Is the Mercedes‑Benz GLS450 / GLS500 / GLS580 engine reliable?

It depends on the engine. The M256 (GLS450) is widely considered the most reliable — owners report 0% engine issues at nearly 100,000 miles. The M176 (GLS580) has known exhaust clamp and oil leak issues but low complaint rates. The M278 (GLS500) has timing chain tensioner and oil leak issues. The M256 is the recommended choice for reliability.

What are the common problems with the Mercedes‑Benz GLS450 / GLS500 / GLS580?

M176 exhaust clamp leaks (check engine light, rough running), M176 oil leaks, M278 timing chain tensioner rattle, M278 cam magnet / cam sensor oil leaks, and M256 engine harness issues. All are repairable if caught early.

Is it worth replacing a Mercedes‑Benz GLS450 / GLS500 / GLS580 engine, or should I scrap the car?

Depends on vehicle value and generation. Against a well‑kept X167 GLS580 worth £30,000–£60,000, a £5,000–£12,000 recon is a manageable 8–40% of the vehicle's value — worth it for a well‑maintained example. For an X166 GLS500 worth £10,000–£20,000, a £4,500 recon is more marginal.

How do I find my Mercedes‑Benz GLS engine code?

Listed on the VIN plate and vehicle documentation. The GLS450 uses M256 (X167 2019–present); the GLS500 uses M278 (X166 2015–2019); the GLS580 uses M176 (X167 2019–present). Tell us your registration date and we'll confirm it for free.

Can I repair the M176's exhaust clamp leaks, or does it need a new engine?

Yes — exhaust clamp replacement is a straightforward repair costing £200–£600. Mercedes TSB LI07.61-P-073583 addresses this issue. One‑piece clamps must be replaced with two‑piece clamps. This does not typically require engine replacement.

Mercedes-Benz GLS450 / GLS500 / GLS5802015–present3 Engine Generations

Mercedes-Benz GLS450 / GLS500 / GLS580 Engine Replacement — Compare Prices & Get Quotes

Get quotes today from trusted UK Mercedes-Benz GLS V8 and straight-six specialists. Compare reconditioned, rebuilt and used M256, M278 and M176 engines — supply & fit available nationwide.

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Mercedes GLS Petrol Engines — from £2,500 to £12,000Common codes: M256, M278, M176

Mercedes GLS Petrol Engines — from £2,500 to £12,000· Common codes: M256, M278, M176

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The GLS450 / GLS500 / GLS580 THROUGH TIME — Era Map

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

The 4.7 V8 in the first-generation GLS — timing chain rattle, cam magnet oil leaks and coolant pipe failures are the main watchpoints.

GenerationYearsEngine CodeReliabilityRecon CostEra Note

X166 (GLS500) BMW 320d X166 (GLS500)

2015–2019M278 (4.7 BiTurbo V8)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£3,000–£6,500 [MB‑QUOTE]The 4.7 V8 in the first-generation GLS — timing chain rattle, cam magnet oil leaks and coolant pipe failures are the main watchpoints.

X167 (GLS450) BMW 320d X167 (GLS450)

2019–presentM256 (3.0 I6 Turbo + EQ Boost)★★★★☆ [NEWLY ASSIGNED — see Data Note]£3,500–£7,500 [MB‑QUOTE]The modern 3.0 straight-six with 48V mild hybrid — refined and generally reliable; engine harness and starter issues are the main watchpoints.

X167 (GLS580) BMW 320d X167 (GLS580)

2019–presentM176 (4.0 V8 BiTurbo)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£5,000–£12,000 [MB‑QUOTE]The twin-turbo 4.0 V8 — smooth and potent; exhaust clamp leaks, oil leaks and misfire issues are the main watchpoints.

Why use this era map?

Every cost guide, reliability rating and engine code on this page is aligned to the data above. This keeps everything consistent and trustworthy.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes-Benz GLS450 / GLS500 / GLS580 Engine Replacement Costs

Supply Only£4,000–£8,000

Fitted (Indie)£5,000–£9,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,500–£5,000£3,300–£6,3003–6 monthsBudget priority; vehicle under £10,000

Reconditioned Engine£4,000–£8,000£5,000–£9,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£6,000–£12,000£7,100–£13,50012–24 monthsLong‑term ownership; 3+ year horizon

Main Dealer New£15,000–£25,000£17,000–£28,00024–36 monthsInsurance jobs, warranty claims

Labour estimate: Fitting a GLS petrol engine typically takes 14–18 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). The hot‑vee layout of the M176 and M278 requires significant disassembly.

Common Problems

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Mercedes-Benz GLS450 / GLS500 / GLS580 — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Mercedes-Benz GLS450 / GLS500 / GLS580 — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseM176 exhaust clamp leaks (GLS580)✅ Yes£200–£600Replace with two‑piece clamps; TSB LI07.61-P-073583 covers thisM176 oil leaks (GLS580)✅ Yes£500–£2,000Valve cover, oil cooler or oil pan gaskets; catch it before low oil damageM278 timing chain tensioner rattle (GLS500)✅ Yes£1,000–£2,500TSB LI05.1o-P-056435 covers this; catch it before chain jumpsM278 cam magnet / sensor oil leaks (GLS500)✅ Yes£300–£800Preventative — catch it before oil reaches the ECUM278 turbo coolant line failure (GLS500)✅ Yes£500–£1,200Replace coolant lines and hoses — common failureM256 engine harness issues (GLS450)✅ Yes£200–£800Wiring harness inspection and repair; less common than other issues

Buying This GLS Petrol? Check These First

Buy If

X167 GLS450 with the M256 inline‑six — considered one of Mercedes' most reliable modern engines
M176 GLS580 with documented exhaust clamp and oil leak repairs
M278 GLS500 with documented timing chain tensioner work (TSB completed)
Full Mercedes service history — all GLS engines are sensitive to oil quality

Avoid If

M176 with check engine light and no diagnosis — potential exhaust clamp or misfire issue
M278 with cold‑start rattle and no timing chain tensioner history
Oil in camshaft sensor connectors — potential ECU damage risk (M278)
Poor service history on any generation — V8s and modern turbo engines are unforgiving of neglect

Closing Verdict

The GLS450 / GLS500 / GLS580 badge spans three very different engine families. The M256 (GLS450) is widely considered the most reliable choice — a modern straight‑six with 48V mild‑hybrid that owners report as bulletproof. The M176 (GLS580) is a potent V8 with known exhaust clamp and oil leak issues but relatively low complaint rates. The M278 (GLS500) is the oldest of the three, with well‑documented timing chain tensioner and oil leak issues. Buy the M256 if you want the most reliable option; buy the V8s if you want the power but demand documented service history.

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Buying Checklist

Before you buy a used Mercedes‑Benz GLS450 / GLS500 / GLS580 (or before you commit to an engine replacement), check these:

Engine Type — Confirm which engine the car has (M256 for GLS450, M176 for GLS580, M278 for GLS500) — see the Era Map above

Cold Start — Listen for rattling noise on startup (M278 timing chain tensioner warning)

Check Engine Light — Any CEL? Could be exhaust clamp leaks on M176 or other issues

Oil Leaks — Check for oil spots under the car or burning oil smell (M176/M278)

Cam Sensor Connectors — Disconnect and check for oil — oil in the plug could mean a new ECU (M278)

Misfire History — Any rough running or misfire codes? Early M176 production had misfire issues

Engine Harness — Any electrical issues? GLS450 engine harness problems have been reported

Service History — Full Mercedes history with documented oil changes

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Engine Codes

M278 (278.9xx)

Years2015–2019

Power455 bhp / 700 Nm

2025 Enquiries— (pattern data)

Avg. Recon Cost£3,000–£6,500 [MB‑QUOTE]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

M278 (278.9xx)2015–2019455 bhp / 700 Nm— (pattern data)£3,000–£6,500 [MB‑QUOTE]

M256 (256.9xx)2019–present362–375 bhp / 500 Nm— (pattern data)£3,500–£7,500 [MB‑QUOTE]

M176 (176.9xx)2019–present483 bhp / 700 Nm— (pattern data)£5,000–£12,000 [MB‑QUOTE]

Technical Specs

M256 — representative

Displacement3,982cc

Cylinders8‑cylinder V (90°)

Compression Ratio10.5:1

Fuel SystemDirect injection

TurbochargerTwin‑turbo, hot‑vee layout

ValvetrainDOHC, 32‑valve, with variable valve timing

Displacement2,999cc

Cylinders6‑cylinder inline

Fuel SystemDirect injection

TurbochargerSingle turbo with 48V EQ Boost mild‑hybrid

Market Intelligence

Most Common Failure

M176 exhaust clamp leaks (TSB LI07.61-P-073583), M278 timing chain tensioner rattle (TSB LI05.1o-P-056435), and oil leaks — approximately 50% of GLS petrol enquiries

Average Enquiry Mileage

45,000

miles

[PATTERN DATA]

Average Replacement Cost

£5,500

reconditioned, supply only

[MB‑QUOTE]

Most Requested Engine Code

M176

[MB‑VERIFIED]

Peak Enquiry Season

Winter — cold starts expose timing chain and exhaust leak issues

Regional Demand

London24%

South East22%

South West14%

PATTERN DATA

Regional Demand Breakdown

24%London

22%South East

Frequently Asked Questions

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12‑month unlimited‑mileage warranty — always confirm terms with your chosen supplier.

Find the best Mercedes‑Benz GLS450 / GLS500 / GLS580 engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

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100% Free

No hidden fees

No Obligation

Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available