Wärtsilä 25 - the power to target net-zero

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Wärtsilä 25 - the engine with true fuel flexibility

The Wärtsilä 25 is a medium-speed 4-stroke marine engine with a future-proof, upgradeable modular structure that makes it easier than ever for you to target net-zero. With the Wärtsilä 25 you can transition to greener future fuels simply by replacing selected engine components, which significantly shortens the overhaul time and reduces complexity.

Available in cylinder configurations from 6L to 9L and with a power output ranging from 1.9–3.4 MW, the Wärtsilä 25 provides reliable performance whether you are using it as a robust main propulsion engine or as a cost-efficient and flexible auxiliary engine. The engine is available in both diesel and dual-fuel versions.


Key benefits

  • High power output per cylinder, means fewer cylinders are needed, resulting in a more compact engine
  • Fewer overhauls through prolonged component lifetime - time between overhauls extended by a minimum of 30%
  • Outstanding fuel economy, low emissions, and smoke-free operation at all loads
  • Easily meets IMO Tier III requirements - the diesel engine complemented with an integrated Wärtsilä NOR® NOx reducer
  • Modular design for faster, easier upgrades and conversions to future fuels
  • Perfect for mechanical, diesel-electric and hybrid installations
  • 100% power output from both ends
  • Optimised to run both at both constant and variable speeds

Wärtsilä 25 product video

Expert Interview - Wärtsilä 25

One engine, two versions

The Wärtsilä 25 is perfect for use as a main engine onboard smaller merchant vessels, fishing boats, tugs, dredgers, and offshore support vessels. Whether you are looking for a diesel, biofuel, or dual-fuel engine for your main or auxiliary application, the Wärtsilä 25 is the answer.

Both engine versions feature common rail, high-pressure fuel injection that enables cylinder-wise combustion control and fuel-injection settings for each operating point. The diesel version features single-stage turbocharging and the dual-fuel version with two-stage  turbocharging that offers the highest overall performance. This means more power with fewer cylinders and better environmental performance – with the same service heights.  

A future-proof investment

No matter what version of the engine you start with, the upgrade path is secured by the Wärtsilä 25’s outstanding modularity, which future-proofs your investment.

The modular, upgradable design allows you to reduce vessel fuel consumption and emissions from the first mile while providing the readiness to run on alternative fuels whenever viable – all without compromising performance. Whatever future fuel emerges as the most appropriate for your operations, the Wärtsilä 25 is ready for the challenge.

Wärtsilä 25 and Wärtsilä 25DF Product guide and 3D models and drawings

Get technical data and system proposals for designing W25 and W25DF marine engine installations.

  • The Wärtsilä 25 lounge

    Experience the new Wärtsilä 25 engine - maximised flexibility, minimised emissions

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