger tight then 1/4 turn
Thermostat	Starts to open 60 ± 1.5 °C (140 °F); fully open 75 ± 1.5 °C (167 °F); lift 3 mm (0.12 in)
Water pressure	Idle 50 kPa (7.2 psi); WOT 95 kPa (13.7 psi)
Anode / trim tab screw	5.6 N·m (50 lb·in); engine anode cover screws 6 N·m (53 lb·in)
Propeller nut	11.5 N·m (102 lb·in), then a cotter pin
Power tilt fluid	Power Trim and Steering Fluid or ATF Dexron III
Valve clearance, cold	IN 0.13 to 0.17 mm (0.005 to 0.007 in); EX 0.18 to 0.22 mm (0.007 to 0.009 in); locknut 7 N·m (62 lb·in)
Timing belt	Inspect 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. 100 hours or before storage

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

   Check: thermostat, anodes

3. 3 years or 300 hours

   Replace: engine oil, 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 6/8/9.9hp EFI FourStroke service manual, 90-8M0239276. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.