Mercedes‑Benz S‑Class S320 CDI / S350 CDI / BlueTEC Engine Replacement — Compare Prices & Get Quotes
Get quotes today from trusted UK Mercedes‑Benz S‑Class diesel specialists. Compare reconditioned, rebuilt and used 3.2L straight‑six and 3.0L V6 turbo‑diesel engines — OM648 and OM642 variants across the W220, W221 and W222 generations — supply & fit available nationwide.
The S320 CDI / S350 CDI / BlueTEC THROUGH TIME — Era Map
Four generations. Four eras. One guide to reliability, costs and what really matters.
Era Note
3.2L straight‑six — 204 hp, 500 Nm; robust cast‑iron block; harmonic balancer and injector issues are the main 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 S320 CDI / S350 CDI / BlueTEC Engine Replacement Costs
Figures above reflect current S320 CDI / S350 CDI replacement costs. The OM642 V6 variant typically sits at the higher end of the range. See the Era Map above for generation‑specific pricing.
Labour estimate: Fitting an S320 CDI / S350 CDI engine typically takes 12–16 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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S‑Class S320 CDI / S350 CDI / BlueTEC — 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 S320 CDI / S350 CDI / BlueTEC? Check These First
Buy If
- W220 with the OM648 straight‑six (considered one of Mercedes' most robust diesel engines)
- OM642 (W221/W222) with oil cooler seals replaced with updated seals
- OM642 (W221/W222) with documented timing chain inspection or replacement
- Full service history with regular oil changes — both engines are sensitive to oil quality
- No cold‑start rattling (timing chain health)
- No oil leaks around the V of the engine (oil cooler seal health — OM642)
- No excessive NVH or booming noises (harmonic balancer health — OM648)
- Evidence of regular longer runs (DPF health — BlueTEC models)
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
- OM648 with excessive booming or droning noises — harmonic balancer may be failing
- No service history — both engines are unforgiving of neglect
- Engine warning light with no diagnosis — may indicate timing, injector or sensor problems
- BlueTEC models with AdBlue system faults — can be expensive to repair
Closing Verdict
The S320 CDI and S350 CDI / BlueTEC represent Mercedes‑Benz's flagship diesel S‑Class offerings across two generations. The W220 S320 CDI (1999–2005) uses the OM648.960 — a 3.2‑litre straight‑six with a cast‑iron block, widely considered one of Mercedes' most robust diesel engines. The OM648 is generally a very reliable engine — with proper maintenance, examples have reached 150,000+ miles with no injector issues, negligible oil consumption and excellent fuel economy. Common issues include harmonic balancer wear (causing NVH) and occasional injector/glow plug problems. The W221/W222 S350 CDI / BlueTEC (2006–2017) uses the OM642 — a 3.0‑litre V6 with an aluminium block, producing up to 258 hp and 620 Nm torque. The OM642 is a powerful and refined engine but has well‑documented vulnerabilities: oil cooler seal leaks, timing chain stretch, swirl flap failures, and SBC pump failures on early cars. The SBC (Sensotronic Brake Control) pump on early W221 models is a known weak point that can be expensive to replace. With typical S‑Class values ranging from £5,000 (W220) to £25,000+ (W222), an engine replacement is a major financial commitment — a well‑maintained W220 OM648 or a W222 OM642 with documented oil cooler seal and timing chain history is the safest choice.
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Buying Checklist
Before you buy a used Mercedes‑Benz S‑Class S320 CDI / S350 CDI / BlueTEC (or before you commit to an engine replacement), check these:
Cold Start — Listen for rattling or clattering (timing chain warning — both engines) — see the map above
Oil Leaks — Check around the V of the engine for oil cooler seal leaks (OM642)
Excessive NVH — Listen for booming, growling or droning noises (harmonic balancer wear — OM648)
Service History — Including which engine era (<a href='https://mercedesengines.uk/engine/om648'>OM648</a> or OM642) and oil‑change discipline
Timing Chain — Check for any chain work or cold‑start rattle
Injector Health — Check for smooth idle; any rough running may indicate injector issues
Glow Plugs — Check for hard starting; seized glow plugs are common on OM642
SBC Pump — For W221: check SBC pump health — can be an expensive repair
AdBlue System — For BlueTEC models: check for warning lights or AdBlue faults
Engine Warning Light — Have codes read; unresolved issues may indicate timing, injector 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.
OM648.960 (3.2L straight‑six)
Technical Specs
OM642.862 — W221/W222 S350 CDI BlueTEC→ Compare S320 CDI / S350 CDI engine prices for your S‑Class
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Market Intelligence
Most Common Failure (OM648 — W220)
Harmonic balancer wear and injector issues — the most frequent S320 CDI enquiries
Most Common Failure (OM642 — W221/W222)
Oil cooler seal leaks and timing chain stretch — the defining issues of the S350 CDI
Average Enquiry Mileage
60,000
–90,000 miles
[PATTERN DATA]
Average Replacement Cost
£4,500
–£6,000 reconditioned, supply only
[PLACEHOLDER]
Most Requested Engine Code
OM642 / OM648
[PATTERN DATA]
Peak Enquiry Season
Winter — cold starts expose timing chain 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.
Why UK Mercedes‑Benz S320 CDI / S350 CDI / BlueTEC Owners Trust MercedesEngine.uk
Trusted S‑Class Diesel Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real S320 CDI and S350 CDI owners, as part of the Engine Finders network, across every engine era — OM648 and OM642 — covering the W220, W221 and W222 generations.
Compare S‑Class Diesel Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit. We cover the 3.2L straight‑six and 3.0L V6 turbo‑diesels specifically, with specialists who understand the OM648's robust reliability, OM642 oil cooler seal and timing chain vulnerabilities, and the unique requirements of the S‑Class.
UK Engine Replacement Services for S‑Class Diesel
supply‑only or full supply & fit available nationwide, covering every generation of this badge since 1999, with a 12‑month warranty as standard across our network.
Find the best Mercedes‑Benz S320 CDI / S350 CDI / BlueTEC engine replacement UK owners rely on. Compare prices from trusted specialists on EnginesMarket today and get your S‑Class 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