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Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke (209 and 262 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke (209 and 262 cc) (6 to 15 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: 6, 8, 8 Sailmate, 9.9, 9.9 Sailpower, XR10 / MAG10 / Viking 10, 10 Sea Pro / Marathon, 15 and 15 Sea Pro / Marathon two-stroke twins, cross flow, starting model year 1986: serial 0A197112 and above (USA), 09503295 and up (Belgium) (cover). 1995 and newer 9.9, 9.9 Sailpower, 10 and 15 are all 262 cc. Premixed fuel and oil.

Quick answers

What two-stroke oil does a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke use?
2 Cycle Outboard Oil.
What is the fuel to oil ratio for a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke?
Pre-mixed gasoline and oil: 25:1 during break-in, 50:1 after break-in.
What gear oil does a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke use, and how much?
Quicksilver Gear Lube Premium Blend (the fill procedure says Premium Gear Lubricant or High Performance Gear Lubricant; do not use automotive grease). Quantity: 200 ml (6.8 fl oz), 2.00:1 gearcase; fill through the fill hole until lubricant flows out of the vent hole with no air bubbles.
What spark plug does a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke use?
1994: 6/8/9.9 NGK BP8H-N-10, 10/15 NGK BP8HS-15. 1995 and newer: 6/8 NGK BP8H-N-10, 9.9/10/15 NGK BP8HS-15. NGK BPZ8H-N-10 where radio interference suppression is required. Qty 2. Gap: BP8H-N-10 engines (6/8, and 1994 9.9): 1.0 mm (0.040 in). BP8HS-15 engines (10/15, and 1995 and newer 9.9): 1.5 mm (0.060 in).
How often should a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke 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 / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke?
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 / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke?
6: 650 ± 75 RPM; 8: 725 ± 50; 9.9 / 9.9 Sailpower: 725 ± 50; 10 Sea Pro / Marathon: 850 ± 50; XR / MAG / Viking 10: 725 ± 50; 15: 725 ± 50. Fast idle 1500 to 2000 RPM.
What is the propeller nut torque on a Mercury / Mariner 6 / 8 / 9.9 / 10 / 15 two-stroke?
7.9 N·m (70 lb in) in the installation procedure.

Maintenance specs

Two-stroke engine oil2 Cycle Outboard Oil
Fuel to oil ratioPre-mixed gasoline and oil: 25:1 during break-in, 50:1 after break-in
Gear oilQuicksilver Gear Lube Premium Blend (the fill procedure says Premium Gear Lubricant or High Performance Gear Lubricant; do not use automotive grease)
Gear oil quantity200 ml (6.8 fl oz), 2.00:1 gearcase; fill through the fill hole until lubricant flows out of the vent hole with no air bubbles
Gear oil fill/drain and vent plugsNew gaskets on both; install the vent screw before removing the lubricant tube, then quickly install the fill screw
Spark plug1994: 6/8/9.9 NGK BP8H-N-10, 10/15 NGK BP8HS-15. 1995 and newer: 6/8 NGK BP8H-N-10, 9.9/10/15 NGK BP8HS-15. NGK BPZ8H-N-10 where radio interference suppression is required. Qty 2
Spark plug gapBP8H-N-10 engines (6/8, and 1994 9.9): 1.0 mm (0.040 in). BP8HS-15 engines (10/15, and 1995 and newer 9.9): 1.5 mm (0.060 in)
Spark plug torqueFinger tight then 1/4 turn, or 27 N·m (20 lb ft)
Idle speed (in gear)6: 650 ± 75 RPM; 8: 725 ± 50; 9.9 / 9.9 Sailpower: 725 ± 50; 10 Sea Pro / Marathon: 850 ± 50; XR / MAG / Viking 10: 725 ± 50; 15: 725 ± 50. Fast idle 1500 to 2000 RPM
Thermostat120° thermostat on the 9.9/10/15 and on the 6/8/Work 10 from 2000 and newer; the 6/8/Work 10 from 1999 and prior have no thermostat. Must begin to open 3 °C (5 °F) above the figure stamped on its bottom
AnodesOne aluminum anode on the gear case: replace if more than 50% consumed; never paint or coat it. Anode screw 3.4 N·m (30 lb in)
Propeller nut7.9 N·m (70 lb in) in the installation procedure

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: gear case oil, gear case plug gaskets

    Check: spark plugs, fuel filter, anodes

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

    Replace: gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, fuel filter, anodes

  3. Every 300 hours or 3 years

    Replace: gear case oil, gear case plug gaskets, water pump impeller

    Check: spark plugs, fuel filter, 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/Mariner 6/8/9.9/10/15 service manual, 90-827242R02, February 2003. 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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