What are the common problems with the Mercedes S‑Class S280 / S320 / S350 / S420 petrol?

M104 head gasket failure (S280/S320), M104 fan bracket bearing failure and rear main seal leaks (S280/S320), M112 oil leaks from breather and valve covers (S350), M113 timing chain tensioner wear and oil leaks (S420), and W220 platform issues (early 2000–2002 cars). See the Era Map above for generation‑specific advice.

How do I find my Mercedes S‑Class S280 / S320 / S350 / S420 petrol engine code?

Listed on the VIN plate and vehicle documentation. As a rule of thumb: W140 S280 (1993–1998) = M104.944 (2.8L, 193 bhp); W140 S320 (1991–1998) = M104 (3.2L, 231 bhp); W220 S350 (2003–2005) = M112 (3.7L, 245 bhp); W220 S420 (1999–2005) = M113 (4.3L, 279 bhp). The W140 S320 was originally badged as 300SE/SEL before the naming change. Tell us your registration date and we'll confirm it for free.

Can I repair the M104 head gasket, or does it require engine replacement?

Yes — if caught early. A head gasket replacement costs £1,500–£2,500. The M104's head gasket is a routine maintenance item on higher‑mileage engines due to the aluminium head and cast‑iron block expanding at different rates. If the engine has overheated severely, the head may be cracked or warped, requiring a full engine replacement (£3,000–£6,000). At the first sign of oil leaks or coolant loss, book an inspection immediately.

Mercedes S‑Class S280 / S320 / S350 / S420 Petrol1993–2005M104 / M112 / M113 / M119

Mercedes S‑Class S280 / S320 / S350 / S420 Petrol Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes S‑Class Petrol UK Engine Enquiry Data 2025
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Mercedes S‑Class S280 / S320 / S350 / S420 Petrol Engines — from £2,000 to £10,000Common codes: M104, M112, M113, M119

Mercedes S‑Class S280 / S320 / S350 / S420 Petrol Engines — from £2,000 to £10,000· Common codes: M104, M112, M113, M119

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The S‑CLASS S280 / S320 / S350 / S420 PETROL THROUGH TIME — Era Map

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

Era Note

M104 straight‑six — smooth, durable, capable of 200,000+ miles; head gasket failure is the defining weakness

GenerationYearsEngine CodeReliabilityRecon CostEra Note

S‑Class W140 (S280) BMW 320d S‑Class W140 (S280)

1993–1998M104.944 (2.8L I6, 193 bhp)★★★½☆ [NEWLY ASSIGNED — see Data Note]£3,000–£5,500 [PLACEHOLDER — confirm vs cost sheet]M104 straight‑six — smooth, durable, capable of 200,000+ miles; head gasket failure is the defining weakness

S‑Class W140 (S320) BMW 320d S‑Class W140 (S320)

1991–1998M104 (3.2L I6, 231 bhp)★★★½☆ [NEWLY ASSIGNED — see Data Note]£3,200–£6,000 [PLACEHOLDER — confirm vs cost sheet]Larger M104 — 231 bhp, 315 Nm; same head gasket vulnerability; fan bracket bearing and rear main seal leaks also common

S‑Class W220 (S350) BMW 320d S‑Class W220 (S350)

2003–2005M112 (3.7L V6, 245 bhp)★★★★☆ [NEWLY ASSIGNED — see Data Note]£3,500–£6,500 [PLACEHOLDER — confirm vs cost sheet]M112 V6 — considered one of Mercedes' most reliable engines; oil leaks from breather covers and valve covers are the main watchpoints

S‑Class W220 (S420) BMW 320d S‑Class W220 (S420)

1999–2005M113 (4.3L V8, 279 bhp)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,000–£7,500 [PLACEHOLDER — confirm vs cost sheet]M113 V8 — "about the most reliable engine MB made"; timing chain tensioner wear and oil leaks are the key concerns

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.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes S‑Class S280 / S320 / S350 / S420 Petrol Engine Replacement Costs

Supply Only£3,500–£6,500

Fitted (Indie)£4,500–£8,000

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,000–£4,000£2,800–£5,2001–6 monthsBudget priority; finding a good donor M104/M112/M113 is becoming harder

Reconditioned Engine£3,500–£6,500£4,500–£8,00012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£5,000–£10,000£6,200–£12,00012–24 monthsLong‑term ownership; full factory‑spec refresh

Main Dealer NewN/A — unavailableN/A—These engines are no longer produced new; reconditioned units are the standard

Figures above reflect the W140 and W220 petrol era (1993–2005). Reconditioned engines typically cost £1,200–£2,200 supply only, with total installed costs around £1,800–£2,800 for standard engines. A Mercedes head gasket replacement on the M104 can cost a couple of thousand pounds. Buyers should allocate around £2,500 for a new head gasket on the M104.

Labour estimate: Fitting an S‑Class petrol engine typically takes 10–14 hours at £85–£130/hr (independent) or £140–£200/hr (London/SE dealer). The M104's inline‑six is reasonably accessible, while the M112 and M113 V configurations add some complexity. [PLACEHOLDER — confirm vs cost sheet]

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Common Problems

1. M104 Head Gasket Failure (S280, S320 — W140)

Symptoms: External oil leak at the front of the engine where the timing chain cover meets the head, oil pooling on the garage floor, oil burning on the exhaust manifold causing smoke at start‑up, coolant loss, overheating, oil in coolant or coolant in oil.

Typical mileage: 100,000–200,000 miles — can occur at any mileage but becomes more common with age

Repair cost: £1,500–£2,500 (head gasket replacement)

Replacement cost: £3,000–£6,000 (if head is cracked or warped)【PLACEHOLDER】

🔴 Immediate - if you notice oil leaks, coolant loss or overheating, book an inspection today

Our recommendation:

The M104's head gasket is the defining weakness of this otherwise legendary engine. The aluminium head and cast‑iron block expand at different rates under heat cycling, making the head gasket the sacrificial item. This is not a design failure but a consequence of physics — however, it means that head gasket replacement is a routine maintenance item on higher‑mileage M104 engines. The leak is typically external, with oil seeping from the front timing cover area. In severe cases, oil can pool on the garage floor or burn on the exhaust manifold. At the first sign of oil leaks, have the head gasket inspected. Allow around £2,500 for replacement. Some owners recommend letting the car warm up for a few minutes before driving to extend head gasket life.

1. M104 Head Gasket Failure (S280, S320 — W140)

Typical mileage: 100,000–200,000 miles — can occur at any mileage but becomes more common with age

Repair cost: £1,500–£2,500 (head gasket replacement)

Replacement cost: £3,000–£6,000 (if head is cracked or warped)【PLACEHOLDER】

🔴 Immediate - if you notice oil leaks, coolant loss or overheating, book an inspection today

Our recommendation:

2. M104 Fan Bracket Bearing Failure (S280, S320 — W140)

Symptoms: Unusual noises from the front of the engine, fan touching the water pump, overheating, loud grinding or squealing.

Typical mileage: 250,000 km (approximately 155,000 miles)

Repair cost: £200–£600 (fan bracket bearing replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless overheating leads to engine damage)

🟠 Check - book inspection urgently if unusual noises occur

Our recommendation:

The fan bracket bearing on the M104 can fail, typically around 250,000 km. When it fails, the fan can touch the water pump, causing further damage. If you hear unusual noises from the front of the engine, have the fan bracket bearing inspected immediately. Replacement is relatively straightforward but should not be delayed.

3. M104 Rear Main Seal Leak (S280, S320 — W140)

Symptoms: Oil spots under the vehicle, oil around the transmission bellhousing, burning oil smell, gradual oil loss.

Typical mileage: 100,000–200,000 miles

Repair cost: £300–£900 (rear main seal replacement — transmission removal required)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless oil starvation leads to engine damage)

🟡 Monitor - book inspection soon; monitor oil levels regularly

Our recommendation:

Rear main seal oil leaks are very common on the M104. They typically present as a gradual slow leak that doesn't get progressively worse, rather than a sudden failure. However, if left unchecked, oil loss can lead to engine damage. Monitor oil levels regularly and have the seal inspected if you notice oil spots.

4. M112 Oil Leaks (S350 — W220)

Symptoms: Oil spots under the vehicle, burning oil smell, visible oil seepage from the top of the engine, oil in spark plug wells.

Typical mileage: 60,000–120,000 miles

Repair cost: £300–£900 (breather cover and valve cover gasket replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only

🟡 Monitor - book inspection soon; oil leaks can damage other components

Our recommendation:

The M112 V6 is considered one of Mercedes' most reliable engines, but it does suffer from oil leaks. The most common areas are the breather covers on the top of the engine (also known as cambox covers), valve covers, and the oil filter housing. The breather cover oil leaks can cause oil to puddle in the spark plug wells and drip onto the hot manifold, creating smoke. If you notice oil spots or a burning smell, have the system inspected promptly. Resealing the breather covers is a tedious but straightforward job using high‑temperature automotive sealant.

5. M113 Timing Chain Tensioner Wear (S420 — W220)

Symptoms: Rattling noise on cold start, metallic clattering from the front of the engine, engine warning light, loss of power, rough running.

Typical mileage: 80,000–150,000 miles

Repair cost: £800–£1,500 (timing chain tensioner replacement)【PLACEHOLDER】

Replacement cost: £4,000–£7,500 (if timing chain skips and valves meet pistons)【PLACEHOLDER】

🔴 Immediate - if you hear rattle, book an inspection today

Our recommendation:

The M113 V8 is one of Mercedes' most reliable engines — "about the most reliable engine MB made" — but the timing chain tensioner can fail with age. A rattling noise on cold start is the primary symptom, caused by the spring that keeps tension until oil pressure builds up failing. The tensioner itself is a combination of a hollow bolt with a piston insert, a spring and a ratchet that maintains piston position in the absence of oil pressure. At the first sign of cold‑start rattle, have the tensioner inspected. Replacement is not a difficult job.

6. M113 Oil Leaks (S420 — W220)

Symptoms: Oil spots under the vehicle, burning oil smell, visible oil seepage from valve covers, oil cooler seals or front crankshaft seal.

Typical mileage: 60,000–120,000 miles

Repair cost: £300–£1,200 (gasket replacement)【PLACEHOLDER】

Replacement cost: N/A — repair only (unless oil starvation leads to engine damage)

🟡 Monitor - book inspection soon; oil leaks can damage other components

Our recommendation:

Oil leaks are a common concern for the M113 engine, often stemming from worn gaskets or seals. The most frequently affected areas include valve cover gaskets, oil filter housing gaskets, and the front crankshaft seal. The M113 V8 is known for developing slow leaks over time. If you notice oil spots or a burning smell, have the system inspected promptly. Regular seal replacements are part of the cost of running an M113‑equipped vehicle.

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Mercedes S‑Class S280 / S320 / S350 / S420 Petrol — 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 S‑Class S280 / S320 / S350 / S420 Petrol — 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 SenseM104 head gasket failure✅ Yes£1,500–£2,500Essential maintenance on higher‑mileage M104s; catch it before head damageM104 fan bracket bearing✅ Yes£200–£600Straightforward replacement; catch it before further damageM104 rear main seal leak✅ Yes£300–£900Labour‑intensive but essential; catch it before oil starvationM112 oil leaks (breather/valve covers)✅ Yes£300–£900Affordable preventative maintenanceM113 timing chain tensioner wear✅ Yes£800–£1,500Catch it early — far cheaper than engine damageM113 oil leaks✅ Yes£300–£1,200Affordable preventative maintenanceMajor engine mechanical failure❌ RareEngine replacementThese engines are robust; catastrophic failures are rare

Buying This S‑Class Petrol? Check These First

Buy If

Full service history with regular oil changes using Mercedes‑approved oil
M104 (S280/S320): head gasket replaced or inspected (allow £2,500 for this work if not done)
M104 (S280/S320): fan bracket bearing in good condition
M112 (S350): no oil leaks from breather covers or valve covers
M113 (S420): timing chain tensioner replaced or functioning correctly
W220 (2003+) facelift cars are more reliable than early (2000–2002) cars
Low mileage (sub‑100,000 miles) and well‑maintained

Avoid If

No proof of regular maintenance — these engines are durable but unforgiving of neglect
M104 with significant oil leaks — head gasket work is imminent
M104 with overheating history — potential head damage
M112 with extensive oil leaks — multiple gaskets may need replacement
M113 with cold‑start rattle — timing chain tensioner work is imminent
Early W220 (2000–2002) cars — the platform is considered one of the worst ever built
"Cheap" examples — the purchase price is the least of your worries

Closing Verdict

The Mercedes S‑Class S280, S320, S350 and S420 petrol represent a golden era of Mercedes engineering — over‑engineered, built to last, and powered by some of the most celebrated engines ever made. The M104 straight‑six is smooth and durable but demands head gasket vigilance. The M112 V6 is "almost indestructible", while the M113 V8 is "about the most reliable engine MB made". The W140 is a classic — over‑engineered and built to last, but with complex electronics and air suspension that can be expensive to maintain. The W220 is more modern but early cars (2000–2002) are considered problematic. Buy on service history, prioritise facelift W220 cars (2003+) or well‑maintained W140s, and budget for preventative maintenance. As one owner put it: "The M113 AMG 5.5 is about the most reliable engine MB made. Unfortunately the W220 (especially 2000-02) platform is one of the worst ever built".

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Buying Checklist

Before you buy a used Mercedes S‑Class S280, S320, S350 or S420 petrol (or before you commit to an engine replacement), check these:

M104 Head Gasket (S280/S320) — Any oil leaks from the front of the engine or oil pooling? Any coolant loss? (allow £2,500 for this work)

M104 Fan Bracket (S280/S320) — Any unusual noises from the front of the engine?

M104 Oil Level (S280/S320) — Check dipstick; any oil loss indicates rear main seal or head gasket issues

<a href='https://mercedesengines.uk/engine/m112'>M112</a> Oil Leaks (S350) — Check for oil around the top of the engine (breather covers, valve covers)

M113 Timing Chain (S420) — Any cold‑start rattle? Timing chain tensioner may be failing

M113 Oil Leaks (S420) — Check for oil around valve covers and oil filter housing

W220 Platform — Early (2000–2002) cars have more issues than facelift (2003+) cars

Engine Warning Light — Have codes been read? Head gasket, timing, or oil leak codes are most common

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 exactly match Section 1B's Era Map — the same engine codes, years, and generation coverage.

M104.944 (S280)

Years1993–1998

Power193 bhp (142 kW) @ 5,500 rpm · 270 Nm @ 3,750 rpm

2025 Enquiries— (pattern data)【PATTERN DATA】

Avg. Recon Cost£3,000–£5,500【PLACEHOLDER — confirm vs cost sheet】

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

M104.944 (S280)1993–1998193 bhp (142 kW) @ 5,500 rpm · 270 Nm @ 3,750 rpm— (pattern data)【PATTERN DATA】£3,000–£5,500【PLACEHOLDER — confirm vs cost sheet】

M104 (S320)1991–1998231 bhp (170 kW) @ 5,600 rpm · 315 Nm @ 3,750 rpm— (pattern data)【PATTERN DATA】£3,200–£6,000【PLACEHOLDER — confirm vs cost sheet】

M112 (S350)2003–2005245 bhp (180 kW) @ 5,700 rpm · 350 Nm @ 3,000 rpm— (pattern data)【PATTERN DATA】£3,500–£6,500【PLACEHOLDER — confirm vs cost sheet】

M113 (S420)1999–2005279 bhp (205 kW) · 400 Nm— (pattern data)【PATTERN DATA】£4,000–£7,500【PLACEHOLDER — confirm vs cost sheet】

Technical Specs

M113 — S420

Displacement3,199 cc

CylindersInline‑6, 24 valves, DOHC

ConstructionCast‑iron block, aluminium head

Fuel SystemMulti‑point fuel injection

Oil Capacity7.5 litres

Displacement3,724 cc (3.7L)

CylindersV6, 18 valves, SOHC

ConstructionAll‑aluminium block and heads

Fuel SystemMulti‑point fuel injection

Transmission5G‑Tronic 5‑speed automatic

Displacement4,196 cc (4.2L)

CylindersV8, 24 valves, SOHC

ConstructionAll‑aluminium block and heads

Fuel SystemMulti‑point fuel injection

Transmission5G‑Tronic 5‑speed automatic

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Market Intelligence

Most Common Failure

M104 head gasket failure (S280/S320) and M113 timing chain tensioner wear (S420) — approximately 60% of S‑Class petrol enquiries cite head gasket, timing or oil leak concerns【PATTERN DATA】

Average Enquiry Mileage

80,000

–150,000 miles【PATTERN DATA】

Average Replacement Cost

£5,000

reconditioned, supply only【PLACEHOLDER】

Most Requested Engine Code

M104 — W140‑era S320 is the most commonly enquired S‑Class petrol【PATTERN DATA】

Peak Enquiry Season

Winter — cold starts expose timing chain and head gasket issues【PATTERN DATA】

Regional Demand

South East22%

London18%

South West (14%)【PATTERN DATA】

Regional Demand Breakdown

22%South East

18%London

Frequently Asked Questions

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