Yanmar 3JH40
40 HP · Freshwater (heat exchanger) cooled, with raw-water circuit
The Yanmar 3JH40 (3JH40) is a 3-cylinder naturally aspirated marine diesel and the common-rail successor to the long-serving 3JH4E. Yanmar markets it as the world’s smallest common-rail inboard marine diesel by displacement, size and weight, and it is a standard fit on production cruising sailboats and catamarans up to about 45 ft — boats like the Lagoon 42, Beneteau Oceanis, Dufour and Hanse ranges — used singly or as a twin-engine pair. It uses electronically-managed Bosch common-rail direct injection, freshwater (heat-exchanger) cooling, and is commonly paired with a KM35A marine gear or an SD60 saildrive. Below are its published specifications, the maintenance schedule, and the genuine Yanmar service-part numbers.
Specifications
| Engine type | 3-cylinder, in-line, naturally aspirated, direct injection |
|---|---|
| Fuel system | Bosch common rail, electronically managed |
| Displacement | 1.642 L (100 cu in) |
| Bore × stroke | 88 × 90 mm (3.46 × 3.54 in) |
| Maximum output | 40 mhp (29.4 kW) @ 3000 rpm |
| Low idle speed | 800 rpm |
| Aspiration | Natural aspiration |
| Fuel | Diesel |
| Cooling | Freshwater cooling (centrifugal pump + heat exchanger); raw-water circuit by rubber-impeller pump |
| Engine oil specification | API CD or higher, SAE 10W-30 or 15W-40 |
| Starting system | Electric, 12V – 1.4 kW starter |
| Alternator | Valeo 12V – 125A |
| Controls | Mechanical cable (standard); VC10 electronic control optional |
| Direction of rotation | Counterclockwise viewed from stern |
| Marine gear / drive | KM35A marine gear, or SD60 saildrive |
| Dry weight (without gear) | 192 kg (423 lb) |
| Dimensions (L × W × H, with gear) | 774 × 580 × 632 mm |
| Emissions | EPA Tier 3 · EU RCD 2 · BSO II |
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 expansion tank
- Drain any water from the fuel pre-filter / water separator
- Check the V-ribbed 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 marine-gear / saildrive oil (see the separate gear manual)
- Re-check and adjust the V-ribbed belt tension
- Re-check 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 on-engine fuel filter element
- Replace the fuel pre-filter / water-separator element
- Inspect the seawater pump impeller and replace it if worn
- Check and adjust the V-ribbed belt tension
- Clean the raw-water strainer
Every 1000 hours, or as the operation manual specifies
- Replace the seawater pump impeller
- Check and adjust the intake / exhaust valve clearance
- Replace the engine coolant (long-life antifreeze)
- Have a Yanmar dealer check the common-rail injectors and high-pressure fuel system
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) | 119305-35170 Spin-on oil filter. Same filter Yanmar uses across much of the small marine range. |
|---|---|
| Fuel pre-filter / water-separator element | 121857-55710 Element for the supplied fuel pre-filter with water separator (fitted ahead of the on-engine filter). Drain its water bowl daily and replace the element at the annual / 250-hour service. |
| On-engine fuel filter element | 129A00-55800 The fine fuel filter element on the engine. Common-rail systems are intolerant of dirty fuel and water — keep both this and the pre-filter on schedule, and bleed the system after changing. |
| Seawater pump impeller kit | 129670-42610 ≈ Speedseal / Sierra equivalents available Current Yanmar impeller kit (supersedes 129670-42531 / 129670-42530); threaded for an internal puller. Cover O-ring is 119773-42570. Also shared with the 4JH45 / 4JH110 / 3JH5AE. |
| V-ribbed (multi) drive belt | 129675-42280 Drives the freshwater pump and alternator. Check tension at each service; replace if cracked or glazed. |
What owners watch
Clean fuel is non-negotiable on a common-rail engine
Unlike the older mechanical-injection Yanmars, the 3JH40 runs a high-pressure Bosch common-rail system that is far less tolerant of water and dirt. The supplied pre-filter / water separator is the engine’s first line of defence — drain its bowl often and keep both fuel elements on schedule. Most CR fuel-system trouble traces back to neglected filtration.
Seawater impeller
The impeller is the usual raw-water-cooling weak point — a shredded impeller overheats the engine quickly. Inspect it at the annual service even though replacement falls on the longer-hours interval, carry a spare (129670-42610), and note it is threaded for an internal puller, so the right tool makes the job far easier.
Electronic engine management
The 3JH40 is electronically managed and reports faults through the Yanmar display panel as diagnostic codes. A fault code points you to the system at issue rather than leaving you guessing — note the code before clearing it, and a Yanmar dealer can read deeper data if needed.
Mixing elbow and exhaust
As on any marine diesel, the exhaust mixing elbow carbons up and corrodes over time and is worth periodic inspection. Yanmar offers a high-riser mixing elbow option in place of the standard L-elbow where the installation geometry calls for it.
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.
Download the JH-series Operation Manual and parts catalogue from Yanmar’s support / manuals portal, and confirm parts and intervals against your engine’s serial number.
Never miss a Yanmar 3JH40 service
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Track your Yanmar 3JH40 →Specifications are summarised from Yanmar’s published 3JH40 datasheet (DS_3JH40_A4_022021) and the JH-series Operation Manual (0AJHM); service-part numbers are from Yanmar’s genuine 3JH40 service kit (SK-JH40-001). Figures are for reference only, the 3JH40 is electronically managed and several service points should be carried out by a Yanmar dealer, and fluid capacities and valve clearances vary by configuration. Always confirm against your engine’s own operation manual and serial number before ordering parts or carrying out service.