The Weichai M21 series is a marine diesel engine family designed for main propulsion applications. The series includes the 6M21 inline-six and 8M21 V8 configurations, covering a power range of 599–1000 kW at 2300 rpm in the MGO-fueled model range.
The 6M21 has a displacement of 12.54 L, while the 8M21 has a displacement of 16.72 L. Both use a 2200 bar high-pressure common rail fuel system, along with turbocharging and intercooling. Key specifications include a minimum specific fuel consumption of 204 g/kW·h, oil consumption of no more than 0.3 g/kW·h, and a torque reserve of 15–30%.
With its high power output, electronically controlled fuel system and marine-focused configuration, the M21 series is suitable for a range of propulsion applications requiring reliable power at 2300 rpm.
What Is the Weichai M21 Marine Engine Series?
The M21 is part of the Weichai marine propulsion engine range and is available in two main configurations: the 6M21 inline-six and the 8M21 V8.
Both configurations use a four-stroke, water-cooled design with a 127 × 165 mm bore and stroke. The series combines turbocharging and intercooling with electronically controlled high-pressure common rail fuel injection.
The M21 series is designed to provide high power output in a relatively compact package for marine propulsion. Major components, including the engine block, cylinder head and crankshaft, use high-strength designs. The engine family also completed 2,000 hours of endurance testing during its development.
What Are the Main Specifications of the Weichai M21?
The M21 series includes two primary engine configurations with different displacement and power ranges.
| Parameter | 6M21 | 8M21 |
|---|---|---|
| Configuration | Inline 6-cylinder, four-stroke | V8, four-stroke |
| Displacement | 12.54 L | 16.72 L |
| Bore × Stroke | 127 × 165 mm | 127 × 165 mm |
| Aspiration | Turbocharged and intercooled | Turbocharged and intercooled |
| Fuel System | 2200 bar common rail | 2200 bar common rail |
| Fuel | MGO | MGO |
| Power Range | 599–735 kW | 735–1000 kW |
| Rated Speed | 2300 rpm | 2300 rpm |
| Minimum Fuel Consumption | 204 g/kW·h | 204 g/kW·h |
| Oil Consumption | ≤0.3 g/kW·h | ≤0.3 g/kW·h |
| Torque Reserve | 15–30% | 15–30% |
| Idle Speed | 700 rpm | 700 rpm |
| Emission Standard | IMO Tier II | IMO Tier II |
| Dry Weight | 1450 kg | 2050 kg |
Actual specifications may vary by engine model, emission configuration and market. Always confirm the complete engine model and technical documentation before installation or replacement planning.
What Models Are Available in the Weichai M21 Series?
The MGO model range includes several commercial power ratings.
6M21 Models
- 6M21Y815-23E200 — 599 kW / 815 PS at 2300 rpm
- 6M21Y900-23E200 — 662 kW / 900 PS at 2300 rpm
- 6M21Y1000-23E200 — 735 kW / 1000 PS at 2300 rpm
8M21 Models
- 8M21Y1000-23E200 — 735 kW / 1000 PS at 2300 rpm
- 8M21Y1100-23E200 — 809 kW / 1100 PS at 2300 rpm
- 8M21Y1250-23E200 — 919 kW / 1250 PS at 2300 rpm
- 8M21Y1360-23E200 — 1000 kW / 1360 PS at 2300 rpm
The appropriate power rating should be selected according to the vessel’s propulsion requirements, operating profile and matching requirements for the transmission and propeller system.
What Are the Main Advantages of the Weichai M21?
High Power Output in a Compact Package
The M21 series combines turbocharging and intercooling with a compact engine design to deliver high power for marine propulsion applications.
The 6M21 produces up to 735 kW from 12.54 L of displacement, while the 8M21 extends the available output to 1000 kW. This combination of displacement and power output provides flexibility when vessel builders and operators consider engine room layout and propulsion requirements.
High-Pressure Common Rail Fuel Injection
The M21 uses a 2200 bar high-pressure common rail fuel system controlled by the ECU.
Precise electronic fuel control supports accurate fuel delivery under different operating conditions. The common rail system also supports responsive engine operation, efficient combustion and stable fuel system performance.
Low-Speed Torque and Load Response
Marine vessels can operate under changing loads during maneuvering, acceleration and route operation.
The M21 series is designed to provide strong low-speed torque and responsive load performance. Its listed 15–30% torque reserve provides additional operating flexibility when engine load changes.
Fuel and Oil Consumption
The minimum specific fuel consumption is 204 g/kW·h, while oil consumption is listed at no more than 0.3 g/kW·h.
These figures provide useful reference points when evaluating engine operating efficiency. Actual fuel consumption depends on vessel load, hull condition, propeller matching and operating conditions.
Intelligent Diagnostic Support
The M21 uses a proprietary ECU and can support intelligent diagnostic and monitoring functions.
Remote diagnostic capability, maintenance guidance and service reminders can help operators monitor engine conditions and plan maintenance activities. The electronic system also supports sensor integration for intelligent vessel applications.
What Vessels Can Use the Weichai M21?
The M21 power range makes it suitable for a variety of marine propulsion applications.
Cargo and Transport Vessels
The 6M21 and 8M21 provide propulsion options for vessels requiring approximately 599–1000 kW.
The available cylinder configurations and power ratings provide flexibility when selecting an engine according to vessel size, load requirements and propulsion system design.
Fishing Vessels
Fishing vessels may require dependable propulsion performance during long operating hours and changing load conditions.
The M21 series combines high power output with electronically controlled common rail fuel injection, making it suitable for marine applications where propulsion performance and fuel management are important.
Passenger and Public Service Vessels
Higher-output M21 configurations can also be used for passenger and public service applications, depending on vessel design and propulsion requirements.
Engine selection should consider not only rated power, but also engine weight, installation dimensions, transmission matching and the vessel’s intended operating profile.
Weichai M21 Series Marine Diesel Engine Maintenance Schedule
The following maintenance intervals are general marine diesel service recommendations for the Weichai M21 series. Actual intervals should be adjusted according to operating conditions and the maintenance manual for the specific engine model.
| Service Item | Standard Operating Conditions | Severe Operating Conditions |
|---|---|---|
| Engine oil and filter | Every 250–500 operating hours | Every 250 operating hours |
| Fuel filter element | Every 250–500 operating hours | Every 250 operating hours |
| Fuel-water separator | Drain daily; inspect during routine service | Drain daily; inspect more frequently |
| Raw-water pump impeller | Inspect every 500 hours or annually | Inspect every 250 hours |
| Air filter | Inspect at every routine service; replace according to restriction indicator | Inspect monthly; replace when necessary |
| Coolant condition | Check every 6 months | Check every 3 months |
| Heat exchanger | Inspect and clean annually | Inspect and clean every 6 months |
| Valve clearance | Check according to the manufacturer’s service manual | Shorten inspection intervals according to operating conditions |
| Cooling system hoses and connections | Inspect every 500 operating hours | Inspect every 250 operating hours |
| Turbocharger and intake system | Inspect every 500 operating hours | Inspect every 250 operating hours |
Maintenance Note: Marine engines often operate continuously for extended periods, making engine-hour tracking essential. Shorten service intervals when using contaminated fuel, operating under sustained high loads, or working in harsh marine environments. Always follow the official Weichai maintenance manual for the specific M21 engine model and serial number.
What Are the Common Wear Parts for the Weichai M21?
Like other high-power marine diesel engines, the M21 requires regular inspection and replacement of service components that are subject to normal wear or contamination during operation.
The specific replacement parts required depend on the engine model, operating hours, fuel quality and maintenance conditions.
Fuel Filters and Water Separation Components
The M21’s 2,200 bar common rail system requires clean fuel to maintain stable injection performance. Fuel filters and water separators help prevent dirt, particles, and moisture from entering the fuel supply system.
Proper filtration helps reduce premature wear on precision components, including the high-pressure fuel pump and injectors. When replacing filter elements, check the engine model and configuration to ensure correct compatibility.
Oil Filters and Sealing Components
Oil filters are routine service items that help maintain lubricant cleanliness. Filter seals, O-rings and other sealing components may also need replacement during regular maintenance or when servicing related systems.
Correct filter and seal selection should be based on the engine model and original part reference.
Air Filter Elements
Air filter elements can gradually become restricted by dust and airborne contaminants. In marine environments, the operating environment and vessel application can affect inspection and replacement requirements.
A clean air intake system supports stable airflow and efficient engine operation.
Cooling System Service Parts
Cooling system maintenance may involve replacement of components such as hoses, seals and gaskets when wear, leakage or deterioration is identified.
The specific cooling system configuration can vary depending on the vessel installation, so replacement parts should be verified against the engine and vessel specifications.
Fuel Injection System Components
High-pressure fuel system components are precision parts and should not be replaced based only on the general M21 engine family name.
When replacing fuel injectors, common rail components, valves or other fuel system parts, verify the complete engine model, original part number and component reference before ordering.
What Should Be Checked Before Ordering Weichai M21 Replacement Parts?
The M21 series includes different configurations and commercial power ratings. A part should not be selected based only on the general engine family name.
Before ordering replacement components, verify:
- Complete engine model
- Engine serial number
- Original part number, where available
- Power rating and application
- Fuel system or engine configuration
This information helps reduce the risk of ordering a component that is not compatible with the specific marine engine.
For common rail fuel system parts and other precision components, matching the correct part number is especially important.
More Weichai Engine Guides
- Weichai M33 Marine Diesel Engine for Fishing Boats and Inland Waterway Vessels
- Weichai M55 Marine Diesel Engine for Heavy-Duty Commercial Vessels and Marine Propulsion
- Weichai CW250 Marine Diesel Engine for Large Fishing Vessels and Cargo Ships
- Weichai 16WH17 Marine Diesel Engine for Large-Scale Shipboard Power Generation
Read more:
- Weichai WP5N Engine Specs and Applications for Refrigerated Trucks
- Weichai WP7H Engine Specs and Applications for 130-220 PS Tractors
- Weichai M45 Marine Diesel Engine for Luxury Yachts and Large Passenger Ships
- Weichai 8WH17 Marine Diesel Engine for Coastal Cargo Ships and Fishing Vessels
FAQ About The Weichai M21 Marine Diesel Engine
What is the difference between the 6M21 and 8M21?
The main difference is the engine configuration and displacement. The 6M21 is an inline-six with a displacement of 12.54 L and covers 599–735 kW in the listed MGO models. The 8M21 is a V8 with a displacement of 16.72 L and covers 735–1000 kW.
What fuel system does the Weichai M21 use?
The M21 series uses a 2200 bar high-pressure common rail fuel system with electronic ECU control.
What fuel does the M21 series use?
The MGO models in the current product range use MGO (marine gas oil). Operators should confirm the approved fuel specification for their exact engine model before operation.
What is the maximum power of the M21 series?
The MGO model range reaches 1000 kW / 1360 PS at 2300 rpm with the 8M21Y1360-23E200.
What emission standards does the M21 meet?
The listed MGO models are rated for IMO Tier II. Emission requirements and configurations can vary by engine model and market, so the specifications for the exact engine should be confirmed before installation or operation.
How much fuel does the M21 consume?
The minimum specific fuel consumption is listed as 204 g/kW·h. Actual fuel consumption varies with vessel loading, operating conditions, propulsion system matching and other factors.
How can I identify the correct M21 replacement part?
Provide the complete engine model, serial number and original part number whenever possible. The M21 family includes multiple configurations, so these details should be checked before ordering fuel system parts or other replacement components.
Summary
The Weichai M21 series is a high-power marine diesel engine family covering 599–1000 kW at 2300 rpm. Available as the 6M21 inline-six and 8M21 V8, the series combines turbocharging and intercooling with a 2200 bar high-pressure common rail fuel system and electronic engine control.
Key specifications include 12.54–16.72 L displacement, minimum specific fuel consumption of 204 g/kW·h and a torque reserve of 15–30%.
For vessel operators, shipyards and marine engine service providers, selecting the appropriate M21 configuration requires consideration of the vessel’s power requirements, propulsion system and operating profile. Regular attention to filters, sealing components and other service parts can support reliable engine operation.
When sourcing replacement parts, always verify the complete engine model, serial number and original part number before ordering.
Brand names and vehicle or equipment references are used for identification and compatibility purposes only. Replacement components are aftermarket unless explicitly stated otherwise.