Yanmar 2GM20F – Inboard diesel
Photo: PHGCOM, CC BY-SA 3.0, via Wikimedia Commons

Yanmar · Inboard diesel

Yanmar 2GM20F

The 2GM20F is the two-cylinder, 0.64-litre indirect-injection diesel of Yanmar’s GM series, rated at about 18 hp — an up-rated 2GM and one of the most common auxiliaries in small and mid-size sailing yachts. The F marks the fresh-water-cooled version with heat exchanger; the plain 2GM20 is cooled directly with seawater and takes a different impeller, thermostat and anodes. Engines built in Japan (serial without ‘E’, until about 1996/97) and the European-assembled ‘YEU’ engines (serial starting with ‘E’, until 2004) use different raw water pumps and service kits. The YM series (2YM15, 3YM20) replaced it.

Manuals & documents

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

Wear parts & part numbers

PartOEM numberAlso fitsNote
Raw water pump impeller124223-420921,2,3Sierra 18-89501Japanese-built 2GM20F (serial without ‘E’): keyed impeller, paper gasket, cover plate approx. 70 mm. Not for YEU engines or the seawater-cooled 2GM20.
Pump cover gasket124223-421104,2—Goes with impeller 124223-42092 (Japanese-built F).
Impeller kit (with gasket)128990-425705,6,7replaces 128990-42200—European-built YEU engines (serial starting with ‘E’, about 1996/97–2004): pin-drive impeller, O-ring-sealed cover approx. 75 mm.
Pump cover O-ringX0506597-018,9—YEU engines (serial ‘E’); service kits list it as X0506597.
Raw water pump impeller104211-4207110,11replaces 104211-42070—Seawater-cooled 2GM20 only (Japanese-built): small 6-blade impeller, approx. 40 mm, pump with 58 mm cover plate. Does not fit the 2GM20F.
Pump cover gasket104211-4209012—Seawater-cooled 2GM20, with impeller 104211-42071 (one source).
Engine oil filter119305-3517013,14,2replaces 119305-35151replaces 119660-35150—All 2GM20/2GM20F. The current filter is shorter than the original but is Yanmar’s approved replacement.
Fuel filter (engine)104500-5571016,17,18Hengst E486KP-D45215Engine-mounted element, all versions incl. YEU.
Fuel filter O-ring24341-00044019,2—Renew with every fuel filter element.
Air filter128270-1254020,21—Intake silencer element, all versions.
Alternator V-belt25132-00370022,23,24—F version incl. YEU (960 × 13 mm); the seawater-cooled 2GM20 uses another belt.
Seawater pump belt104511-7878025,26,27—The separate small belt that drives the raw water pump (marked M-19); 2GM20 and 2GM20F.
Thermostat121750-4980028,29,30—F version incl. YEU, opens at 71 °C. The seawater-cooled 2GM20 uses another thermostat.
Anode (engine)27210-20030031,32—Pencil zinc, seawater-cooled 2GM20 only: one in the side of the block, one at the rear of the head. Not listed for the F.
Anode plug gasket123210-0931033,32—One per anode.
Service kitSK-MARINE-00334,35,2—Genuine Yanmar kit for the Japanese-built 2GM20F (also sold as SK-MARINE-003-G): oil filter, fuel filter + O-ring, impeller 124223-42092 + gasket.
Service kitSK-MARINE-0059,36,37—Genuine Yanmar kit for YEU engines (serial ‘E’; also the YM series): oil filter, fuel filter + O-ring, impeller 128990-42200 and its O-rings.
Gasket set728271-9260538—2GM20 and 2GM20F (one dealer).

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

Service intervals

TaskInterval
Full serviceAt least yearly: engine oil and filter, fuel filter element, impeller (dealer guideline)39
Raw water impellerYearly (dealer guideline)6
Fuel filterYearly (dealer guideline)15
Air filterEvery 2 years (dealer guideline)21
Seawater pump beltEvery 2 years (dealer guideline)40

Yanmar does not publish the GM-series operation manual online, so there is no official schedule here — these are dealer guidelines. The hour-based intervals are in the manual, which a Yanmar dealer can supply.

Specifications

Cylinders2, in-line, four-stroke41
Displacement0.636 l (75 × 72 mm)41
CombustionIndirect injection (swirl pre-chamber)42
Power18.2 hp at 3,600 rpm (max.); 16.0 hp at 3,400 rpm (continuous)41
Cooling2GM20F: fresh-water cooling with heat exchanger; 2GM20: direct seawater cooling41
Engine oil capacityapprox. 2.0 l (dealer data sheet; fill to the dipstick mark)42
Engine oil gradeAPI CD, SAE 15W-4042
Valve clearance (cold)0.2 mm intake and exhaust42
Injection pressure170 ± 5 kgf/cm² (approx. 167 bar)42
Injection timing15° BTDC42
Thermostat opens at71 °C28
Starter motor12 V, 1.0 kW42
Alternator12 V; 35 A per Yanmar Australia, 55 A (Hitachi LR155-20) per dealer data — check the label on yours43,42
Dry weight114 kg (2GM20F); 106 kg (2GM20); 125 kg (2GM20FV)41
GearboxYanmar KM2P; V-drive versions KM3V41
SaildriveC versions (2GM20FC): Yanmar SD2042
Years builtc. 1984 – c. 200442,43
SuccessorYanmar 2YM15 / 3YM2043

Good to know

  • Check the serial number before ordering an impeller or service kit: a serial starting with ‘E’ means a European-assembled YEU engine (about 1996–2004) with a different raw water pump — O-ring cover, pin-drive impeller, kit SK-MARINE-005. Earlier Japanese-built engines take SK-MARINE-003.9
  • If in doubt, measure the pump cover plate: about 70 mm on Japanese-built 2GM20F pumps, about 75 mm on YEU pumps. Japanese pumps have hose tails screwed in, YEU pumps have them cast in.44
  • The seawater-cooled 2GM20 (no F) has a smaller pump with a 58 mm cover plate and a different impeller — 2GM20 and 2GM20F impellers are not interchangeable.39
  • The raw water pump has its own small V-belt (104511-78780), separate from the alternator belt. If it slips or breaks, the cooling water stops — check it at every service and carry a spare of both belts.25
  • On the seawater-cooled 2GM20, check both pencil zincs (side of the block and rear of the head) and fit new ones with new gaskets once they are half gone.32

Videos & how-tos

Links to YouTube, nothing embedded. The maker’s own channel comes first; the rest are channels we found clear and correct for this model.

Fitted in

Boats whose builder lists it as standard or optional equipment:

  • Contessa 32 — Yanmar 2GM 18 hp (Yard specifications 2004 and 2010: one of two engine choices, two cylinders, 18 hp, cooled directly by sea water, two-blade fixed propeller on a conventional shaft)

On the marketplace

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Sources

  1. wholesalemarine.com/sierra-18-8950-impeller/
  2. shop.tnorrismarine.co.uk/products/service-kit-for-yanmar-2gm20f-3gm30f-2gmf-3gmf-service-…
  3. ess-kayyards.com/products/124223-42092-yanmar-impeller-gmf-series-replaces-128296-42070-u…
  4. dieselpartsdirect.com/ym12422342110
  5. dieselpartsdirect.com/ym12899042570
  6. svb24.com/en/impeller-for-yanmar-2-3ym-series-2-3-gm20-30-f-yeu-vetus-m2-3-4-series.html
  7. discountmarinesource.com/store/index.php?route=product/product&product_id=95822
  8. dieselpartsdirect.com/ymx050659701
  9. marine-power.co.uk/sk-marine-005-service-kit-2gm-3gm-2ym-3ym
  10. dieselpartsdirect.com/ym10421142071
  11. svb24.com/en/impeller-for-yanmar-2gm20-3gm30-2qm15.html
  12. dieselpartsdirect.com/ym10421142090
  13. dieselpartsdirect.com/ym11930535170
  14. seafarerstore.com/products/yanmar-119305-35170-oil-filter-replaces-119305-35151-for-ym-an…
  15. svb24.com/en/hengst-diesel-filter-for-yanmar-1-2-3-gm-series-ysm-7-12-ps-2-qm-15-20-30-an…
  16. dieselpartsdirect.com/ym1045005571012
  17. foghboatsupplies.com/fuel-filter.html
  18. marineengineparts.com/yanmar-104500-55710-filter-fuel/
  19. dieselpartsdirect.com/ym24341000440
  20. dieselpartsdirect.com/ym12827012540
  21. svb24.com/en/air-filter-for-yanmar-2-3-gm-2-3-ym.html
  22. dieselpartsdirect.com/ym25132003700
  23. svb24.com/en/v-belt-for-yanmar-2gm20f-3gm30f.html
  24. parts4engines.com/products/yanmar-2gm20-f-alternator-belt
  25. dieselpartsdirect.com/ym10451178780
  26. marineengineparts.com/yanmar-104511-78780-belt/
  27. thedockshoppe.com/yanmar-water-pump-belt-2gm3gm-10451178780.html
  28. dieselpartsdirect.com/ym12175049800
  29. svb24.com/en/p/thermostat-for-yanmar-2gm-2gm20-3gm-3gm20-3hm.html
  30. discountmarinesource.com/store/index.php?route=product/product&product_id=95141
  31. dieselpartsdirect.com/ym27210200300
  32. dedieseldokter.nl/a-67722139/yanmar-2gm20-yanmar-2gm20f-onderdelen/yanmar-2gm20-anode-set…
  33. dieselpartsdirect.com/ym12321009310
  34. bottomlinemarine.com/prod_cat/P_yanmar-engine-service-kit--2gm20f-3gm30f-2gmf-3gmf--yeuse…
  35. riggingshoppe.com/products/yanmar-maintenance-kit-2gmf-2gm20f-3gmf-3gm30f
  36. frenchmarine.com/product/Yanmar-SK-Marine-005-G-Marine-Service-Kit-2GM20-F-YEU-2GM20-F-YE…
  37. shop.tnorrismarine.co.uk/products/sk-marine-005-g-service-kit-for-yanmar-2ym15-3ym20-3ym3…
  38. dedieseldokter.nl/en_GB/a-64732974/yanmar-2gm20-and-yanmar-2gm20f-parts/yanmar-2gm20-yanm…
  39. parts4engines.com/products/yanmar-2gm20-annual-service-kit
  40. svb24.com/en/yanmar-v-belt-for-2-3-gm-ym-series-3hm-series-seawater-pump.html
  41. web.archive.org/web/20031226022632/http://www.yanmar.com.au:80/marine/gm_series/gm_series…
  42. lsm-diesel.dk/2012/yanmar/tekniskdata_dk/2gm20tekniskdata.htm
  43. web.archive.org/web/20080719185946/http://www.yanmar.com.au/marine/gm_series/gm_series.htm
  44. parts4engines.com/products/yanmar-2gm20f-raw-water-pump-impeller-service-rebuild-kits-1

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