How much does a Mercedes GLC 350d / 400d engine replacement cost in the UK?

A reconditioned GLC 350d (OM642) engine typically costs £3,500–£6,500 supply only, while a GLC 400d (OM656) engine costs £5,000–£8,500. Fitting adds £2,000–£3,500 depending on location and workshop rates. A replacement OM642 engine costs on average £5,474 in good condition, with new or reconditioned engines costing up to £15,036. Main dealer new engines start from £12,000–£18,000+ supply only. Use our calculator for a figure specific to your car.

Is the Mercedes GLC 350d / 400d engine reliable?

It depends on which engine your GLC has. The OM642 (GLC 350d, 2016–2019) is a proven V6 but has well-documented oil cooler seal leaks and swirl flap issues. The OM656 (GLC 400d, 2019–2023) is generally considered reliable, but early models suffer from vacuum pump failure (25–40k miles), camshaft rocker wear, and emissions system vulnerabilities. Check the Era Map above for your specific engine.

What are the common problems with the Mercedes GLC 350d / 400d?

Oil cooler seal leaks on the OM642 V6 — a labour-intensive repair costing up to £1,500+, vacuum pump failure on early OM656 engines (25–40k miles) requiring engine-out replacement, swirl flap and turbocharger issues on the OM642, and EGR/DPF/AdBlue system problems on both engines.

Is it worth replacing a Mercedes GLC 350d / 400d engine, or should I scrap the car?

Depends on vehicle value and condition. Against a well-kept £12,000–£25,000 GLC, a £4,500–£6,500 recon is 25–55% of the car's value. For a clean example with full service history, replacement is often worth it given the GLC's strong retained values. However, if the car has other issues (electrical faults, accident damage), evaluate total repair costs before committing.

How do I find my Mercedes GLC 350d / 400d engine code?

Listed on the VIN plate and vehicle documentation. As a rule of thumb: GLC 350d (2016–2019) has the OM642 (3.0L V6 diesel, 258 hp); GLC 400d (2019–2023) has the OM656 (2.9L straight-six diesel, 330 hp). Tell us your registration date and we'll confirm it for free.

Is the OM656 vacuum pump issue covered by warranty?

The vacuum pump failure on early OM656 engines typically occurs between 25–40k miles. If the vac pump issue hasn't happened yet, it won't, as it was always in that mileage region. Check with your dealer whether your vehicle is affected. If not covered, replacement is an engine-out job costing £1,500–£3,000+. A recall for driveshaft wear affecting 2017–2019 Mercedes models including the GLC has also been issued.

Mercedes GLC 350d / 400d2016–20232 Engine Generations (OM642 & OM656)

Mercedes GLC 350d / 400d Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes GLC 350d/400d UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes GLC specialists. The 350d and 400d badges span two diesel engine generations — the proven V6 OM642 and the refined straight-six OM656 — compare reconditioned, rebuilt and used engines with supply & fit available nationwide.

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Mercedes GLC 350d / 400d Engines — from £1,500 to £15,000+Common codes: OM642, OM656

Mercedes GLC 350d / 400d Engines — from £1,500 to £15,000+· Common codes: OM642, OM656

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Mercedes GLC 350d / 400d — Which Engine Does Your Car Actually Have?

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

Era Note

3.0L V6 twin-turbo — 258 hp, 620 Nm. Proven but ageing design; oil cooler seals, swirl flaps and turbo issues documented

GenerationYearsEngine CodeReliabilityRecon CostEra Note

X253/C253 (GLC 350d) BMW 320d X253/C253 (GLC 350d)

2016–2019OM642 (3.0L V6)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£3,500–£6,500 [MB-QUOTE]3.0L V6 twin-turbo — 258 hp, 620 Nm. Proven but ageing design; oil cooler seals, swirl flaps and turbo issues documented

X253/C253 (GLC 400d) BMW 320d X253/C253 (GLC 400d)

2019–2023OM656 (2.9L I6)★★★☆☆ [NEWLY ASSIGNED — see Data Note]£5,000–£8,500 [MB-QUOTE]2.9L straight-six twin-turbo — 330 hp, 700 Nm. Modern replacement for OM642; emissions system and vacuum pump concerns

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 GLC 350d / 400d Engine Replacement Costs

Supply Only£3,500–£7,500

Fitted (Indie)£5,500–£9,500

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,500–£3,500£2,500–£5,0001–6 monthsBudget priority; lower-mileage donor

Reconditioned Engine£3,500–£7,500£5,500–£9,50012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£5,000–£9,500£7,000–£11,50012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer New£12,000–£18,000+£14,000–£20,000+24–36 monthsInsurance jobs, warranty claims

Labour estimate: Fitting a GLC diesel engine typically takes 14–18 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). The OM642 oil cooler seal repair is particularly labour-intensive — located within the V of the engine, requiring significant disassembly.

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Common Problems

1. Oil Cooler Seal Leaks (OM642 V6)

Symptoms: Oil spots under the car, burning oil smell from engine bay, low oil level warning, visible oil residue in the V of the engine

Typical mileage: 60,000–120,000 miles — seals degrade over time

Repair cost: £800–£1,500+ (oil cooler seal replacement — labour-intensive as the cooler is located within the V of the engine)

Replacement cost: £5,500–£9,500 (if ignored — oil loss can cause engine damage)

🟠 Check - book inspection urgently if you notice oil spots or burning smell

Our recommendation:

The oil cooler seals on the OM642 V6 engine are a well-documented weakness. When they degrade, they cause oil to leak from the oil cooler, which is located within the V of the engine beneath a host of ancillary parts that must be removed before the cooler can be accessed — hence the high labour cost. The "laundry list of expensive problems" on the OM642 means repair costs often wipe out any fuel savings. If you notice oil spots or a burning smell, have the oil cooler seals inspected promptly. A £800–£1,500 repair is far cheaper than a £5,500–£9,500 engine replacement.

Read the full oil cooler seal failure guide → /failures/om642-oil-cooler-seals/ [NEW FAILURE PAGE NEEDED]

1. Oil Cooler Seal Leaks (OM642 V6)

Symptoms: Oil spots under the car, burning oil smell from engine bay, low oil level warning, visible oil residue in the V of the engine

Typical mileage: 60,000–120,000 miles — seals degrade over time

Repair cost: £800–£1,500+ (oil cooler seal replacement — labour-intensive as the cooler is located within the V of the engine)

Replacement cost: £5,500–£9,500 (if ignored — oil loss can cause engine damage)

🟠 Check - book inspection urgently if you notice oil spots or burning smell

Our recommendation:

Read the full oil cooler seal failure guide → /failures/om642-oil-cooler-seals/ [NEW FAILURE PAGE NEEDED]

2. Vacuum Pump Failure (OM656 Early Models)

Symptoms: Loss of braking assistance, vacuum system warning lights, rough running, engine warning light

Typical mileage: 25,000–40,000 miles — a known weakness on early OM656 engines

Repair cost: £1,500–£3,000+ (tandem oil and vacuum pump replacement — engine-out job)

Replacement cost: £5,000–£9,500 (if ignored — engine damage)

🔴 Immediate - if the vacuum pump fails, braking assistance is lost; book an inspection today

Our recommendation:

The OM656 has a known issue with the tandem oil and vacuum pump failing. If the vac pump issue hasn't happened yet, it won't, as it was always in the 25-40k region. The repair is significant — the pump failure "at a minimum requires engine out to replace, along with all the associated vacuum components". If you experience any vacuum system warnings or loss of braking assistance, stop driving immediately and arrange recovery.

Read the full vacuum pump failure guide → /failures/om656-vacuum-pump/ [NEW FAILURE PAGE NEEDED]

3. Swirl Flap & Turbocharger Issues (OM642)

Symptoms: Loss of power, rough running, black smoke from exhaust, engine warning light, rattling from the intake manifold

Typical mileage: 60,000–120,000 miles

Repair cost: £500–£1,200 (swirl flap repair or intake manifold replacement) / £1,500–£3,500 (turbocharger rebuild or replacement)

Replacement cost: £5,500–£9,500 (if ignored — full engine replacement)

🟠 Check - book inspection urgently if you experience power loss or smoke

Our recommendation:

The OM642 V6 is known for swirl flap actuator failure and turbocharger issues. Swirl flap rods can jam or break completely, while turbocharger problems can lead to power loss and black smoke. If you experience loss of power, rough running, or black smoke, have the swirl flap system and turbocharger inspected immediately.

Read the full swirl flap failure guide

4. EGR, DPF & AdBlue System Problems (OM656 & OM642)

Symptoms: Engine warning light, reduced performance, DPF warning, AdBlue countdown warning, limp mode

Typical mileage: Any mileage — short journeys accelerate the issue

Repair cost: £300–£800 (forced DPF regeneration / EGR cleaning) / £1,000–£2,500 (DPF or EGR replacement) / £500–£1,500 (AdBlue system repair)

Replacement cost: N/A — repair only (does not progress to engine replacement if addressed)

🟠 Check - book inspection urgently if warning appears

Our recommendation:

Both the OM642 and OM656 suffer from emissions system problems. EGR valves can become clogged, DPFs can block from short urban journeys, and AdBlue systems can fail. The OM656 is particularly sensitive to poor fuel quality and short journeys. If you primarily drive short distances, factor in regular motorway runs to allow passive DPF regenerations. If a warning appears, book a forced regeneration or system inspection immediately. Do not ignore AdBlue countdown warnings — they can prevent the car from starting.

Read the full AdBlue system failure guide

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GLC 350d / 400d — 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.

GLC 350d / 400d — 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 SenseOil cooler seal leak (OM642)✅ Yes£800–£1,500Labour-intensive but viable on well-maintained examplesVacuum pump failure (OM656 early)✅ Yes£1,500–£3,000+Engine-out job — viable if caught earlySwirl flap / turbo failure (OM642)✅ Yes£500–£3,500Catch early to prevent engine damageEGR / DPF / AdBlue system issues✅ Yes£300–£2,500Catch early to prevent more serious emissions system damageTiming chain failure❌ Usually NoEngine replacementFull engine replacement is the only reliable fix

Buying This GLC 350d / 400d? Check These First

Buy If

Post-2019 OM656-engined GLC 400d (with vacuum pump issue resolved — check if the car is beyond 40k miles)
Documented oil cooler seal replacement on OM642-engined GLC 350d
Full service history with regular oil changes using MB-approved oil
Evidence of regular motorway driving (DPF health)
No AdBlue or DPF warnings

Avoid If

Early OM656 (2019) with no vacuum pump history — the 25–40k mile failure window is a concern
OM642 with oil leaks from the V of the engine — this indicates oil cooler seal failure
Poor service history — these are complex diesel engines that need proper maintenance
AdBlue countdown warnings — may indicate expensive system failure
Check engine light with emissions-related codes

Closing Verdict

The GLC 350d and 400d represent two generations of Mercedes diesel engineering. The OM642 (350d, 2016–2019) is a proven V6 with a strong reputation, but it has well-documented weaknesses: oil cooler seal leaks (labour-intensive and costly), swirl flap and turbo issues. The OM656 (400d, 2019–2023) is a modern straight-six with impressive performance — 330 hp and 700 Nm — but early models suffered from vacuum pump failures and emissions system vulnerabilities. Buy a well-maintained example with full service history and no warning lights. On the OM656, check that the vacuum pump issue has been addressed. On the OM642, check for oil leaks and swirl flap health. Buy on documented history, not on price alone.

Don't guess.Get the right engine at the right price.

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Buying Checklist

Before you buy a used Mercedes GLC 350d or 400d (or before you commit to an engine replacement), check these:

Cold Start — Listen for rattling or unusual noises (timing chain / vacuum pump warning)

Oil Leaks — Look for oil residue in the V of the engine (OM642 oil cooler seals)

Service History — Including which engine (OM642 or OM656) and confirmed oil-interval discipline

AdBlue System — Any countdown warnings or engine management lights?

DPF Health — Check for DPF warning lights; short journeys are a red flag

Turbo Health — Listen for whistling; check for power loss or black smoke

Engine Warning Light — Have codes been read? Look for emissions-related codes

Recall Check — Check for driveshaft recall (2017–2019 models)

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

This table's rows match Section 1B's Era Map exactly.

OM642 (3.0L V6)

Years2016–2019

Power258 hp (190 kW) / 620 Nm

2025 Enquiries— (pattern data)

Avg. Recon Cost£3,500–£6,500【MB-QUOTE】

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

OM642 (3.0L V6)2016–2019258 hp (190 kW) / 620 Nm— (pattern data)£3,500–£6,500【MB-QUOTE】

OM656 (2.9L I6)2019–2023330 hp (243 kW) / 700 Nm— (pattern data)£5,000–£8,500【MB-QUOTE】

Technical Specs

OM656 — GLC 400d

Displacement2,987 cc (3.0L)

Cylinders6-cylinder V-engine

Valves24V

ChargeTurbo

Mixture formationCommon Rail

Power190 kW (258 hp)

Torque620 Nm

Displacement2,925 cc (2.9L)

Cylinders6-cylinder inline

ValvetrainDOHC, 4 valves per cylinder

Fuel SystemCommon-rail direct injection

TurbochargerTwin-turbo (BiTurbo)

Power243 kW (330 hp)

Torque700 Nm

0-62 mph5.6 seconds

Top Speed155 mph (limited)

→ Compare GLC 350d / 400d engine prices for your Mercedes

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Market Intelligence

Most Common Failure

Oil cooler seal leaks on OM642 V6 (labour-intensive repair); vacuum pump failure on early OM656 (25–40k miles)

Average Enquiry Mileage

40,000

–80,000 miles【PATTERN DATA】

Average Replacement Cost

£4,500

–£6,500 reconditioned, supply only【MB-QUOTE】

Most Requested Engine Code

OM642 (GLC 350d)【PATTERN DATA】

Peak Enquiry Season

Winter — cold starts expose vacuum pump and emissions issues【PATTERN DATA】

Regional Demand

London22%

South East18%

North West (12%)【PATTERN DATA】

Regional Demand Breakdown

22%London

18%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.

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