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Mercedes-Benz OM651

OM651 Engine

The OM651 is a diesel engine manufactured by Mercedes-Benz. It has a displacement of 2.1 liters and was produced from 2008 to 2020.

Typical Use Cases

  • Mercedes C-Class (W204/W205): 2008–2018
  • Mercedes E-Class (W212): 2009–2016
  • Mercedes GLC (X253): 2015–2018
  • Mercedes GLA/CLA (X156/C117): 2013–2019
  • Mercedes Sprinter: 2009–2018
  • Infiniti Q30/Q50: 2015–2019

This overview summarizes the reliability of the Mercedes-Benz OM651, including common issues and cost drivers.

Mercedes-Benz OM651 engine
Image credit: Wikimedia Commons · CC0

Technical Specifications

Manufacturer
Mercedes-Benz
Fuel Type
Diesel
Displacement
2.1 L
Production
2008–2020
Power Output
136 hp
Emissions
Euro 5, Euro 6

Reliability Analysis

The engine's reliability can be assessed as moderate at best, given the provided metrics. The risk score of 6.5 (on a 10-point scale, where higher values indicate greater potential for operational disruptions) suggests a noticeable likelihood of performance inconsistencies or failures in real-world use, such as unexpected downtime or reduced efficiency under load. This is compounded by two known issues, both classified as high severity, which point to significant vulnerabilities that could impact core functionality without mitigation. Overall, these factors indicate that the engine requires careful monitoring and potential updates to achieve dependable performance.

Conditionally Recommended

Autoscore Verdict

Conditionally recommended. The risk score of 6.5 indicates moderate risks that should be addressed through additional safeguards before full implementation.

Risk Score
6.5
out of 10

Common Problems & Weak Points

IssueTypical MileageRepair Cost (Est.)Severity
Piezo Injector Failure~100,000 km€1500 – €2500High
Timing Chain Stretch~250,000 km€2000 – €3500High

Piezo Injector Failure

If you're looking at a used car from the early models, specifically 2008 to 2011, there's a known issue with the piezo injectors, which are components that deliver fuel into the engine. These were made by Delphi and have been found to be defective in those years, leading to failure. The risk is high for these early models, and it's a serious problem that can affect engine performance. It typically happens around 100,000 kilometers. Fixing it usually costs between 1,500 and 2,500 euros. Newer models use a more reliable solenoid replacement, so they're less likely to have this issue.

Typical Mileage: 100,000 km
Cost: €1500–2500

Timing Chain Stretch

This car has a potential issue with the timing chain, which is a key part of the engine that keeps everything running in sync. In this model, it's a single-row chain that can stretch as the car racks up high mileage—typically around 250,000 km. This has a medium likelihood of happening, but it's a high-severity problem because it can lead to serious engine damage if it fails.

Fixing it isn't straightforward: the chain is located at the back of the engine, so the entire engine usually has to be removed from the car to access it. Repairs generally cost between 2,000 and 3,500 euros, depending on labor and parts. If you're considering this used car, it's worth checking the mileage and service history to see if this could be a future concern.

Typical Mileage: 250,000 km
Cost: €2000–3500

Buyer's Inspection Checklist

  • For 2008-2011 models, confirm if defective Delphi piezo injectors have been replaced with reliable solenoid injectors to avoid failure.
  • At high mileage, inspect for timing chain stretch symptoms like rattling noises, as the single-row chain is at the back and requires engine removal for repair.

Frequently Asked Questions

Is the OM651 engine reliable?

The OM651 has known weak points, but with good maintenance the reliability is solid. See the risk analysis and common problems for specifics. Start a report for a specific car.

How expensive are typical repairs?

Common repairs fall into a mid-range cost band depending on the issue and workshop. Check the cost ranges in the table. Use the used car report for specific listings.

Which model years are best for this engine?

Newer production years often include technical updates. Review the production years and revisions in the specs. Use Car Check for quick screening.

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