Mercedes SLK R172 Engines — The Complete UK Guide
Every engine fitted to the R172 roadster — from the M271 1.8-litre turbo fours to the M274 2.0-litre replacements, the OM651 diesel, the M276 V6 in the SLK 350 and AMG SLC 43, and the naturally aspirated M152 V8 in the SLK 55 AMG. Real UK replacement costs, honest failure data, and the engine changes that came with the 2015 SLC facelift. Backed by real UK R172 enquiries in 2025 [MB-VERIFIED].
Explore R172 Engines
Mercedes SLK R172 Engine Codes — The Complete Database
Every engine fitted to the R172 roadster specifically — spanning both pre-facelift SLK (2011–2015) and facelift SLC (2015–2020) variants.
Overview
Mercedes SLK R172 — Overview
The R172 is the third-generation SLK-Class, launched in January 2011 at the Geneva Motor Show as the successor to the R171.
Built in Bremen, Germany, it features a retractable hardtop, a 2,484 mm wheelbase, and a front-engine, rear-wheel-drive layout. The engine range spans the M271 1.8-litre turbo four-cylinder (2011–2015), the M274 2.0-litre turbo four-cylinder (2015–2020 facelift), the OM651 2.1-litre diesel four-cylinder (2012–2020), the M276 3.5-litre V6 (SLK 350) and 3.0-litre twin-turbo V6 (AMG SLC 43), and the M152 5.5-litre naturally aspirated V8 in the SLK 55 AMG. A 2015 facelift brought new engines, the 9G-Tronic automatic transmission, and the SLC name. The R172 was the first SLK to offer a diesel engine and the last to feature a naturally aspirated V8.
Key Facts
Platform
Mercedes R172 (shared with W204 C-Class)
Predecessor
R171
Successor
— (discontinued after 2020)
Sibling platform
W204 C-Class
Market Intelligence
The R172 SLK/SLC generated real UK engine enquiries in 2025 [MB-VERIFIED], concentrated on the M271/M274 four-cylinders and OM651 diesel as these cars enter enthusiast-owner territory.
Best & Worst Engines
Best Petrol Overall
M276.955 (SLK 350, 3.5-litre V6)
“The 3.5-litre M276 V6 delivers 306 PS of naturally aspirated power — smooth, responsive, and with a sound that no turbocharged four can match. It's the R172's sweet spot: V6 refinement without the M152's running costs, and more reliable than the M271 four-cylinder. The M276 is a well-regarded engine with good reliability, though timing chain issues affect some examples.”
Who it's for: buyers who want V6 smoothness and the classic roadster experience without AMG bills.
Highest Risk
M271.860/M271.861 (SLK 200 / SLK 250, 2011–2015)
“The 1.8-litre M271 turbo four is a great engine — but it comes with known issues: timing chain stretch, camshaft adjuster wear, and oil leaks from the camshaft solenoid. The M274 that replaced it in the 2015 facelift is a much safer bet. If you're buying a pre-facelift SLK 200 or SLK 250, budget for timing-chain inspection.”
Who it's for: buyers willing to accept higher maintenance costs for the pre-facelift experience.
Most Expensive Failure
M152.980 (SLK 55 AMG, 5.5-litre V8)
“The 5.5-litre M152 V8 is a masterpiece — 422 PS of naturally aspirated AMG thunder, exclusive to the SLK 55 AMG. It features cylinder deactivation derived from Formula 1 technology and weighs just 187 kg. But when it fails, it fails expensively. V8-specific parts, AMG labour rates, and the sheer complexity of this engine mean replacement bills frequently hit five figures. It's the last naturally aspirated V8 SLK — treat it as the special car it is.”
Who it's for: collectors and enthusiasts with deep pockets who want the last naturally aspirated V8 SLK.
Best Value
M274.920 (SLC 200 / SLC 300, 2015–2020)
“The 2.0-litre M274 turbo four is a significant improvement over the M271 — 184 PS in the SLC 200 and 245 PS in the SLC 300, with 300 Nm and 370 Nm of torque respectively. It's more reliable, more responsive, and more efficient than the engine it replaced. The SLC 300 is the sweet spot — 245 PS in a lightweight roadster is more than enough for UK roads.”
Who it's for: buyers who want the best combination of performance, reliability, and value in the R172 range.
Most Overlooked
M276.823 (AMG SLC 43, 3.0-litre twin-turbo V6)
“The 3.0-litre twin-turbo V6 in the AMG SLC 43 produces 367–390 PS — more than the SLK 55 AMG's 422 PS? No, but close, and with significantly better fuel economy. It replaced the M152 V8 in the facelift range and offers AMG performance without the V8's running costs. Often overlooked in favour of the V8, the SLC 43 is the smarter daily-driver choice.”
Who it's for: buyers who want AMG performance with V6 running costs.
Mercedes SLK R172 — Ownership Economics
The R172 rule
A £3,000–£4,500 OM651 recon against a £8,000 R172 sits at 38–56% of the car's value — safe. Even the M271 at £2,500–£4,500 against a £7,000 SLK 200 is 36–64% — within our 70% Mercedes threshold but approaching it on lower-value examples. The R172 is a premium roadster with strong enthusiast values; engine replacement is generally viable. The only exceptions are the AMG models — but if you can afford a £15,000+ SLK 55 AMG or SLC 43, you can afford the maintenance. For the M152 V8, the maths is different — it's the last naturally aspirated V8 SLK, a collector's item with collector's bills.
Common Problems
R172 Engine Replacement Costs — By Engine and Condition
No Generation variance from the Model Page's baseline figures — R172 roadster shares its W204-derived engine bay with the C-Class, so costs are inherited directly per the Authority Model, with no divergence note required. AMG costs reflect AMG-specific parts and specialist labour requirements.
Core Variants
Core Variants
Diesel Variants
Scope note: All variants listed are R172 roadster only. Pre-facelift models (2011–2015) are badged SLK; facelift models (2015–2020) are badged SLC. The R172 was the last SLK/SLC generation — discontinued after the 2020 model year.
Market Intelligence
Most Requested E90 Engines (2025)
- 1.1. M271.860/861 (SLK 200/250) — pre-facelift volume [PATTERN DATA]
- 2.2. M274.920 (SLC 200/300) — facelift volume [PATTERN DATA]
- 3.3. OM651.980 (250 CDI/250 d) — diesel choice [PATTERN DATA]
Most Requested E90 Variants
- 1.1. SLK 200
- 2.2. SLK 250 CDI
- 3.3. SLC 300 [PATTERN DATA]
Average E90 Replacement Cost
£2,500–£6,500 reconditioned, supply only [MB-QUOTE]
Most Common E90 Failures
- 1.1. M271 timing chain/camshaft adjusters
- 2.2. Vario-roof mechanism failure
- 3.3. OM651 injector seal failure [PATTERN DATA]
Mercedes SLK 200 R172 (M271)
5
enquiries
Mercedes SLK 250 CDI R172 (OM651)
3
enquiries
Mercedes SLC 300 R172 (M274)
2
enquiries
FAQ
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