Mercedes-Benz OM603 3.0L Inline-6 Diesel Engine

Description

For sale is a used Mercedes-Benz OM603 3.0L inline-6 diesel engine, a respected powerplant used in several classic Mercedes diesel models. This engine was removed from a donor vehicle and inspected prior to listing. It remains in good used condition, showing only normal wear consistent with age and proper maintenance. The engine is supplied as a long block and is suitable for direct replacement, restoration projects, or rebuild preparation.
The OM603 engine is known for its smooth operation, strong torque delivery, and excellent long-distance reliability. It was designed to provide refined diesel performance while maintaining Mercedes-Benz’s reputation for durability. This unit is ideal for owners seeking to restore factory driving characteristics or keep their classic diesel Mercedes running dependably.

Performance & Reliability

The OM603 features a single overhead camshaft, 12-valve cylinder head, cast-iron block, and mechanical diesel injection system, engineered for efficiency and long service life. Prior to removal, the engine operated normally with no abnormal knocking or excessive smoke. During inspection, the following checks were completed:
Engine rotates freely
Compression remains even across cylinders
No visible cracks in block or cylinder head
Oil passages and mounting points intact
The OM603 is capable of very high mileage when properly serviced. Its mechanical injection system makes it easier to maintain compared to later electronic diesel engines. When installed in its original application, it integrates directly with factory cooling, exhaust, and drivetrain systems.
This engine is suitable for stock restorations, daily driver replacements, and classic Mercedes diesel rebuild projects. It also provides a strong base for preventative maintenance or light overhaul work.

Fitment

Fits in:
Mercedes-Benz W124 300D
Mercedes-Benz W126 300SD / 300SDL
Mercedes-Benz W140 300SD
Other models originally equipped with the OM603 engine
This is a direct-fit engine for the above applications when installed with correct accessories and wiring. No modification is required when replacing an original OM603 engine. Buyers should confirm engine code and vehicle compatibility before purchase.

Warranty & Installation

This engine includes a 6-month limited mechanical warranty, covering internal engine components under normal operating conditions. External accessories, injectors, pumps, and wear items such as belts, hoses, and gaskets are not covered due to prior use.
Professional installation is strongly recommended. During installation, it is advised to:
Replace engine oil, coolant, and filters
Inspect timing components and seals
Check fuel system connections
Perform an initial test run before regular operation
Proper installation and service help ensure reliable performance and extended engine life.

If you are searching for a genuine Mercedes-Benz OM603 3.0L inline-6 diesel engine, this used unit offers dependable performance, correct fitment, and excellent value for classic Mercedes diesel ownership. It is an ideal replacement for a worn or damaged engine while preserving factory specifications and reliability. With proven engineering and solid condition, this engine is ready to return your vehicle to smooth and economical service.