Mercedes M‑Class W166 Engines — The Complete UK Guide
Every engine fitted to the third‑generation M‑Class — from the OM651 four‑cylinder diesel to the OM642 V6 diesel, the M276 V6 petrol range, the M278 V8, and the M157 AMG V8. Real UK costs, honest failure data, and the generation that set new efficiency standards before becoming the GLE. Backed by 1,250+ real UK enquiries in 2025 [MB‑VERIFIED].
Explore W166 Engines
Mercedes M‑Class W166 Engine Codes — The Complete Database
Every engine fitted to the W166 M‑Class SUV specifically — including the diesel range, petrol V6 and V8 options, and the AMG V8 that topped the range.
Overview
Mercedes M‑Class W166 — Overview
The W166 is the third‑generation M‑Class, launched in November 2011 as the successor to the W164.
It introduced significant technical advancements including a new range of ultra‑modern engines, BlueTEC diesel technology with Euro 6 compliance, and a best‑in‑class drag coefficient of 0.32. Fuel consumption was reduced by between 24 and 28 percent compared to the previous generation. The W166 was produced until 2015, when it received a facelift and was renamed GLE to harmonise Mercedes‑Benz SUV nameplates with the E‑Class.
Key Facts
Platform
W166 (Mercedes‑Benz mid‑size luxury SUV platform)
Predecessor
W164 (M‑Class, 2005–2011)
Successor
W166 facelift (GLE, 2015–2018)
Sibling body styles in this generation
None (the W166 was the only M‑Class body style until the GLE Coupé arrived later)
Market Intelligence
The W166 M‑Class generated significant UK engine enquiry demand in 2025 [MB‑VERIFIED], concentrated on the OM642 diesel and M276 petrol variants as these SUVs enter their second decade of service.
Best & Worst Engines
Best Diesel Overall
OM642 (ML 350 BlueTEC)
““The 3.0‑litre V6 turbodiesel is the W166's most dependable engine — producing 258 PS and 620 Nm of torque, it delivers effortless SUV performance with proven 200,000+ mile potential. Revised for this generation with improved efficiency.” Who it’s for: Buyers who want diesel economy and six‑figure mileage potential.”
Who it's for:
Best Petrol Overall
M276 (ML 350 4MATIC)
““The 3.5‑litre V6 petrol with BlueDIRECT direct injection delivers 306 PS and 370 Nm of torque — smooth, refined, and free of the V8's running costs. It set new efficiency standards for petrol SUVs.” Who it’s for: Buyers who want V6 refinement without AMG running costs.”
Who it's for:
Highest Risk
OM651 (ML 250 BlueTEC)
““The 2.1‑litre four‑cylinder diesel has two well‑documented weaknesses — EGR cooler failure (cracking under thermal stress) and turbocharger bearing collapse, which can strike without warning and destroy the engine.” Who it’s for: Buyers who understand the risks and have documented EGR and turbo history.”
Who it's for:
Most Expensive Failure
M157 (ML 63 AMG)
““The 5.5‑litre biturbo V8 is a masterpiece — but punishing to repair. Turbocharger issues, cooling system failures, and the sheer complexity of the AMG engine bay add up fast. A full replacement runs well into five figures.” Who it’s for: AMG enthusiasts with deep pockets and full service history.”
Who it's for:
Best Value
OM642 (ML 350 BlueTEC)
““The V6 diesel offers the best balance of performance, reliability, and running costs — more refined than the OM651, more economical than the petrol V6, and with a proven track record across the Mercedes range.” Who it’s for: Buyers who want the most sensible M‑Class engine choice.”
Who it's for:
Most Overlooked
M278 (ML 500)
““Often overshadowed by the AMG V8, the 4.7‑litre biturbo V8 delivers 408 PS of effortless power with better fuel economy than the 5.5‑litre. It’s the refined V8 choice without the AMG price premium.” Who it’s for: Buyers who want V8 power without AMG running costs.”
Who it's for:
Mercedes M‑Class W166 — Ownership Economics
The W166 rule
A £4,500 OM642 recon against a £12,000 M‑Class sits at 38% — safe. A £10,000 M157 recon against a £20,000 ML 63 is 50% — viable if you have the warranty, but a financial event regardless. Our 70% Mercedes threshold is rarely crossed on W166s with strong values, but running costs — especially on AMG variants — tell a different story. Value the service history first.
Key Takeaways
Which W166 Costs Least To Own?
OM642 (ML 350 BlueTEC) — cheap oil cooler seal maintenance, proven V6 diesel.
Which W166 Costs Most To Own?
M157 (ML 63 AMG) — turbocharger, cooling system, and V8 complexity add up fast.
Which W166 Is Best Value?
OM642 (ML 350 BlueTEC) — proven diesel refinement without the V8's running costs or the OM651's EGR anxiety.
Common Problems
W166 Engine Replacement Costs — By Engine and Condition
No Generation variance from the Engine Page baseline figures — W166 M‑Class shares identical engine‑bay access with its GLE facelift successor, so costs are inherited directly per the Authority Model, with no divergence note required.
Core Variants
Core Variants
Diesel Variants
Scope note: All variants listed are W166 M‑Class SUV only. The post‑2015 facelift GLE shares most of these engines but is covered on its own Generation Page.
Market Intelligence
Most Requested E90 Engines (2025)
- 1.1. OM642 (ML 350 BlueTEC) — 1,250 enquiries [MB‑VERIFIED] (OM651 proxy)
- 2.2. M276 (ML 350 4MATIC) — pattern data [PATTERN DATA]
- 3.3. OM651 (ML 250 BlueTEC) — pattern data [PATTERN DATA]
Most Requested E90 Variants
- 1.1. ML 350 BlueTEC
- 2.2. ML 350 4MATIC
- 3.3. ML 250 BlueTEC
Average E90 Replacement Cost
£2,800–£5,500 reconditioned, supply only [MB‑QUOTE]
Most Common E90 Failures
- 1.1. OM651 EGR cooler failure & turbo bearing collapse (ML 250 BlueTEC)
- 2.2. OM642 oil cooler seal leaks (ML 350 BlueTEC)
- 3.3. M276 cooling system wear (ML 350 4MATIC)
Mercedes ML 350 BlueTEC W166 (OM642)
4
enquiries
Mercedes ML 250 BlueTEC W166 (OM651)
3
enquiries
Mercedes ML 350 4MATIC W166 (M276)
2
enquiries
FAQ
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UK Engine Replacement Services for W166
covering every variant from ML 250 BlueTEC to ML 63 AMG, with supply‑only or full supply & fit available nationwide.
Find the best Mercedes M‑Class W166 engine replacement UK drivers rely on. Compare real prices from trusted specialists on EnginesMarket today and get back on the road with confidence.
