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Mercury V6 / V8 FourStroke (CMS and AMS, 2018 on) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury V6 / V8 FourStroke (CMS and AMS, 2018 on) (175 to 300 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: V6 175/200/225 (3.4 L) and V8 200/225/250/300 (4.6 L) FourStroke with conventional midsection (CMS), and V8 250/300 with advanced midsection (AMS). Both manuals start at serial 2B529482 (covers).

Quick answers

How much oil does a Mercury V6 / V8 FourStroke take?
6.6 L (7.0 US qt) with filter.
What engine oil does a Mercury V6 / V8 FourStroke use?
NMMA FC-W SAE 10W-30. SeaPro: FC-W 25W-40 or 10W-30. 150R/200R racing: Mercury Racing 10W-30 MRX full synthetic.
What gear oil does a Mercury V6 / V8 FourStroke use, and how much?
High Performance Gear Lubricant (5.44 in.: SAE 90 API GL-4 High Performance). Sport Master: SAE 85W-90 Extreme Performance Gear Lube. Quantity: 4.8 in.: RH 710 mL (24.0 fl oz), LH 810 mL (27.4 fl oz). 5.44 in.: RH 720 mL (24.4 fl oz), LH 680 mL (23.0 fl oz). SeaPro 5.44 in.: 980 mL (33.1 fl oz). Torque Master: 520 mL (17.5 fl oz). Sport Master: 620 mL (20.9 fl oz).
What spark plug does a Mercury V6 / V8 FourStroke use?
NGK LKAR7C9, 14 mm hex. Gap: 0.9 mm (0.035 in.).
How often should a Mercury V6 / V8 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 V6 / V8 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 V6 / V8 FourStroke?
600 r/min in neutral, warm; idle charge up to 725 r/min; troll 550 to 1,000 r/min.
What is the propeller nut torque on a Mercury V6 / V8 FourStroke?
75 N·m (55.3 lb·ft); on Flo-Torq II and IV bend the tabs.

Maintenance specs

Engine oilNMMA FC-W SAE 10W-30. SeaPro: FC-W 25W-40 or 10W-30. 150R/200R racing: Mercury Racing 10W-30 MRX full synthetic
Engine oil quantity6.6 L (7.0 US qt) with filter
Oil drain valve15 N·m (132.7 lb·in). Open no more than 2-1/2 turns; use a 12 mm (7/16 in.) ID hose, or pump out through the dipstick tube
Gear lubricantHigh Performance Gear Lubricant (5.44 in.: SAE 90 API GL-4 High Performance). Sport Master: SAE 85W-90 Extreme Performance Gear Lube
Gearcase capacity (approximate)4.8 in.: RH 710 mL (24.0 fl oz), LH 810 mL (27.4 fl oz). 5.44 in.: RH 720 mL (24.4 fl oz), LH 680 mL (23.0 fl oz). SeaPro 5.44 in.: 980 mL (33.1 fl oz). Torque Master: 520 mL (17.5 fl oz). Sport Master: 620 mL (20.9 fl oz)
Gear fill/drain and level/vent plugs11.3 N·m (100 lb·in); replace damaged sealing washers
Gear housing pressure test (no lube)4.8 in. and Torque Master: 103.4 kPa (15 psi) for 15 minutes. 5.44 in.: 103.4 kPa (15 psi) for 5 minutes. Sport Master: 137.9 kPa (20 psi) for 5 minutes
Spark plugNGK LKAR7C9, 14 mm hex
Spark plug gap0.9 mm (0.035 in.)
Idle speed600 r/min in neutral, warm; idle charge up to 725 r/min; troll 550 to 1,000 r/min
ThermostatStarts to open 57 to 61 °C (134.6 to 141.8 °F); fully open 77 °C (170.6 °F); stroke at least 10.0 mm (0.39 in.)
Water pressure600 r/min 10 to 20 kPa (1.5 to 2.9 psi); 6000 r/min 60 to 260 kPa (8.7 to 37.7 psi)
Propeller nut75 N·m (55.3 lb·ft); on Flo-Torq II and IV bend the tabs
Power trim fluidPower Trim and Steering Fluid, or ATF Type F, FA, Dexron II or III. CMS: level with the bottom of the fill hole, tilted up. AMS: on the tilt support, about 25 mm (1 in.) below the top of the fill neck; cap 1/4 turn only
Valve lash clearanceIN 0.125 to 0.225 mm (0.005 to 0.009 in.); EX 0.300 to 0.400 mm (0.012 to 0.016 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

    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 or 3 years

    Replace: engine oil, oil filter, oil drain plug gasket, spark plugs, gear case oil, gear case plug gaskets, 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 V6 175/200/225 and V8 200/225/250/300 FourStroke CMS service manual, 90-8M0227198; Mercury V8 250/300 FourStroke AMS service manual, 90-8M0182077. 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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