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The Yanmar 4JH3-DTE 125HP inboard diesel engine is a four-cylinder marine diesel designed for pleasure-boat propulsion where a compact, mechanically controlled engine with turbocharged and intercooled performance is required. Yanmar rates the 4JH3-DTE at 91.9 kW / 125 mhp at 3,800 rpm from a 1.995-liter four-cylinder engine.
The 4JH3-DTE combines direct fuel injection, a Bosch distributor-type VE injection pump, turbocharging with intercooling, fresh-water cooling and a 12V 125A alternator. Yanmar lists a dry weight of 229 kg / 504.8 lb without gear and published dimensions of 1001.3 × 581 × 661 mm. The length figure includes the KM4A2 marine gear, so the final installation dimensions depend on the selected transmission and exhaust configuration.
Yanmar specifies the 4JH3-DTE at 91.9 kW / 125 mhp at 3,800 rpm. The manufacturer’s operation documentation also identifies a continuous rating of 85.3 kW / 116 hp at 3,700 rpm. These ratings are manufacturer test figures and should not be interpreted as a guaranteed boat speed.
Actual propulsion performance depends on hull design, vessel displacement, propeller diameter and pitch, marine-gear reduction ratio, shaft installation, loading and operating conditions. For a repower, the engine’s rated output should therefore be evaluated together with the complete propulsion system.
The 4JH3-DTE uses a 1.995-liter four-cylinder configuration with an 84 mm bore and 90 mm stroke. It is a vertical, water-cooled, four-stroke diesel engine intended for pleasure-boat applications in Yanmar’s technical documentation.
The engine’s relatively compact displacement is paired with forced induction rather than relying on a large naturally aspirated block. This allows the 4JH3-DTE to provide its specified 125 mhp output while retaining a four-cylinder marine-diesel configuration.
The Yanmar 4JH3-DTE is turbocharged and intercooled. Yanmar’s technical documentation identifies an IHI RHB52 water-cooled turbocharger on the engine. The intercooling system supports the engine’s forced-induction configuration and rated output.
Because the engine uses a turbocharger, exhaust routing, cooling-water connections, intake plumbing and service access should be planned carefully during installation or repowering. Use Yanmar’s installation documentation for the exact engine and marine-gear configuration.
The 4JH3-DTE uses direct fuel injection through a Bosch distributor-type VE injection pump. This is a mechanical fuel-system architecture rather than a modern electronically controlled common-rail system.
The injection pump, fuel lines and injectors should be serviced according to Yanmar’s specifications. Fuel quality and filtration are also important considerations for maintaining reliable operation of a mechanically injected marine diesel.
Yanmar specifies fresh-water cooling using a centrifugal fresh-water pump together with seawater cooling through a rubber-impeller seawater pump. The standard package includes an expansion tank for the fresh-water cooling system.
The cooling circuit must be installed correctly for the selected marine gear and exhaust arrangement. Seawater intake, strainer, pump, heat exchanger, hoses and exhaust mixing components should all be sized and routed according to the manufacturer’s installation requirements.
The current Yanmar specification lists a 12V 125A alternator for the 4JH3-DTE. The engine uses a 12V electric starting system, with Yanmar’s technical documentation specifying a 1.4 kW starter.
The 125A alternator can provide substantial charging capacity for a boat’s electrical system, but the complete charging installation still needs to account for battery-bank size, cable sizing, protection and the vessel’s actual electrical loads.
| Specification | Yanmar 4JH3-DTE |
|---|---|
| Engine configuration | In-line, 4-stroke, vertical, water-cooled diesel engine |
| Maximum rated output | 91.9 kW / 125 mhp at 3,800 rpm |
| Continuous rating | 85.3 kW / 116 hp at 3,700 rpm |
| Displacement | 1.995 L / 122 cu. in. |
| Cylinders | 4 |
| Bore × stroke | 84 × 90 mm / 3.31 × 3.54 in. |
| Combustion system | Direct injection |
| Fuel injection pump | Bosch distributor-type VE pump |
| Aspiration | Turbocharged and intercooled |
| Starting system | 12V electric starting, 1.4 kW starter |
| Cooling | Fresh-water cooling with seawater circuit |
| Alternator | 12V – 125A |
| Controls | Mechanical |
| Dry weight without gear | 229 kg / 504.8 lb |
| Published dimensions | 1001.3 × 581 × 661 mm |
| Standard panel | B20 |
| Mounting | Flexible rubber mounts |
| Certifications | RCD 1, BSO II, EMC, SOLAS |
Yanmar’s current 4JH3-DTE page states that the published length includes the KM4A2 marine gear. The manufacturer also provides technical drawings for configurations using other marine gears, including KMH4A1 and ZF25A.
The appropriate transmission and reduction ratio must be selected according to the boat, shaft system and propeller. A replacement engine should not be connected to an existing propeller system solely because the engine horsepower is similar; the gear ratio and installation geometry also need to be checked.
Yanmar lists the 4JH3-DTE at 1001.3 mm long × 581 mm wide × 661 mm high, with a dry weight of 229 kg / 504.8 lb without gear. Yanmar notes that dimensions can vary with different marine gears or exhaust elbows.
For repower projects, measure the complete engine bay before ordering. Check engine-bed mounting positions, shaft centerline, available height, exhaust clearance, service access, seawater plumbing, fuel connections and control-cable routing.
Yanmar’s standard engine package includes an L-type exhaust mixing elbow, 12V 125A alternator, B20 panel, flexible mounts, fresh-water expansion tank, electric stop solenoid and belt safety cover.
The precise supplied package should be confirmed with the engine configuration being purchased. Vessel-specific equipment such as shafting, propeller, fuel lines, exhaust hose and electrical installation may require separate components.
Yanmar lists optional equipment including a high-riser mixing elbow, C30 panel, 4 m, 6 m or 10 m extension harnesses, dual harness for a second station, TFX sidemount control head, glow air heater, trolling valve for the KMH4A marine gear and an onboard spare-parts kit.
Optional equipment should be matched to the selected transmission, control arrangement and vessel layout. Confirm compatibility before ordering accessories or modifying an existing installation.
The 125HP rating makes the 4JH3-DTE relevant to repower projects where the existing engine installation requires a four-cylinder diesel with forced induction. However, the correct repower decision depends on the boat manufacturer’s power range, engine-bed dimensions, transmission, propeller and shaft arrangement.
When replacing an older diesel, compare the old and new engines in detail rather than looking only at rated horsepower. Differences in engine weight, mounting position, gearbox ratio, exhaust height and shaft centerline can require additional installation work.
The 4JH3-DTE uses mechanical engine controls. Yanmar lists the B20 as the standard panel and the C30 as an optional panel. The B20 and C30 are Yanmar mechanical start/stop and tachometer panels designed for compatible mechanical Yanmar engines.
For installations requiring a remote control station, Yanmar lists extension harnesses, a dual harness for a second station and a TFX sidemount control head among the available options.
The 4JH3-DTE combines a mechanical fuel system with turbocharging, intercooling and fresh-water cooling. Routine maintenance therefore needs to cover the fuel system, lubrication system, cooling circuits, seawater pump, belts, exhaust components and turbocharger-related plumbing.
Yanmar’s operation manual specifies a forced lubrication system and provides engine and marine-gear service information. Use the manufacturer’s current documentation for lubricant specifications, service intervals, coolant requirements and inspection procedures rather than relying on generic diesel-engine schedules.
The Yanmar 4JH3-DTE 125HP combines a four-cylinder 1.995-liter diesel with direct injection, a Bosch VE pump, turbocharging and intercooling, mechanical controls and a 12V 125A alternator. Its 91.9 kW / 125 mhp rated output provides a higher-power option within Yanmar’s JH marine-diesel range.
For a new installation or repower, the most important checks are the vessel’s required power, engine-bay dimensions, engine-bed layout, marine gear, propeller and shaft system, cooling and exhaust arrangements, electrical system and control configuration.
Yanmar rates the 4JH3-DTE at 91.9 kW / 125 mhp at 3,800 rpm. Its documented continuous rating is 85.3 kW / 116 hp at 3,700 rpm.
The engine has four in-line cylinders and 1.995 liters of displacement.
Yes. The 4JH3-DTE is turbocharged and intercooled. Yanmar’s technical documentation identifies an IHI RHB52 water-cooled turbocharger.
The engine uses direct injection with a Bosch distributor-type VE pump. It is a mechanically controlled fuel system.
Yanmar lists a 12V 125A alternator. The engine’s starting system is also 12V, with a 1.4 kW starter specified in Yanmar’s technical documentation.
Yanmar lists a dry weight of 229 kg / 504.8 lb without gear. The installed propulsion package will weigh more after the selected marine gear and additional installation components are included.
Yanmar’s current specification states that the published engine length includes the KM4A2 marine gear. Yanmar also provides technical configurations for other compatible marine gears, so the exact gear should be selected for the vessel and propulsion system.
Yanmar’s current specification lists dimensions of approximately 1001.3 × 581 × 661 mm. Yanmar notes that dimensions can vary with different marine gears and exhaust elbows.
If you need a 125HP-class marine diesel engine for a suitable sailboat or pleasure-boat propulsion application, the Yanmar 4JH3-DTE provides four-cylinder diesel power with direct injection, turbocharging, intercooling, mechanical controls and a 12V 125A alternator.
Before purchasing, verify the vessel’s power requirement, engine-bay dimensions, mounting arrangement, marine gear, shaft and propeller configuration, exhaust system and control requirements. Buyers comparing Yanmar inboard diesel options can also review the Yanmar 3YM30AE 29.1HP, Yanmar 4JH110 110HP and Yanmar 4LV250 250HP inboard diesel engines.
Explore more inboard engines at Performance Engines.
