Mercury · Outboard

Mercury 9.9 FourStroke

The Mercury 9.9 FourStroke is a two-cylinder, 209.8 cc portable four-stroke, common on small fishing boats and tenders and as an auxiliary on small sailboats; the 8 hp version is the same engine and shares almost all service parts. From model year 2005 until early 2024 it was carburetted (serials 0R042475 to 1R279944); in June 2024 Mercury replaced it with an EFI engine of the same size (from serial 1R281445) that starts without a battery, still has no oil filter and, according to Mercury, needs no valve adjustment over its service life. Both generations come with a standard gearcase (2.08:1) or the larger Bigfoot gearcase, called Command Thrust from 2015, which has a 2.42:1 reduction and a bigger propeller for heavy boats and trolling and is always fitted to the ProKicker. The 9.9 EFI ProKicker sold before mid-2024 is a different 333 cc engine and is not covered here.

Manuals & documents
Wear parts & part numbers
Service intervals
Specifications
Good to know
On the marketplace

Manuals & documents

The links go to Mercury’s own documents — some as archived copies of pages the maker has since taken down. We host no manuals or drawings.

Operation, maintenance and installation manual 8/9.9 EFI FourStroke, Command Thrust and ProKicker (2025, 8M0235576) Operation manual servicelit.mercurymarine.com · PDF · EN
Operation manual 8/9.9 EFI FourStroke, Command Thrust and ProKicker (2025, 8M0238794, French) Operation manual servicelit.mercurymarine.com · PDF · FR
Operation manual 8/9.9 EFI FourStroke, Command Thrust and ProKicker (2025, 8M0238799, Spanish) Operation manual servicelit.mercurymarine.com · PDF · ES
Operation manual 8/9.9 EFI FourStroke, Command Thrust and ProKicker (2024, 8M0221312) Operation manual servicelit.mercurymarine.com · PDF · EN
Operation manual 8/9.9 FourStroke with carburettor, Command Thrust and ProKicker (2019, 8M0165091) Operation manual servicelit.mercurymarine.com · PDF · EN
Operation manual 8/9.9 FourStroke with carburettor, Command Thrust and ProKicker (2019, 8M0167445, French) Operation manual servicelit.mercurymarine.com · PDF · FR
Operation manual 8/9.9 FourStroke with carburettor, Command Thrust and ProKicker (2019, 8M0167450, Spanish) Operation manual servicelit.mercurymarine.com · PDF · ES
Operation manual 8/9.9 FourStroke with carburettor, Command Thrust and ProKicker (2016, 8M0116434) Operation manual servicelit.mercurymarine.com · PDF · EN
Operation manual 8/9.9 FourStroke with carburettor, Command Thrust and ProKicker (2015, 8M0108154) Operation manual servicelit.mercurymarine.com · PDF · EN
Operation manual 8/9.9 FourStroke with carburettor, BigFoot and ProKicker (2013, 8M0087056) Operation manual servicelit.mercurymarine.com · PDF · EN
Mercury literature portal: owner’s manuals by serial or model number (English, French, Spanish) Manual portal mnappsp.mercurymarine.com · EN
Brunswick publications: printed service manuals 892248R01 (carburetted) and 8M0239276 (6/8/9.9 EFI) Manual portal publications.brunswick.com · EN
Mercury press release: 8 and 9.9 hp EFI FourStroke and 9.9 hp EFI ProKicker (6 June 2024) Archived maker page web.archive.org · EN
Mercury FourStroke 2.5–20 hp product page with the 9.9 hp EFI specs (archived August 2025) Archived maker page web.archive.org · EN

Wear parts & part numbers

Part	OEM number	Also fits	Note
Service kit	`8M0120837`^1,2,3	—	Carburetted generation, standard gearcase, serial 0R042475 to 1R279944: fuel filter, oil drain seal, gearcase seals, thermostat with gaskets, two spark plugs, impeller kit and anode; oil and gear lube not included.
Service kit	`8M0120867`^4,5	—	Carburetted generation, Command Thrust (Bigfoot) gearcase, serial 0R042475 to 1R279944: same content as 8M0120837, but with the impeller kit for the larger gearcase.
Service kit	`8M0227353`^6,7,8	—	EFI generation, standard gearcase, serial 1R281445 on: fuel filter 8M0157133, oil drain washer 895146, two spark plugs 8M0204682, two anodes 875208, thermostat 8M0119207, impeller kit 803748K01, gearcase seal kit 8M0082880 and gasket 8M0214960.
Service kit	`8M0227355`^9,10	—	EFI generation with Command Thrust gearcase (ProKicker included), serial 1R281445 on: fuel filter, oil drain seal, gearcase seals, thermostat and gaskets, spark plugs, impeller kit and anodes.
Impeller kit (with gasket)	`803748K01`^11,12,13,7	—	Both generations, standard gearcase (also in the EFI 300 h kit): impeller, gaskets, roller pin, rubber grommet, plate and water tube. Quicksilver version: 803748Q01.
Impeller kit (with gasket)	`803748K02`^14,15,16	—	Carburetted generation with Bigfoot / Command Thrust gearcase (and ProKicker): impeller, seal, key, gasket, plate and water tube. Quicksilver version: 803748Q02. Dealers do not confirm it for EFI engines; for those, go by the 300 h kit 8M0227355.
Raw water pump impeller	`8M0214945`^11,17,18,19replaces 47-803748-1	—	Standard gearcase, carburetted generation, per the 2005-on parts diagram; for EFI engines, Mercury’s service kit lists the complete impeller kit 803748K01.
Raw water pump impeller	`8M0214944`^{14,20,21,22,23}replaces 47-803748	—	Bigfoot / Command Thrust gearcase and ProKicker, carburetted generation from serial 0R042475; the same impeller is used on the 20 hp four-stroke. Not confirmed for EFI engines.
Water pump repair kit	`803750A03`^11,24,25	—	Standard gearcase, listed from 2005 (carburetted generation); not confirmed for EFI engines. Housing, impeller, plate, water tube and gaskets: worth it when the housing or its liner is scored. The Bigfoot version 803750A06 is no longer available.
Spark plug	`8M0234113`^{26,7,29,30,28}replaces 8M0204682	NGK `DCPR6E`^26,27,28	Both generations, two per engine; NGK DCPR6E, gap 0.9 mm. 8M0204682 is the number in the EFI 300 h kit; the 2005 parts diagram listed 803507, no longer available.
Fuel filter (engine)	`8M0157133`^31,32,7,33replaces 35-16248	—	Both generations: in-line filter under the cowl, also in the EFI 300 h kit.
Thermostat	`8M0119207`^7,34	—	EFI generation (in its 300 h kit); dealers list it for 8–30 hp four-strokes. The 2005 diagram for carburetted engines shows 855676002 / 855676005, no longer available, and no dealer confirms 8M0119207 as their replacement.
Thermostat gasket	`8M0214960`^35,7	—	Both generations (8 and 9.9 hp, 209 cc); in the EFI 300 h kit.
Anode (lower unit)	`853762T01`^11,14,36,37	—	Trim tab anode on the gearcase. Carburetted generation, standard, Bigfoot and Command Thrust gearcase (both 2005-on diagrams); not confirmed for EFI engines, whose 300 h kit has two 875208 anodes instead.
Anode (engine)	`875208`^7,38,39	—	EFI generation from serial 1R281445: two in the 300 h kit; dealers sell it for Mercury/Mariner 4–9.9 hp. Where the two sit on the engine is not shown in an official diagram.
Drain plug gasket	`895146`^40,7	—	Both generations: sealing washer under the oil drain bolt 895136 (2005-on diagram), also in the EFI 300 h kit.
Gear oil plug gaskets	`8M0082880`^41,7,11	—	Both generations (from serial 0R008146): blue seal washers for the gear lube fill/drain and vent plugs, also in the EFI 300 h kit. The 2005 diagram showed gasket 95220, no longer available.
Timing belt	`895120`^42,43,44	—	Carburetted generation, from 2005 (camshaft diagram); not confirmed for the EFI engine. Dealer job.
Gear oil	`858058K01`^10,38,26	—	Mercury Premium gear lube (80W-90), 946 ml bottle, enough for two to three changes. Dealers list it for the EFI generation; the manual allows Premium or High Performance gear lube.
Propeller shaft grease	`92-802859A1`²⁶	—	Mercury 2-4-C with PTFE, named in the EFI manual for the propeller shaft, swivel bracket, tilt tube and clamp screws; alternative: Extreme Grease 8M0190472.

Numbers checked against the sources below on 12 October 2026. Always confirm against your serial number and exact type before ordering.

Service intervals

Task	Interval
Oil level check	Before every outing: oil on the dipstick (engine upright), lanyard stop switch, fuel lines, propeller and steering²⁶
Fresh-water wash	After every use in salt, brackish, muddy or polluted water, with the engine running so the thermostat opens²⁶
Engine oil change	Every 100 h or yearly; EFI manual: every 100 h or before long-term storage. More often with a lot of trolling. No oil filter^27,26
Gear oil change	Every 100 h or yearly²⁷
Anode	Check every 100 h or yearly, more often in salt water; replace before it is fully eroded, never paint it²⁶
Lubrication	Every 100 h or yearly: swivel bracket, tilt tube, clamp screws, tiller linkage and propeller shaft²⁶
Fuel filter	Replace the low-pressure filters on the suction side every 100 h or yearly (dealer); inspect the in-line filter at every service²⁶
Thermostat	Inspect every 100 h or yearly when used in salt or brackish water (dealer)²⁶
Spark plug	Replace every 300 h or 3 years; anti-seize on the threads every 100 h. Manuals before 2016: replace after the first 100 h or first year, then inspect every 100 h²⁶
Raw water impeller	Replace every 300 h or 3 years (dealer), sooner if the tell-tale stream weakens or the engine overheats²⁶
Timing belt	EFI: inspect every 300 h or 3 years (dealer); manuals up to 2015: every 100 h or yearly²⁶
Valve clearance	Carburetted engines: check every 100 h or yearly per the 2013 and 2015 manuals (dealer); EFI engine: no adjustment needed according to Mercury^45,46
Full service	At the dealer’s 300 h / 3-year service, also check wiring connectors, remote cable adjustment, power tilt fluid and engine mounts²⁶

Hours or years, whichever comes first. The schedule follows Mercury’s operation manuals 8M0235576 (EFI, 2025) and, for the carburetted generation, 8M0165091 (2019) and 8M0108154 (2015). “Dealer” marks the jobs Mercury leaves to a dealer. Running-in: for the first 2 hours vary the throttle up to 4500 rpm and avoid long idling; for the next 8 hours, no more than 5 minutes at a time at full throttle.

Specifications

Cylinders	2 in line, four-stroke, camshaft driven by a toothed belt²⁶
Displacement	209.8 cc (12.8 cu in), both generations^27,26
Bore × stroke	55 × 44 mm^27,26
Power	7.3 kW (9.9 hp); 8 hp version: 5.9 kW²⁶
Full-throttle range	5000–6000 rpm²⁶
Idle speed	In forward gear: 900–1000 rpm (EFI), 900 rpm (carburetted)²⁶
Injection	Carburettor until early 2024; from June 2024 electronic fuel injection that starts without a battery⁴⁷
Valve clearance (cold)	Intake 0.13–0.17 mm, exhaust 0.18–0.22 mm; on the EFI engine Mercury says no adjustment is needed in its service life⁴⁶
Spark plug	NGK DCPR6E (2), gap 0.9 mm (2013 manual: 0.8–0.9 mm); 27 N·m (20 lb-ft) or finger-tight plus 1/4 turn^26,48
Gear ratio	2.08:1 standard gearcase; 2.42:1 Command Thrust (Bigfoot) and ProKicker²⁶
Engine oil capacity	approx. 0.8 l (27 US fl oz); drain plug only, no oil filter²⁶
Engine oil grade	NMMA FC-W SAE 10W-30 (mineral or semi-synthetic) for all temperatures; SAE 25W-40 FC-W above 4 °C; fully synthetic oil not recommended²⁶
Gear oil capacity	approx. 320 ml (10.8 US fl oz) standard gearcase; 370 ml (12.5 US fl oz) Command Thrust / ProKicker²⁶
Gear oil grade	Mercury/Quicksilver Premium or High Performance gear lube²⁶
Fuel	Unleaded petrol, at least RON 91 (USA/Canada: 87 AKI); up to 10 % ethanol²⁶
Dry weight	EFI generation: from 38.5 kg (85 lb) for the lightest model, 45.5 kg (100 lb) with Command Thrust⁴⁹
Alternator	12 A (145 W) on the electric-start EFI models⁴⁹
Battery	Electric start: 465 MCA or 350 CCA²⁶
Shaft length	15 in (MH, EH), 20 in (MLH, ELH), 25 in (XL; in the EFI range only with Command Thrust / ProKicker)⁵⁰
Years built	Carburetted: model year 2005 to early 2024 (serial 0R042475–1R279944); EFI: from June 2024 (serial 1R281445 on), in production^47,1,6

Good to know

Read the serial number on the transom bracket before buying service parts: up to 1R279944 it is the carburetted generation, from 1R281445 the EFI one, and the 300-hour kits differ (8M0120837 / 8M0120867 versus 8M0227353 / 8M0227355).⁶
Check whether your gearcase is the standard one or Command Thrust / Bigfoot, the larger one with 2.42:1 reduction and a bigger propeller that every ProKicker has. Impellers and impeller kits differ: 803748K01 for the standard gearcase, 803748K02 for the larger one (carburetted generation).¹⁴
There is no oil filter. Drain through the plug with the motor tilted up, lower it for a minute and tilt it again so trapped oil runs out; refill with only about 800 ml and read the dipstick with the engine upright. Do not suck the oil out through the dipstick tube.²⁶
Watch the tell-tale stream every time you start. A weak or missing stream means a blocked outlet or a tired impeller, especially after the motor has stood for a season.²⁶
Fill gear lube from the bottom plug until it appears at the upper vent, and fit new blue seal washers (8M0082880). Milky oil means water is getting past a seal.²⁶
A used “Mercury 9.9 ProKicker EFI” from before mid-2024 is a different 333 cc engine on the 15/20 hp platform; not all parts on this page fit it.⁵¹

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Sources

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