Mercedes Benz SL 280/350 Petrol Engine ReplacementCompare Prices & Get Quotes
Get quotes today from trusted UK Mercedes Benz SL 280 and 350 petrol engine specialists. Compare prices on reconditioned, rebuilt and used engines for the 2.8-litre inline-six and the 3.5-litre V6 - supply & fit available nationwide.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £1,600 to £4,500
Used from £1,200 · Reconditioned from £1,600 · Common codes: M104.943, M112.923, M272.967, M276.952
From £1,200
Tested, bare/short engine
From £1,600
Rod bearings addressed, tested
From quote
Upgraded bearings, full teardown, revised valvetrain
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3 Simple Steps3 Simple Stepsto Finding the Best Mercedes Benz SL 280/350 Petrol Replacement Engineto Finding the Best Mercedes Benz SL 280/350 Petrol Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryMercedes Benz SL 280/350 Petrol - Engine History & Specs at a Glance
The SL 280 and SL 350 have represented the entry-level and mid-range petrol options across three generations of Mercedes' iconic roadster. The SL 280 debuted in the R129 generation in 1992 with the M104 2.8-litre inline-six, offering 193hp of smooth, refined power. The SL 350 arrived with the R230 generation in 2001, powered by the M112 3.7-litre V6 producing 245hp - later replaced by the M272 3.5-litre V6 in 2004 with 268hp, and finally the M276 3.5-litre V6 in the R231 generation with 306hp. These engines represent the accessible yet refined heart of the SL range.
Variant HistoryMercedes Benz SL 280/350 Petrol - Engine History & Specs at a Glance
The SL 280 and SL 350 have represented the entry-level and mid-range petrol options across three generations of Mercedes' iconic roadster. The SL 280 debuted in the R129 generation in 1992 with the M104 2.8-litre inline-six, offering 193hp of smooth, refined power. The SL 350 arrived with the R230 generation in 2001, powered by the M112 3.7-litre V6 producing 245hp - later replaced by the M272 3.5-litre V6 in 2004 with 268hp, and finally the M276 3.5-litre V6 in the R231 generation with 306hp. These engines represent the accessible yet refined heart of the SL range.
Mercedes Benz SL 280/350 Petrol
Fuel TypePetrol (naturally aspirated inline-six and V6; later biturbo V6)
Engine Size Range2.8L-3.7L (M104: 2,799cc; M112: 3,724cc; M272: 3,498cc; M276: 3,498cc)
Power Output Range193-306hp across the variant's historyEngine History Timeline
M104.943 2.8L inline-six, 193hp @ 5,500rpm (SL 280, R129)
M112.923 3.7L V6, 245hp @ 5,750rpm (SL 350, R230 launch)
M272.967 3.5L V6, 268hp @ 6,000rpm (SL 350, R230 facelift)
M276.952 3.5L V6, 306hp @ 6,500rpm (SL 350, R231 launch)
M276.952 3.0L V6 biturbo, 333hp (SL 400, R231, effectively replaces SL 350)
Key Specs Snapshot
Fuel TypePetrol (naturally aspirated inline-six and V6; later biturbo V6)Engine Size Range2.8L-3.7L (M104: 2,799cc; M112: 3,724cc; M272: 3,498cc; M276: 3,498cc)Power Output Range193-306hp across the variant's historyYears Produced1992-2014Every engine fitted to the Mercedes Benz SL 280 and 350 petrol is covered below, with UK rebuilt pricing and known failure points - from M104 biodegradable wiring harness failure to M272 balance shaft wear and M276 timing chain tensioner issues.
Mercedes Benz SL 280/350 Petrol Engine Codes - Specifications & Replacement CostMercedes Benz SL 280/350 Petrol Engine Codes - Specifications & Replacement Cost
2.8L Inline-Six Petrol (1992-1997)
Power Output193 hp (142 kW) @ 5,500 rpmTorque270 Nm @ 3,750 rpmYears Fitted1992-1997Displacement2,799 ccCylindersInline 6, DOHC, 24-valveEngine CodeM 104 E 28 / 104.943
Compatible Trim Levels
- SL 280
- SL 280 Sport
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£1,200-£1,800
Reconditioned
Addressed known issues, tested
£1,800-£2,500
Rebuilt
Full teardown, upgraded internals
£2,200-£3,200
Common Failure
Biodegradable wiring harness degradation - M104 engines in 1993-1995 models suffer from wiring harness insulation breaking down, causing electrical faults, misfires and rough running. Timing chain tensioner wear and vacuum leaks from intake manifold gaskets are also common on higher-mileage examples.
The SL 280's M104 inline-six and the SL 350's M112, M272 and M276 V6s are among Mercedes' most refined petrol engines, but each has well-documented weaknesses that become more pronounced with age and mileage. The M104 is notorious for biodegradable wiring harness failure, while the M272 suffers from balance shaft idler gear wear. Every rebuilt engine supplied through EnginesMarket includes upgraded components addressing these original failure points, plus a minimum 12-month unlimited-mileage warranty.
The Classic SL 280's Electrical Nemesis
Affected Vehicles
Mercedes SL 280 (M104.943, 1993-1995)
Typical Failure Mileage
70,000-100,000 miles
Root Cause
Mercedes used a biodegradable insulation material on wiring harnesses from 1993-1995. Over time, the insulation breaks down, causing short circuits, misfires, rough running and, in severe cases, no-start conditions. This is the single most common electrical issue on early R129 SL models. One owner reported replacing the wiring harness on their 1994 280SL to resolve persistent running issues.
Why It Happens
Mercedes used a biodegradable insulation material on wiring harnesses from 1993-1995. Over time, the insulation breaks down, causing short circuits, misfires, rough running and, in severe cases, no-start conditions. This is the single most common electrical issue on early R129 SL models. One owner reported replacing the wiring harness on their 1994 280SL to resolve persistent running issues.
Dealer (parts + labour)
£150-£300
Specialist (parts + labour)
£100-£200
What it involves
Visual inspection of engine wiring harness, especially injector and sensor circuits
Suitability
First step - confirms whether harness is the cause
1 - 2 daysDealer (parts + labour)
£1,500-£2,500
Specialist (parts + labour)
£900-£1,500
What it involves
Replace complete engine wiring harness with updated non-biodegradable unit
Suitability
If harness degradation is confirmed
1 - 2 daysDealer (parts + labour)
£4,000-£5,500
Specialist (parts + labour)
£2,200-£3,200
What it involves
Complete engine swap with new wiring harness and seals, 12-month warranty
Suitability
If electrical faults have caused engine damage
1 - 2 daysAll prices are indicative UK market ranges based on current UK specialist supplier data.| Repair Tier | Dealer (Parts + Labour) | Specialist (Parts + Labour) | What It Involves | Suitability | Estimated Time |
|---|---|---|---|---|---|
 Diagnostics - Wiring harness inspection Minor | £150-£300 | £100-£200 | Visual inspection of engine wiring harness, especially injector and sensor circuits | First step - confirms whether harness is the cause | 1 - 2 days |
 Intermediate - Engine wiring harness replacement Best Value | £1,500-£2,500 | £900-£1,500 | Replace complete engine wiring harness with updated non-biodegradable unit | If harness degradation is confirmed | 1 - 2 days |
Full Replacement - Rebuilt M104 engine Best Value | £4,000-£5,500 | £2,200-£3,200 | Complete engine swap with new wiring harness and seals, 12-month warranty | If electrical faults have caused engine damage | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
A typical 1992-1997 SL 280 is worth approximately £5,000-£15,000 depending on condition and mileage. These classic roadsters are appreciating assets for well-maintained examples, making engine replacement a justifiable investment for preservation-minded owners.
Our Recommendation
Our Recommendation
If your SL 280 experiences intermittent running issues, misfires or warning lights, have the wiring harness inspected immediately. Replacing the biodegradable harness with an updated unit at a specialist is significantly cheaper than dealer rates. On an SL 280 worth £5,000-£15,000, this is a worthwhile investment to preserve the vehicle's value and reliability.
Don't Let Wiring Harness Failure, Balance Shaft Wear, or Timing Chain Rattle Write Off Your Mercedes SL 280 or 350 Petrol
Whether you're facing M104 wiring harness degradation on your classic SL 280, M272 balance shaft wear on your R230 SL 350, or M276 timing chain rattle on your R231, EnginesMarket makes it simple to compare quotes from trusted UK Mercedes petrol specialists. Every rebuilt engine in our network carries upgraded components addressing the original design weakness - new wiring harnesses, hardened balance shaft gears, and updated tensioners - plus a minimum 12-month unlimited mileage warranty with nationwide delivery and supply & fit options. Don't pay main dealer premiums. Compare prices from independent Mercedes specialists who know these classic and modern SL petrol engines inside out.
Compare rebuilt M104 Mercedes SL 280 engine prices
12-Month Minimum
UK Specialists Vetted
Best Price GuidanceImportant Information
Important Information
"All prices are indicative UK market ranges based on historical quote data and repair requests from our network of engine specialists. Dealer pricing is estimated based on published main dealer labour rates and genuine OEM parts pricing. Specialist pricing reflects actual quote data from EnginesMarket's UK network. Actual costs vary depending on damage severity, vehicle condition, variant, and workshop location within the UK. Use our free comparison tool to get tailored quotes for your specific Mercedes SL 280 or 350 petrol. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty - always confirm exact terms with your chosen supplier."
Mercedes Benz SL 280/350 Petrol Engine ReplacementFrequently Asked Questions
Question 1How much does a Mercedes SL 280 or SL 350 petrol engine replacement cost in the UK-
Short summary: A rebuilt M104 engine for the SL 280 costs £2,200-£3,200 supply-only; a rebuilt M272 engine for the SL 350 costs £2,800-£4,500 supply-only. Fitting adds £800-£1,500 depending on complexity - V6 work requires specialist knowledge.
- SL 280 (M104.943): rebuilt unit £2,200-£3,200; used engine from £1,200
- SL 350 (M112.923): rebuilt unit £2,500-£3,800; used engine from £1,400
- SL 350 (M272.967): rebuilt unit £2,800-£4,500; used engine from £1,500
- SL 350 (M276.952): rebuilt unit £3,200-£4,500; used engine from £1,800
- M272 balance shaft replacement: £2,400-£3,600 at specialist
Question 2What are the signs of M272 balance shaft failure on a Mercedes SL 350-
Short summary: A rattling noise on cold start lasting a few seconds is the classic warning sign on the M272 V6 engine. If ignored, it can lead to catastrophic engine failure. M272 engines with engine numbers below 2729..30 468933 require updated balance shaft parts per Mercedes TSB.
- Cold start rattle that disappears after oil pressure builds - earliest warning
- Check engine light with timing correlation codes (P0016, P0017)
- Metallic swarf in engine oil indicates balance shaft gear wear
- If caught early, balance shaft replacement costs £2,400-£3,600 at specialist
Question 3Is the Mercedes SL 280 or SL 350 petrol engine reliable-
Short summary: The M104, M112, M272 and M276 engines are all fundamentally refined and durable, but each has well-documented weaknesses. The M104's biodegradable wiring harness affects 1993-1995 models, while the M272's balance shaft wear is a known catastrophic failure. With these addressed, all are capable of 150,000+ miles.
- M104 inline-six is smooth but wiring harness vulnerability is critical
- M112 V6 is robust but harmonic balancer failure is age-related
- M272 V6 balance shaft wear is the most critical failure point
- M276 V6 timing chain tensioner wear affects cold starts
- Regular oil changes with MB 229.5 spec oil are essential
Question 4How long do Mercedes SL 280 and SL 350 petrol engines last-
Short summary: Properly maintained M104, M112, M272 and M276 engines routinely reach 150,000-200,000 miles before major work. Balance shaft issues on the M272 typically appear between 60,000-90,000 miles.
- M104 (SL 280): 150,000-200,000 miles with regular servicing
- M112 (early SL 350): 150,000-200,000 miles with proper maintenance
- M272 (SL 350): 150,000-200,000 miles - balance shaft inspection from 60k miles
- M276 (SL 350): too early for definitive data - tensioner issues from 60k miles
Question 5Is it worth replacing the engine in my Mercedes SL 280 or SL 350 petrol-
Short summary: Yes, if the SL is otherwise in good condition with no rust or major transmission faults. A rebuilt M104 costs £2,200-£3,200 - far less than replacing a £5,000-£15,000 classic. The SL 350's higher value (£6,000-£30,000) makes replacement even more justifiable.
- SL 280 values: £5,000-£15,000 depending on condition
- SL 350 values: £6,000-£30,000 - strong values for well-maintained examples
- Rebuilt engine with upgraded components fixes original weak points
- Supply & fit typically £3,000-£6,000 depending on engine code
- New engine includes 12-month unlimited mileage warranty
Question 6What oil does my Mercedes SL 280 or SL 350 petrol need-
Short summary: Mercedes-Benz specifies MB 229.5 high-performance oil - typically 5W-30 or 5W-40 fully synthetic. The M104 requires approximately 6.5 litres; the M112/M272/M276 V6s require approximately 7.5-8.0 litres.
- M104 (SL 280): MB 229.5 5W-30 or 5W-40 - 6.5L capacity
- M112/M272/M276 (SL 350): MB 229.5 5W-30 or 5W-40 - 7.5-8.0L capacity
- Never use non-approved oil - can cause timing chain and hydraulic lifter issues
- Change every 10,000 miles or 12 months
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supply & fit available for M104, M112, M272 and M276
Comparing quotes for your Mercedes SL 280 or SL 350 petrol is completely free, with no obligation and no pressure. Enter your registration above to get tailored quotes from UK Mercedes petrol specialists who understand the M104, M112, M272 and M276 engines inside out. Whether you need a used engine, a reconditioned unit, or a full rebuilt engine with upgraded wiring harnesses, balance shaft gears, timing components and seals, we'll connect you with the right specialist for your exact SL - with a minimum 12-month warranty on every engine supplied.
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