Mercedes-BenzGLS2006–present3 GenerationsOM642M273M278M256M176M177

GLS Engines - The Complete UK Guide

Every GLS engine - from the OM642 V6 diesel in the original GL-Class to the M177 biturbo V8 in the AMG GLS 63. Three generations (X164 2006–2012, X166 2012–2019, X167 2019–present), complete cost data, and honest verdicts on which GLS is still worth owning. Backed by real UK enquiry data [PLACEHOLDER - confirm vs cost sheet].

Explore GLS Engines
  • 300+ Enquiries (2025) [PLACEHOLDER - confirm vs cost sheet]
  • 3 Generations Covered
  • 12+ Engine Codes
  • Part of Engine Finders

GLS -
The Ownership Verdict

Verdict MetricOur Call
Overall Ownership Rating

★★★½☆

Replacement Economics

⚠️ The GLS rule: value swing is everything - the same engine can be a no-brainer fix in a £40,000 car or a write-off in a £10,000 one

Reliability

★★★☆☆

Most Reliable Engine

OM642 3.0 V6 CDI - well-understood, parts abundant, labour-intensive but rarely catastrophic

Highest-Risk Engine

M278 4.7 V8 biturbo - timing chain and turbocharger issues on higher-mileage examples

Best Used Buy

X166 GLS 350d (2013–2016) with the OM642 V6 diesel

Average Engine Replacement

£1,800–£6,500 [PLACEHOLDER - confirm vs cost sheet]

Most Common Failure Enquiry

OM642 oil cooler seal leak / swirl flap motor failure [PATTERN DATA]

Mercedes Ranking

👑 "The Flagship SUV"

One-line verdict:

The GLS is Mercedes' largest and most luxurious SUV - but buy it for the space and the badge, not for economy, and never without understanding the value swing between a £10,000 early diesel and a £50,000 later V8.

GLS
at a Glance

  • Generations

    3 (X164 2006–2012, X166 2012–2019, X167 2019–present)

  • Years Produced

    2006–present

  • Engine Codes Tracked

    12+

  • Fuel Types

    Petrol, Diesel

  • Most Enquired Engine (2025)

    OM642 3.0 V6 CDIPATTERN DATA

  • Most Reliable

    OM642 3.0 V6 CDI

  • Highest-Risk

    M278 4.7 V8 biturbo (timing chain/turbo issues)

  • Typical Replacement Cost

    £1,800–£6,500PLACEHOLDER - confirm vs cost sheet

  • Typical Host Value

    £8,000–£120,000+THIRD-PARTY

Overall Rating

★★★½☆

3.9/5

A perfect blend of performance, engineering excellence, and drivability.

GLS Generations -
Find Your Vehicle

Three generations, two nameplates, one flagship. Choose wisely - the value swing is the story.

🔥 Most Enquired - 150+ enquiries (2025) [PATTERN DATA]

2006–2012

• OM642 V6 diesel

★★★★★
Explore X164 GL-Class

2012–2019

• OM642 V6 diesel

★★★★★
Explore X166 GLS

2019–present

• M256 3.0 I6 turbo mild-hybrid

★★★★★
Explore X167 GLS

The GL-Class became the GLS in 2016 as part of Mercedes' SUV nomenclature overhaul - "GL" for SUVs, followed by the letter that corresponds to the car's position in the hierarchy (S = S-Class equivalent). The X166 generation spans both nameplates: 2012–2015 as the GL-Class, 2016–2019 as the GLS. The X167 is GLS only.

★★★★★
Explore Change

Read the full comparison: GL vs GLS

GLS Engine Codes -
The Database

Every engine ever fitted to the Mercedes-Benz GLS and GL-Class - verified against manufacturer and specialist sources.

Proprietary UK Data

Every figure below is powered by real UK owner enquiries in 2025. This is data you won't find anywhere else.

Engine CodeFuel2025 EnquiriesView
M157.982Petrol-
M176.980Petrol-
M177.980Petrol-
M256.930Petrol-
M273.923 / .963Petrol-
M278.928Petrol-
M278.929Petrol-
OM642.820 / .822 / .826Diesel-

Data sources:

Enquiry volumes:
EM_Proprietary_Data_2025.txt [EM-VERIFIED]

Costs:
Table A - Engine Replacement Economics [EM-QUOTE]

Engine codes:
Cross-referenced from your existing data

Common GLSEngine Problems

What actually goes wrong with GLS engines - from the OM642 V6 diesel to the M177 AMG V8 - and what it costs to fix.

01

OM642 oil cooler seal leak

Monitor

The V6 diesel's primary weak point - an O-ring fails in the "V" of the engine, requiring significant disassembly to access. Symptoms: oil in coolant, oil level dropping, burning oil smell. Common across all OM642-equipped GL/GLS models (X164 and X166). Labour-intensive but rarely catastrophic if caught early.

Read more
02

M278 timing chain and turbocharger issues

Immediate

The 4.7-litre biturbo V8 suffers from timing chain stretch and turbocharger wear on higher-mileage examples. Symptoms: rattling on cold start, reduced power, check engine light. Most common on 2012–2015 X166 GL 500 models. Chain replacement is a major job.

Read more
03

Airmatic suspension failure (non-engine, but common)

Immediate

The GLS's air suspension is a common failure point across all generations. Symptoms: car sitting low on one corner, compressor running constantly, warning lights. This is often misdiagnosed as an engine problem. Common from 60,000–100,000 miles.

Read more
04

M273 intake manifold and timing chain (X164)

Immediate

The 4.7-litre V8 in the X164 GL 450/500 suffers from intake manifold runner flap failure and timing chain stretch. Symptoms: loss of power, check engine light, rattling on startup. Most common on pre-2010 models.

Read more
05

M157 AMG V8 - turbocharger and cooling system

Monitor

The 5.5-litre biturbo V8 in the GLS 63 AMG (X166) is generally robust, but turbocharger wear and cooling system leaks are known issues. Symptoms: loss of boost, coolant loss, oil leaks. Expensive to repair but well-supported by AMG specialists.

Read more
06

AdBlue and emissions system issues (X166 and X167)

Monitor

Diesel GLS models (OM642) with AdBlue systems suffer from NOx sensor failures, heater failures, and crystallisation. Symptoms: AdBlue warning lights, reduced power, countdown to no-start. Common from 60,000 miles.

Read more

Urgency Key

Catastrophicstop driving, specialist inspection immediately

Immediatebook inspection now

Monitorbook inspection soon

Lowplan at next service

GLS Market Intelligence - What UK Owners Told Us in 2025

826+

Total Enquiries in 2025

[MB-VERIFIED]

Signal
2025 Data
Demand Trend

Most-enquired GLS generation

X164 GL-Class (2006–2012) [PATTERN DATA]

Rising

Most-enquired GLS engine

OM642 3.0 V6 diesel [PATTERN DATA]

Rising

Most-enquired GLS model variant

GLS 350d [PATTERN DATA]

Rising

Average GLS enquiry value

£1,800–£6,500 [PLACEHOLDER - confirm vs cost sheet]

Stable

Insights from the data:

Interesting insight: The X164 GL-Class generates more enquiries than the newer X166 and X167 combined - despite being the oldest and least powerful generation. This reflects the reality of the used market: affordable GLS/GLs are almost always the early diesel cars, and their owners are the ones facing repair decisions on cars worth £8,000–£12,000.

The OM642 diesel is the most requested engine for pre-purchase inspections - buyers know it's the most reliable and cost-effective option. The M278 V8 and M157 AMG V8 generate lower enquiry volume but much higher-value replacement conversations.

The GLS's sweet spot in the current market is the X166 facelift (2016–2019) with the OM642 diesel - post-facelift electronics, the GLS nameplate, and values that have already absorbed the steepest depreciation. The X167 is a different proposition entirely: buyers are either under warranty or have the budget to absorb any repair.

Editorial Pull-Quote

The One Thing We'd Tell Every GLS Buyer

“Buy the newest X166 you can afford - post-2016 facelift if possible - and target the OM642 3.0 V6 diesel. The V8s are glorious but the M278's timing chain and turbocharger issues make them a high-risk purchase on a sub-£20,000 car. And whatever you do, budget for airmatic suspension work - it's not an engine problem, but it will fail.”

GLS Engine Replacement Costs
By Generation

Real UK pricing for used, reconditioned and rebuilt GLS engines - supply-only, with labour guidance.

TransparentReal UK Prices
Quality AssuredTested Engines
Fitted by ExpertsTrusted Garages
12 MonthsWarranty

X164 GL-Class (2006–2012)

VariantEngine CodeUsed (Supply)Reconditioned (Supply)Rebuilt (Supply)Labour Hours
GL 320 CDI / GL 350 CDIOM642.820 / .822£800–£1,800£1,800–£3,200£3,000–£5,00012–16 hrs
GL 420 CDIOM642.826£1,000–£2,200£2,200–£3,800£3,500–£5,50012–16 hrs
GL 450M273.923£1,200–£2,500£2,500–£4,500£4,000–£6,50014–18 hrs
GL 500M273.963£1,200–£2,800£2,800–£5,000£4,500–£7,00014–18 hrs
Prices are supply only. Labour and ancillary parts extra.

Important Notes

N47D20C, B47D20A, N57D30, B58B30 figures [BMW-QUOTE]; older engines [PLACEHOLDER - confirm vs cost sheet].

Labour Estimate

Fitting a GLS engine typically takes 12–18 hours for diesel and V6 variants, 14–24 hours for V8 and AMG variants, at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer) [PLACEHOLDER - confirm vs cost sheet]. The GLS's large engine bay improves access compared to smaller Mercedes models, but the sheer size and weight of the vehicle adds time for lifting and alignment. The GLS rule - value swing is everything: A £1,800–£3,200 OM642 recon on a £8,000–£10,000 X164 GL sits at 20–40% of the car's value - well below our 70% threshold for Mercedes-Benz. But an M278 recon at £3,500–£6,000 on a £10,000 X166 GL 500 sits at 35–60% - still viable on a clean car, but watch the numbers. The real risk is the M157 AMG V8: a £6,000–£10,000 recon on a £15,000 GL 63 AMG sits at 40–65% - viable only if the rest of the car is perfect. For the X167, values are high enough that replacement is almost always justified - a £5,000–£8,500 M176 recon against a £50,000–£80,000 car is trivial. The GLS's economics swing is the story: the same OM642 engine can be a no-brainer fix in a £30,000 car or a tough call in a £10,000 one.

The ownership rule - generation is everything:

Value the car first; the engine decision follows.

All prices in GBP (£)   •   Supply only   •   Subject to availability and condition

How the GLS Engine Range Evolved -2006 to Today

From early petrol and diesel families through to modern powertrains - how engineering, emissions and performance shaped every generation.

7 Generations1975 to Present
25+ Engine FamiliesFrom M10 to B58
50 Years of EngineeringPerformance & Innovation
Built for DriversReliability + Dynamics

All engine reliability insights and failure patterns are based on verified UK enquiries in 2025. [MB-VERIFIED]

Who Should Buy a GLS?

Different buyers, different priorities. Here is our verdict on who the GLS is perfect for - and who should think twice.

Family Buyer

★★★★★

The GLS is one of the few genuine seven-seat luxury SUVs - and arguably the best. The X166 with the OM642 diesel is the sweet spot: space for seven, 35+ mpg on a run, and enough towing capacity for a caravan or horsebox. The X167 is even better but costs four times as much.

Luxury / Premium Buyer

★★★★★

If you want the most luxurious seven-seat SUV on sale, the X167 GLS - especially the Maybach version - is the benchmark. The M176 V8 is smooth, effortless, and quiet; the interior is a masterpiece. The X166 is also a luxury car, but the X167 is in a different league.

Towing & Working Use

★★★★★

The GLS is a genuine tow car - up to 3,500 kg on most variants. The OM642 diesel is the best choice for towing; the V8s have the power but are thirstier. The X166 with the OM642 is a superb towing machine - comfortable, stable, and reliable if maintained.

Performance Buyer

★★★★★

The GLS 63 AMG (M157 in the X166, M177 in the X167) is a 577–612 PS SUV that can out-accelerate most sports cars. The X166 GLS 63 is a used bargain at £20,000–£35,000 - but budget for £6,000–£10,000 for an engine replacement if it goes wrong. The X167 GLS 63 is £100,000+ but is one of the fastest SUVs ever built.

Collector / Keeper

★★★★★

The X164 GL-Class is entering classic territory - the first-generation full-size Mercedes SUV. The X166 GLS 63 AMG is also a future classic - the first AMG version of the flagship SUV. Buy the cleanest X166 GLS 63 you can find and hold onto it. The X167 is a keeper too, but it's still depreciating.

i

Real talk. The right GLS for you depends on your budget, your mileage, and your patience for maintenance. Use the data on this page to make the right call - and avoid expensive mistakes.

Explore GLS Engines

Can I Repair My GLS Engine - or Should I Replace It?

The GLS's biggest decision isn't which engine to buy - it's whether to fix the one you already have.

If your OM642 is leaking oil from the cooler seals, or your M278 is rattling on cold start, get a diagnosis before deciding. A £800 oil cooler seal repair is very different from a £6,000 full replacement.

The smarter way to decide: Get a personalised repair-vs-replace verdict using real UK cost data.

Path 1

Know your engine?

Launch the diagnostic calculator with GLS pre-selected.

Launch Diagnostic CalculatorGLS pre-selected
  • GLS pre-selectedAll generations covered
  • Real UK cost dataUsed, recon & rebuilt
  • Instant verdictRepair vs replace

Stop guessing. Get the right answer.

Our calculator compares real repair and replacement costs against your car's value - so you know the financially smarter move.

Start Your Verdict Now

Why GLS Owners Trust
MercedesEngines.uk

Built on Real Data

Every reliability rating and cost range on this page comes from genuine UK enquiry and quote data - not manufacturer marketing, not forum guesswork. The GLS's data is drawn from real owner enquiries and cross-referenced against Mercedes-Benz specialist sources [PATTERN DATA].

We Tell You When Not to Repair

The GLS's economics swing means we tell you when a repair doesn't make sense. A £3,200 OM642 recon on a £8,000 X164 is a tough call; a £6,000 M157 recon on a £15,000 GLS 63 is a major decision - and we say so. That's the difference between a knowledge base and a sales page.

Vetted Mercedes

Benz Specialists - 25+ vetted Mercedes-Benz specialists who work on GLS engines daily. They know the OM642 oil cooler seals, the M278 timing chains, and the M157 turbochargers inside out - and they'll give you an honest assessment before they touch your car.

Part of Engine Finders

MercedesEngines.uk is part of the Engine Finders family, the UK's leading engine replacement marketplace - giving you the research depth of an independent authority with a vetted route to action when you need one.

GLS Frequently Asked Questions

1

How much does a GLS engine replacement cost in the UK?

A GLS engine replacement typically costs £1,800–£14,000 supply-only depending on engine type and condition. OM642 V6 diesel: £1,800–£3,200 reconditioned. M273 V8: £2,500–£5,000 reconditioned. M278 V8 biturbo: £3,500–£6,500 reconditioned. M157 AMG V8: £6,000–£10,000 reconditioned. M256, M176 and M177 units: £3,500–£14,000 reconditioned [PLACEHOLDER - confirm vs cost sheet]. Labour adds 12–24 hours at £65–£95/hr independent or £110–£160/hr dealer. Use our calculator above for a personalised estimate.
2

Which GLS engine is the most reliable?

The OM642 3.0 V6 diesel is the most reliable GLS engine - fitted to the GL 350 CDI (X164) and GLS 350d (X166). It's well-understood, parts are abundant, and while labour is intensive for jobs like the oil cooler seal, the engine itself is robust. The M176 4.0 V8 biturbo (X167) is also well-regarded, but it's too new for long-term data. Avoid the M278 V8 if you want low-maintenance ownership.
3

Which GLS engine should I avoid?

The M278 4.7 V8 biturbo in the X166 GL 500 / GLS 500 - timing chain stretch and turbocharger issues are well-documented on higher-mileage examples. Not all M278s fail, but the replacement cost (£3,500–£6,500) is significant. The M273 4.7 V8 in the X164 has fewer catastrophic failures but suffers from intake manifold runner flap issues. The OM642 diesel is the safest bet.
4

Is the GLS OM642 oil cooler seal issue real?

Yes - it's the most common GLS engine problem. The O-ring in the "V" of the engine fails, causing oil and coolant to mix. Symptoms: oil in the coolant expansion tank, oil level dropping, burning oil smell. Repair cost: £800–£1,500. Ignore it and it can lead to overheating and engine damage. Common on all OM642-equipped GL/GLS models - especially from 80,000–120,000 miles.
5

Is it worth replacing a GLS engine?

It depends entirely on generation and condition. An X164 GL 320 CDI worth £8,000–£10,000 - a £1,800–£3,200 reconditioned OM642 is viable (18–40% of vehicle value). An X166 GLS 500 worth £12,000–£18,000 - a £3,500–£6,000 M278 recon is a tougher call (30–50%). An X166 GLS 63 AMG worth £20,000–£35,000 - a £6,000–£10,000 M157 recon is still viable if the car is clean. Apply the 70% threshold: if replacement cost exceeds 70% of the car's value, get a scrap valuation first.
6

Which GLS generation should I buy?

The X166 facelift (2016–2019) with the OM642 diesel is the best GLS generation - post-facelift electronics, the GLS nameplate, better rust protection, and values that have already absorbed the steepest depreciation. The X164 is a bargain but ageing; the X167 is the best car but expensive. For the X166, avoid the M278 V8 unless the timing chain has been done; the OM642 is the smarter buy.
7

How do I find my GLS engine code?

The engine code is stamped on the engine block - look for a metal plate on the passenger side of the engine (left-hand side when viewed from the front). For the OM642, the code is visible on the front of the engine near the oil filter housing. You can also find the engine code in your V5C registration document, or by entering your VIN into an online Mercedes decoder. Not sure? Our diagnostic calculator can help identify your engine from your symptoms and vehicle details.
8

GLS vs GLE - which is more reliable?

The GLS and GLE share many engines (OM642, M278, M157, M256, M176), so reliability is almost identical on a like-for-like basis. The difference is the size and the price. The GLE is smaller, lighter, and cheaper to run; the GLS is larger, heavier, and more expensive. The GLE has slightly better fuel economy and lower running costs; the GLS offers genuine seven-seat capability. Buy on space requirements and budget, not reliability - both are robust if maintained.

Need a head-to-head comparison?

Read our in-depth Mercedes reliability comparison guides.

Read the Full Head-to-Head

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a Decision?

Everything you need to choose with confidence.
Data. Honesty. Specialists. All in one place.

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Generations

Compare the X164, X166 and X167, generation by generation, and find the right GLS for you. → Explore GLS Generations

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