The Mercedes-Benz OM603.971 is a 2,996 cc, inline-six, naturally aspirated diesel engine produced between 1995 and 1998. It features indirect injection via a pre-chamber design and a robust SOHC valvetrain with mechanical tappets. Designed for durability in executive and light commercial applications, it delivers 60 kW (82 PS) at 4,200 rpm and 190 Nm of torque at 2,200 rpm, offering smooth low-end pull suitable for relaxed cruising and fleet use.
Fitted to the W124 300D and T2 610D platforms, the OM603.971 was engineered for longevity and ease of maintenance under sustained highway operation. Emissions compliance was achieved through mechanical fuel control and an oxidation catalyst, meeting Euro 1 standards. Its simple architecture prioritised reliability and predictable service costs over performance, appealing to commercial operators and conservative drivers.
One documented service concern is cylinder head cracking between exhaust valve seats, particularly under sustained load or cooling system neglect. This issue, referenced in Daimler Service Bulletin 07-03-97, is attributed to thermal stress in the cast-iron head. From 1996, revised cylinder head casting procedures and improved cooling system maintenance protocols were introduced to mitigate the risk.
Production years 1995–1998 meet Euro 1 standards (VCA UK Type Approval #VCA/EMS/5680). No Euro 2 compliance for this variant.
The Mercedes-Benz OM603.971 is a 2,996 cc inline-six diesel engine designed for executive and light commercial vehicle applications (1995–1998). It utilises indirect injection and a mechanically actuated fuel system to deliver smooth power delivery and straightforward serviceability. Designed to meet Euro 1 emissions standards, it balances durability with acceptable fuel economy for its era.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,996 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 92.0 mm × 90.0 mm | |
| Power output | 60 kW (82 PS) @ 4,200 rpm | |
| Torque | 190 Nm @ 2,200 rpm | |
| Fuel system | Bosch M mechanical inline injection pump | |
| Emissions standard | Euro 1 | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Chain-driven camshaft | |
| Oil type | SAE 10W-40, ACEA B2/B3 | |
| Dry weight | 228 kg |
The naturally aspirated design provides smooth, linear power delivery ideal for highway cruising and light-duty use, but requires attentive cooling system maintenance to prevent cylinder head cracking under thermal stress. SAE 10W-40 oil meeting ACEA B2/B3 specifications is essential for lubricating the mechanical injection pump and valvetrain. Overheating must be avoided, as the cast-iron cylinder head is prone to inter-valve cracking, especially in high-mileage units. The Bosch M injection pump requires specialist calibration for servicing and is sensitive to fuel contamination. Adherence to 15,000 km oil change intervals and regular coolant replacement is critical for long-term reliability.
Oil Specs: Requires SAE 10W-40, ACEA B2/B3 specification (Mercedes Service Bulletin 07-03-97). Compatible with MB 229.1.
Emissions: Euro 1 certification applies to all production years (1995–1998) (VCA Type Approval #VCA/EMS/5680). No Euro 2 compliance for this variant.
Power Ratings: Measured under DIN 70020 standards. Output is consistent across all markets for this engine code.
Mercedes-Benz Technical Information System (TIS): Docs A35714, A36090, A35803, SB 07-03-97
VCA Type Approval Database (VCA/EMS/5680)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz OM603.971 was used across Mercedes-Benz's W124 and T2 platforms with longitudinal mounting. This engine received platform-specific adaptations-reinforced engine mounts in the T2 for payload stability and revised exhaust manifolds for underfloor clearance-and from 1996, updated cylinder head casting procedures were implemented to address thermal stress concerns, creating minor service part differences. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front face of the engine block, near the timing cover (Mercedes TIS A35803). The 8th digit of the VIN identifies the engine type ('3' for OM603 series). Pre-1996 engines have a smooth exhaust manifold casting; post-1996 units may show revised ribbing for strength. Critical differentiation from turbocharged OM603 variants: OM603.971 has no turbocharger and uses a Bosch M mechanical injection pump with a distinctive inline plunger design. Service parts require model year verification—cylinder heads before 07/1996 are not interchangeable with later revised castings (Mercedes SB 07-03-97).
The OM603.971's primary reliability risk is cylinder head cracking between exhaust valves, with elevated incidence in vehicles subjected to frequent high-load operation or cooling neglect. Daimler internal reports from 1997 indicated a measurable rate of head failures in pre-1996 units, while UK DVSA data shows older diesel models are disproportionately represented in coolant system-related MOT failures. Inadequate coolant changes and prolonged idling increase thermal cycling stress, making proactive cooling system maintenance critical.
Analysis derived from Mercedes-Benz technical bulletins (1995-1998) and UK DVSA failure statistics (1995-2005). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM603971.
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