MERCEDES S 350 L AMG LINE PREMIUM + D A (2021)
Running costs, reliability data, and common problems from 161 real MOT tests.
Annual Cost
£1,695
£141/month
MOT Pass Rate
96%
Excellent
Road Tax
£195
Flat rate/year
Insurance
Grp 30-42
2925cc Diesel
Great Choice
96% pass rate, £1695/year to run. 14 points above average.
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Annual Running Costs
~40 mpg
Flat rate (post-2017)
Low estimate due to excellent reliability
Based on 7,400 miles/year (UK average), current fuel prices, and repair likelihood from MOT data. Insurance not included.
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Reliability Verdict
Excellent reliability. Very few MOT failures. That's 14 points above the national average of 82%. It also outperforms the MERCEDES brand average of 87%.
At 5 years old, 96% of MERCEDES S 350 L AMG LINE PREMIUM + D As from 2021 passed their MOT first time in 2026. That's based on 161 tests across the UK. The average mileage at this age is 35,442 miles.
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How Does It Compare?
Mileage Analysis
35,442
Average miles
37,000
Expected for age
The average 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A has 35,442 miles on the clock, which is in line with the expected 37,000 miles for a 5-year-old car, suggesting normal everyday use.
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About the 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A
The 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A is a large car with a 2925cc diesel engine. 161 of these vehicles were MOT tested in 2026, making it a rare model on UK roads. It ranks in the top 3% of all 2021 cars for reliability.
With an average of 35,442 miles at 5 years old, MERCEDES S 350 L AMG LINE PREMIUM + D A owners drive about as much as the UK average.
2021 MERCEDES S 350 L AMG LINE PREMIUM + D A Fuel Costs
The 2925cc diesel engine is on the larger side, so fuel won't be this car's strong point. Expect around 40 mpg in mixed driving, which works out to roughly £1,245 per year at current diesel prices of 148p per litre (based on 7,400 miles per year). Diesel cars of this age should have their DPF (diesel particulate filter) checked, as replacements can be costly.
What does it cost to own a 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A?
Total estimated annual running cost is £1,695 (£141/month), broken down as £1245 fuel, £195 road tax, £55 MOT, and £200 predicted repairs. The low repair estimate reflects the excellent 96% pass rate. These cars rarely fail their MOT, so unexpected bills are less likely.
Buying a Used 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A
At 5 years old, the MERCEDES S 350 L AMG LINE PREMIUM + D A offers good value with plenty of life remaining. Most manufacturer warranties will have expired, so a pre-purchase inspection is worth the cost.
Common Issues to Watch For
Based on the 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A's fuel type, age, and engine size, these are the most likely problem areas to check.
DPF (Diesel Particulate Filter)
Watch outShort journeys clog the DPF. Replacement costs £1,000-£2,500. Check the DPF warning light and ask about driving patterns.
Turbo Wear
Medium riskDiesel turbos work harder and wear faster. Listen for whining noises and check for oil leaks around the turbo housing.
AdBlue System
Medium riskPost-2015 diesels use AdBlue for emissions. Sensor failures and tank heater issues are common. Budget £200-£500 for repairs.
EGR Valve
Low riskExhaust Gas Recirculation valves clog with carbon deposits, causing rough running and poor economy. Cleaning costs £150-£300, replacement £300-£600.
Dual Mass Flywheel
Medium riskLarger diesel engines put extra strain on the dual mass flywheel. Listen for rattling at idle. Replacement with clutch is £800-£1,500.
Service History
Low riskAlways request a full service history. Regular servicing is the single best indicator of how well a car has been maintained, regardless of mileage.
Running Costs Compared
How the 2021 MERCEDES S 350 L AMG LINE PREMIUM + D A stacks up against similar cars for annual running costs, insurance, and tax.
| Car | Pass Rate | Fuel/yr | Tax/yr | Insurance | Total/yr |
|---|---|---|---|---|---|
| MERCEDES S 350 L AMG LINE PREMIUM + D A(2021) | 96% | £1245 | £195 | Grp 30-42 | £1695 |
| MERCEDES E(2019) | 90% | £1245 | £190 | Grp 30-42 | £1690-£5 |
| FORD RANGER(2019) | 87% | £1245 | £190 | Grp 35-50 | £1840+£145 |
| AUDI Q5(2019) | 93% | £1245 | £190 | Grp 30-42 | £1690-£5 |
| AUDI A5(2019) | 90% | £1245 | £190 | Grp 30-42 | £1690-£5 |
Estimates based on 7,400 miles/year, current fuel prices, and MOT data. Insurance groups are indicative. Actual costs vary by driver, location, and usage.
Related Mercedes Models
Explore other Mercedes cars or similar models in the same category.
MERCEDES A
2019 · 1461cc Diesel
MERCEDES C
2017 · 1991cc Hybrid
MERCEDES A-CLASS
2017 · 1461cc Diesel
MERCEDES E
2019 · 2925cc Diesel
FORD RANGER
2019 · 3198cc Diesel
AUDI Q5
2019 · 2967cc Diesel
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