Mercedes 420 (1991)
Estimated running costs and MOT pass rates from 44 MOT tests in 2024.
Annual Cost
£2,888
£241/month
MOT Pass Rate
77%
Average
Road Tax
£375
Estimated/year
Est. Insurance
Grp 35-50
4196cc Petrol
Check Carefully
77% pass rate, £2,888/year to run. 5 points below average.
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Annual Running Costs
~30 mpg
Pre-2001 engine size rate
Estimates based on 7,400 miles/year (UK average), petrol at 174.57p a litre (GOV.UK weekly average, week of 19 October 2026), GOV.UK road tax rates and repair likelihood from MOT data. Insurance not included.
Reliability Verdict
Average reliability. Expect some repairs as it ages. That's close to the average of 82% across all models in our data. It falls below the Mercedes brand average of 87%.
77% of MOT tests on Mercedes 420s from 1991 ended in a pass in 2024, when they were about 33 years old. That's based on 44 tests across the UK, retests included. The average mileage recorded at those tests was 131,577 miles.
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How Does It Compare?
Mileage Analysis
131,577
Average miles
244,200
Expected for age
The average 1991 Mercedes 420 had 131,577 miles on the clock at its 2024 MOT, which is below the expected 244,200 miles for a 33-year-old car. This suggests lighter use than average, which generally means less wear on major components.
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About the 1991 Mercedes 420
The 1991 Mercedes 420 is a premium performance car. Our records list a 4196cc petrol engine, though engines vary between versions. 44 MOT tests were recorded on this model in 2024, making it a rare model on UK roads. Among all models from 1991, the average MOT pass rate is 79%, and this model falls short of that benchmark.
With an average of 131,577 miles recorded at its 2024 MOT tests, Mercedes 420 owners tend to use this car less than the typical driver.
1991 Mercedes 420 Fuel Costs
The 4196cc petrol engine is on the larger side, so fuel won't be this car's strong point. Expect around 30 mpg in mixed driving, which works out to roughly £1,958 per year with petrol at 174.57p per litre (GOV.UK weekly average, week of 19 October 2026; based on 7,400 miles per year).
What does it cost to own a 1991 Mercedes 420?
Total estimated annual running cost is £2,888 (£241/month), broken down as £1,958 fuel, £375 road tax, £55 MOT, and £500 predicted repairs. Repair costs are moderate, reflecting the 77% pass rate. Keeping on top of servicing will help avoid surprises.
Buying a Used 1991 Mercedes 420
At 35 years old, the Mercedes 420 is firmly in budget territory. Purchase prices are low, but check for rust, worn suspension bushes, and electrical gremlins. A full service history is especially valuable at this age. Note: with only 44 tests in our data, these figures should be treated as indicative rather than definitive.
Common Issues to Watch For
These are typical issues for cars of this age, fuel type and engine size, not faults recorded on this model's MOT tests. Use them as a checklist when you view one.
Timing Chain / Belt
Watch outAt 35 years old, check whether the timing belt has been replaced (typically due every 5-7 years or 60,000-100,000 miles). A snapped belt can destroy the engine.
Oil Consumption
Medium riskLarger petrol engines can develop higher oil consumption as they age. Check the oil level and look for blue smoke from the exhaust.
Rust and Corrosion
Watch outAt 10+ years, check wheel arches, sills, subframe, and brake lines for rust. Structural corrosion is an MOT failure. Prevention is far cheaper than repair.
Suspension Bushings
Watch outRubber suspension bushes harden and crack with age, causing knocking noises and vague handling. A full refresh costs £300-£800 depending on the car.
Clutch Wear
Watch outWith an average of 132k miles, clutch replacement may be due (typical lifespan 60,000-100,000 miles). Budget £400-£800 for a new clutch kit.
Brake Discs and Pads
Medium riskHigh-mileage cars often need brake disc replacement, not just pads. A full set of discs and pads costs £200-£500 per axle.
Engine Mounts
Medium riskWorn engine mounts cause excessive vibration and movement. Replacement costs £150-£400 per mount. Check for vibration at idle with the bonnet open.
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 1991 Mercedes 420 stacks up against similar cars for estimated annual running costs, insurance group, and tax.
| Car | Pass Rate | Fuel/yr | Tax/yr | Est. Ins. Group | Total/yr |
|---|---|---|---|---|---|
| Mercedes 420(1991) | 77% | £1,958 | £375 | Grp 35-50 | £2,888 |
| Land Rover Range Rover(1993) | 81% | £1,958 | £375 | Grp 35-50 | £2,738-£150 |
| Jaguar XJS(1993) | 84% | £1,958 | £375 | Grp 35-50 | £2,738-£150 |
| TVR Griffith(1992) | 88% | £1,958 | £375 | Grp 35-50 | £2,738-£150 |
| TVR Chimaera(1993) | 84% | £1,958 | £375 | Grp 35-50 | £2,738-£150 |
Estimates based on 7,400 miles/year, GOV.UK average pump prices for the week of 19 October 2026, GOV.UK road tax rates and MOT data. Insurance groups are our rough estimate from engine size, not official groups. Actual costs vary by driver, location, and usage.
Questions about the 1991 Mercedes 420
Is the 1991 Mercedes 420 reliable?
Average reliability. Expect some repairs as it ages. 77% of MOT tests on 1991 Mercedes 420s ended in a pass, from 44 tests (DVSA MOT data for tests in 2024, retests included). That's 5 points below the average of 82% across all models in the same data.
How much does a 1991 Mercedes 420 cost to run?
Our estimate is £2,888 a year (£241 a month): £1,958 fuel, £375 road tax, £55 MOT and £500 predicted repairs, based on 7,400 miles a year. Insurance is not included.
What is the MOT pass rate for a 1991 Mercedes 420?
77% of 44 MOT tests on the 1991 Mercedes 420 ended in a pass (DVSA MOT data for tests in 2024, retests included). That ranks it 112th of 172 models first registered in 1991 (bottom half).
What is the average mileage for a 1991 Mercedes 420?
The average mileage recorded at MOT tests on the 1991 Mercedes 420 is 131,577 miles, which is below the expected 244,200 miles for a 33-year-old car. This suggests lighter use than average, which generally means less wear on major components.
Related Mercedes Models
Explore other Mercedes cars or similar models in the same category.
Mercedes A
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Mercedes C
2017 · 1991cc Hybrid
Mercedes A-Class
2017 · 1461cc Diesel
Land Rover Range Rover
1993 · 3950cc Petrol
Jaguar XJS
1993 · 3980cc Petrol
TVR Griffith
1992 · 3948cc Petrol
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