Yanmar 3GM30F
27 HP · Heat exchanger (freshwater / indirect) cooled
The Yanmar 3GM30F (3GM30F) is a 3-cylinder naturally aspirated marine diesel from Yanmar’s GM series — probably the single most common auxiliary engine on 30–38 ft cruising sailboats of its era, fitted to boats like the Catalina 320 and many Beneteau, Catalina and Hunter models from the mid-1980s to mid-2000s. The "F" means it is the freshwater (heat-exchanger) cooled version. It uses indirect injection through a swirl-type pre-combustion chamber, and shares its maintenance schedule and most service parts with the 2-cylinder 2GM20F. Below are its published specifications, the maintenance schedule, and the genuine Yanmar service-part numbers.
Specifications
| Engine type | 3-cylinder, in-line, naturally aspirated, indirect injection |
|---|---|
| Combustion system | Swirl-type pre-combustion chamber (indirect injection) |
| Displacement | 0.954 L (58.22 cu in) |
| Bore × stroke | 75 × 72 mm (2.95 × 2.83 in) |
| Compression ratio | 23.0 : 1 |
| Continuous output | 24 HP (18 kW) @ 3400 rpm |
| Maximum output (1-hour rating) | 27 HP (20 kW) @ 3600 rpm |
| Aspiration | Natural aspiration |
| Fuel | Diesel |
| Fuel-injection timing | 18° ± 1° BTDC |
| Cooling | Freshwater cooling with heat exchanger |
| Valve clearance (cold) | 0.2 mm (0.008 in), intake and exhaust |
| Engine oil capacity | 2.6 L (≈ 2.75 US qt) |
| Starting system | Electric, 12V – 1.0 kW starter |
| Alternator | 12V – 55A |
| Direction of rotation | Counterclockwise viewed from stern |
| Standard gearbox | KM2P constant-mesh (2.62 : 1) · KM3P optional |
| Dry weight (with KM2P) | 137 kg (302 lb) |
Maintenance schedule
Yanmar's recommended service intervals for this engine. Most items are time-or-hours, whichever comes first — boats that sit still hit the calendar interval long before the hours.
Daily, before starting and after running
- Check the engine oil level on the dipstick
- Check the coolant level in the heat-exchanger header tank
- Check the fuel level and drain any water from the fuel filter / separator
- Check the alternator drive-belt tension
- Confirm the seawater seacock is open and the raw-water strainer is clear
- Look over the engine for fuel, oil or coolant leaks
- After starting, confirm cooling water is discharging at the exhaust outlet
After the first 50 hours (running-in)
- Change the engine oil
- Change the engine oil filter
- Change the gearbox / saildrive oil (see the separate gear manual)
- Re-check and adjust the alternator drive-belt tension
- Re-check external nuts, bolts and the flexible engine-mount fastenings
Every 250 hours or once a year, whichever comes first
- Change the engine oil
- Change the engine oil filter
- Replace the fuel filter element and bleed the fuel system
- Inspect the raw-water pump impeller and replace it if worn or cracked
- Replace the heat-exchanger sacrificial zinc anode
- Check and adjust the intake and exhaust valve clearance to 0.2 mm (cold)
- Check and adjust the alternator and seawater-pump belt tension
- Clean the raw-water strainer
- Inspect the heat exchanger and clean the tube stack if cooling is down
Every 2 years
- Replace the engine coolant (long-life antifreeze, correctly mixed)
- Replace the fuel hoses and the seawater hoses
Every 1000 hours (have a Yanmar dealer carry these out)
- Check the fuel-injection nozzle spray pattern and injection pressure
- Inspect the fuel-injection pump
- Inspect the intake/exhaust valve seats and lapping
Genuine service parts
Yanmar part numbers for the routine service items on this engine. Several vary by build date or cooling type — check the note before ordering. Genuine parts are stocked by the Yanmar dealer network; where a cross-reference is shown, an aftermarket equivalent is also available.
| Engine oil filter (spin-on) | 119305-35151 / 119305-35170 Spin-on filter fitted to the whole GM/HM range. Yanmar lists 119305-35151 as the current genuine number; 119305-35170 is the long-running equivalent and is what most chandlers stock. Either fits. |
|---|---|
| Fuel filter element (on-engine) | 104500-55710 The element in the on-engine fuel filter. Bleed the fuel system after changing it. Most boats also run a primary Racor-type separator ahead of this — service that separately. |
| Raw-water pump impeller | 128296-42070 ≈ Johnson 09-810B · Sierra 18-8950 Fits Japanese-built freshwater-cooled 2GM20F / 3GM30F from 1983 to 2005 (supersedes 124223-42091 / 124223-42092). It does NOT fit 1997-and-later European-built engines (serial number begins with "E"), which use a different pump and impeller. Renew the cover gasket (124223-42110) and O-ring (24341-000440) when you change it. |
| Heat-exchanger sacrificial zinc anode | 27210-200300 ≈ Martyr CMZ / CDZ 9-001 Pencil anode (30 mm x 20 mm, M8 thread) in the heat exchanger. Replace at least annually — more often in warm or brackish water. The raw-water-cooled GM models (no "F") have no heat exchanger and so no engine anode. |
| Air-cleaner element | 128270-12540 GM air-cleaner element. Clean periodically and replace when it is damaged or heavily fouled rather than on a fixed hour interval. |
| Alternator drive belt | 25132-003700 V-belt driving the alternator. Check tension at every service and replace if it is cracked or glazed. Belt size can vary if a higher-output alternator has been fitted — confirm against your installation. |
| Seawater-pump belt ("M/19") | 104511-78780 Separate small belt driving the engine-mounted seawater pump on the GM range. Inspect with the alternator belt and replace if worn — a failed seawater-pump belt stops raw-water flow and overheats the engine. |
What owners watch
Exhaust mixing elbow
The exhaust mixing elbow is the classic GM-series weak point. Carbon and salt build up inside it and the casting corrodes from the wet exhaust, gradually choking off flow. A restricted elbow causes overheating and, if it fails, can let water back toward the cylinders. Pull and inspect it periodically — many owners simply plan to replace it every few years rather than wait for symptoms.
Raw-water impeller
The impeller is on the annual / 250-hour list, but it is worth inspecting more often — a shredded impeller can overheat the engine within minutes. Carry a spare (128296-42070) and confirm whether your engine is Japanese or European built before ordering, because the European units take a different impeller.
Fuel cleanliness and the water separator
Draining water from the fuel filter is a daily-use habit. On a boat that sits, water and "diesel bug" accumulate, and a watered or clogged filter is the most common no-start or power-loss cause on these engines. A primary Racor-type separator ahead of the on-engine filter is cheap insurance.
Heat-exchanger zinc and scaling
Replace the pencil zinc (27210-200300) at least once a year; a wasted anode lets the heat-exchanger tube stack corrode. If running temperatures creep up, the tube stack may be scaled and need cleaning. (Raw-water-cooled GM engines have no heat exchanger or engine zinc to service.)
Valve clearance
The GM is a simple overhead-valve engine with a 0.2 mm cold valve clearance. Noisy tappets or slightly rough running are often just clearances drifting out of adjustment — set them at the 250-hour service rather than chasing bigger problems first.
Manufacturer documentation
The figures above are summarised for quick reference. For the full operator's manual and illustrated parts list, go straight to Yanmar — they keep the current revision, so you always get the right version for your engine.
The GM series is discontinued. Download the 1GM/2GM/3GM Operation Manual (128270) and the genuine parts catalogue from Yanmar’s support / manuals portal, and confirm parts against your engine’s serial number.
Other engines in this range
Never miss a Yanmar 3GM30F service
Keeply builds your engine's maintenance schedule, tracks the hours, and reminds you before a service is due. Ask First Mate "what's overdue?" and get an answer from your own records. Free to start, no credit card.
Track your Yanmar 3GM30F →Specifications are summarised from Yanmar’s published GM-series technical data (datasheet 60A123GM) and the 1GM10/2GM20(F)/3GM30(F)/3HM35(F) Operation Manual (128270-4E); service-part numbers are cross-referenced from Yanmar genuine-parts listings. Figures are for reference only — the GM range was built from 1983 to 2005 in both Japanese and European (serial prefix "E") variants with some differing parts, and raw-water vs freshwater cooling changes several items. Always confirm against your engine’s own operation manual and serial number before ordering parts or carrying out service.