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Mercury / Mariner 8 / 9.9 FourStroke (232 cc, carbureted, serial 0H000058 and above) service guide

Oil, gear oil, spark plugs and the service schedule for the Mercury / Mariner 8 / 9.9 FourStroke (232 cc, carbureted, serial 0H000058 and above) (8 to 9.9 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Mercury/Mariner 8 and 9.9 (4-Stroke), United States starting serial 0H000058; Model 9.9, and Model 8.0 and 9.9 Bodensee. 2 cylinder, over head camshaft, 232 cc (14.16 cu in), carbureted, reusable oil filter. A different engine from the 323 cc 9.9/15 (serial 0G590000 and above) and the 209 cc 8/9.9 (serial 0R042475 and above), which have their own sheets.

Quick answers

How much oil does a Mercury / Mariner 8 / 9.9 FourStroke take?
1 US quart (1 liter). it does not give separate with-filter and without-filter amounts.
What engine oil does a Mercury / Mariner 8 / 9.9 FourStroke use?
Quicksilver 4-Cycle Marine Oil, SAE 10W-30 for all temperatures; SAE 25W-40 may be used above 40 °F (4 °C). If not available, a premium 4-cycle engine oil meeting API SH, SG, SF, CF-4, CE, CD or CDII.
What gear oil does a Mercury / Mariner 8 / 9.9 FourStroke use, and how much?
Quicksilver Gear Lube Premium Blend. Quantity: Approximately 200 ml (6.8 US fl oz); Fill until lube flows out of the vent hole.
What spark plug does a Mercury / Mariner 8 / 9.9 FourStroke use?
NGK CR6HS, qty 2. Gap: 0.6 to 0.7 mm (0.024 to 0.028 in).
How often should a Mercury / Mariner 8 / 9.9 FourStroke be serviced?
The factory schedule lists: Every 100 hours of use or once yearly, whichever occurs first; Every 300 hours of use or three 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 8 / 9.9 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 / Mariner 8 / 9.9 FourStroke?
950 ± 50 rpm out of gear; trolling 850 ± 50 rpm. WOT: 8.0/9.9 Bodensee 5000 to 5500 rpm; 9.9 4500 to 5500 rpm.
What is the propeller nut torque on a Mercury / Mariner 8 / 9.9 FourStroke?
70 lb-in (7.9 Nm).

Maintenance specs

Engine oilQuicksilver 4-Cycle Marine Oil, SAE 10W-30 for all temperatures; SAE 25W-40 may be used above 40 °F (4 °C). If not available, a premium 4-cycle engine oil meeting API SH, SG, SF, CF-4, CE, CD or CDII
Engine oil quantity1 US quart (1 liter). it does not give separate with-filter and without-filter amounts
Oil filter (reusable)Reusable filter: wash and clean it in solvent at each oil change, replace it if damaged (cracked, torn, dented). Oil the O-ring seals and torque the filter to 70 lb-in (8 Nm)
Engine oil drain plug70 lb-in (8 Nm); lubricate the O-ring seal on the drain plug with oil. The plug is behind the drain plug access cover
Gear lubeQuicksilver Gear Lube Premium Blend
Gear lube quantityApproximately 200 ml (6.8 US fl oz); Fill until lube flows out of the vent hole
Gear lube plugs1 drain (fill) screw and 1 vent screw plug, each with a sealing washer, 60 lb-in (7.0 Nm); install new gaskets on the fill and vent screws
Gear case leak test pressure10 to 15 psi of air at the vent hole before filling; pressure should not drop for 15 seconds while applying a 2 to 3 pound force fore and aft to the top of the shift shaft
Spark plugNGK CR6HS, qty 2
Spark plug gap0.6 to 0.7 mm (0.024 to 0.028 in)
Spark plug torque9 lb-ft (12.3 Nm); or finger tight then 1/4 turn
Idle speed950 ± 50 rpm out of gear; trolling 850 ± 50 rpm. WOT: 8.0/9.9 Bodensee 5000 to 5500 rpm; 9.9 4500 to 5500 rpm
ThermostatAt 136 to 144 °F (58 to 62 °C) valve lift 0 (starts to open); above 158 °F (70 °C) valve lift minimum 0.12 in (3 mm). Thermostat bolts 70 lb-in (8 Nm)
AnodesGear housing anode screw 30 lb-in (3.5 Nm). Cylinder head anode bolt 13 lb-ft (18 Nm), with O-ring and anode plug
Propeller nut70 lb-in (7.9 Nm)
Valve clearance, coldIntake 0.15 to 0.20 mm (0.0059 to 0.0079 in); exhaust 0.20 to 0.25 mm (0.0079 to 0.0098 in). Cylinder head cover bolts 70 lb-in (8 Nm)

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 of use or once yearly, whichever occurs first

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

    Check: oil filter, spark plugs, fuel filter, anodes

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

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

    Check: oil filter, spark plugs, fuel filter, anodes

  3. Every 300 hours of use or three years

    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

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 8/9.9 service manual. 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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