Mercedes‑Benz GLS350d / GLS400d Engine Replacement — Compare Prices & Get Quotes
Get quotes today from trusted UK Mercedes‑Benz GLS diesel specialists. Compare reconditioned, rebuilt and used 3.0‑litre V6 and straight‑six turbo‑diesel engines — OM642 and OM656 variants across the X166 and X167 generations — supply & fit available nationwide.
The GLS350d / GLS400d THROUGH TIME — Era Map
Four generations. Four eras. One guide to reliability, costs and what really matters.
Era Note
3.0L V6 turbo‑diesel — 258 bhp, 620 Nm; oil cooler seals and timing chain stretch are the critical watch items
Why use this era map?
This table is the single source every other section on this page matches — Sections 2, 4 and 6 reference it rather than restating conflicting figures.
Mercedes‑Benz GLS350d / GLS400d Engine Replacement Costs
Figures above reflect current GLS diesel replacement costs. The OM656 variant typically sits at the higher end of the range. See the Era Map above for generation‑specific pricing.
Labour estimate: Fitting a GLS diesel engine typically takes 14–18 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). The OM642 oil cooler seal replacement is particularly labour‑intensive as many ancillary parts must be removed to access the cooler in the V of the engine.
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GLS350d / GLS400d — 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?
Buying This GLS Diesel? Check These First
Buy If
- X167 (2019+) with the OM656 straight‑six (more powerful and refined)
- OM642 (X166) with oil cooler seals replaced with updated purple seals
- OM642 (X166) with documented timing chain inspection or replacement
- OM656 (X167) with camshaft and rocker condition verified
- Full service history with regular oil changes — both engines are sensitive to oil quality
- No cold‑start rattling (timing chain health — OM642)
- No tapping or popping noises (camshaft/rocker health — OM656)
- No oil leaks around the V of the engine (oil cooler seal health — OM642)
- Evidence of regular longer runs (DPF health — both engines)
Avoid If
- OM642 with cold‑start rattle and no chain history — assume it's overdue
- OM642 with oil leaks in the V of the engine — oil cooler seals may be failing
- OM656 with tapping or popping noises — camshaft/rocker wear may be developing
- No service history — both engines are unforgiving of neglect
- Short‑journey ownership history — DPF and EGR issues likely
- Engine warning light with no diagnosis — may indicate timing, turbo, emission or sensor problems
Closing Verdict
The GLS350d and GLS400d are Mercedes‑Benz's flagship three‑row SUVs — offering space, luxury and powerful diesel engines. The X166 GLS350d (2013–2019) uses the OM642 3.0‑litre V6 — a widely used and generally reliable engine when properly maintained. However, it has well‑documented vulnerabilities: oil cooler seal leaks (labour‑intensive to repair) and timing chain stretch. The X167 GLS400d (2019–present) uses the OM656 3.0‑litre straight‑six — a more powerful and refined engine producing 330 bhp and 700 Nm torque. The OM656 is generally considered reliable, but owners have reported camshaft and rocker wear around 100,000 miles, and emission system issues. With typical GLS values ranging from £25,000 (X166) to £60,000+ (X167), an engine replacement is a major financial commitment — a well‑maintained X167 OM656 with full service history is the safest choice, but a well‑maintained X166 with documented oil cooler seal and timing chain history can also serve well.
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Buying Checklist
Before you buy a used Mercedes‑Benz GLS350d / GLS400d (or before you commit to an engine replacement), check these:
Cold Start — Listen for rattling or clattering (timing chain warning — OM642) — see the map above
Tapping/Popping Noises — Listen for tapping or popping (camshaft/rocker wear — OM656)
Oil Leaks — Check around the V of the engine for oil cooler seal leaks (OM642)
Service History — Including which engine era (OM642 or OM656) and oil‑change discipline
Timing Chain — For OM642 (X166): check for any chain work or cold‑start rattle
EGR System — Check for any loss of power or warning lights; EGR clogging is common
DPF Regeneration — Check history; short journeys accelerate wear on all diesel eras
AdBlue System — Check for warning lights or AdBlue faults (both engines)
Engine Warning Light — Have codes read; unresolved issues may indicate timing, turbo, emission or sensor problems
MOT History — Check for emissions‑related failures
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
Technical Specs
OM656 — X167 GLS400d→ Compare GLS350d / GLS400d engine prices for your GLS
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Market Intelligence
Most Common Failure (OM642 — X166)
Oil cooler seal leaks and timing chain stretch — the defining issues of the GLS350d
Most Common Failure (OM656 — X167)
Camshaft/rocker wear and emission system issues — the primary concerns of the GLS400d
Average Enquiry Mileage
50,000
–80,000 miles
[PATTERN DATA]
Average Replacement Cost
£5,000
–£6,500 reconditioned, supply only
[PLACEHOLDER]
Most Requested Engine Code
OM656
[PATTERN DATA]
Peak Enquiry Season
Winter — cold starts expose timing chain and camshaft wear
[PATTERN DATA]
Regional Demand
PATTERN DATA
Regional Demand Breakdown
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 condition, 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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Trusted GLS Diesel Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real GLS350d and GLS400d owners, as part of the Engine Finders network, across every engine era — OM642 and OM656 — covering the X166 and X167 generations.
Compare GLS Diesel Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit. We cover the 3.0‑litre V6 and straight‑six turbo‑diesels specifically, with specialists who understand the OM642 oil cooler seal and timing chain vulnerabilities, OM656 camshaft/rocker wear, and the unique requirements of the GLS.
UK Engine Replacement Services for GLS Diesel
supply‑only or full supply & fit available nationwide, covering every generation of this badge since 2013, with a 12‑month warranty as standard across our network.
Find the best Mercedes‑Benz GLS350d / GLS400d engine replacement UK owners rely on. Compare prices from trusted specialists on EnginesMarket today and get your GLS back on the road with confidence.
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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