MERCEDES 420 (1991)
Running costs, reliability data, and common problems from 44 real MOT tests.
Annual Cost
£2,907
£242/month
MOT Pass Rate
77%
Average
Road Tax
£760
Based on CC/year
Insurance
Grp 35-50
4196cc Petrol
Check Carefully
77% pass rate, £2907/year to run. 5 points below average.
Check a specific MERCEDES 420
Enter a reg plate for full MOT history, mileage check, health score, running costs, and reliability data. Free, instant, no signup.
Annual Running Costs
~30 mpg
Based on 4196cc
Based on 7,400 miles/year (UK average), current fuel prices, and repair likelihood from MOT data. Insurance not included.
Get an insurance quote for this MERCEDES 420
Compare quotes and find the best deal
Reliability Verdict
Average reliability. Expect some repairs as it ages. That's close to the national average of 82%. It falls below the MERCEDES brand average of 87%.
At 35 years old, 77% of MERCEDES 420s from 1991 passed their MOT first time in 2026. That's based on 44 tests across the UK. The average mileage at this age is 131,577 miles.
Got a MERCEDES 420 you're looking at?
Enter the reg plate to check its specific MOT history, mileage, and health score.
How Does It Compare?
Mileage Analysis
131,577
Average miles
259,000
Expected for age
The average 1991 MERCEDES 420 has 131,577 miles on the clock, which is below the expected 259,000 miles for a 35-year-old car. This suggests lighter use than average, which generally means less wear on major components.
Looking at a specific MERCEDES 420?
Enter its reg plate for a free check with full MOT history, mileage verification, and predicted costs.
Similar Cars to Consider
Check a Specific Mercedes 420
Enter a reg plate to get the full MOT history, health score, and mileage verification.
Upgrade to Premium (£4.99) for stolen, finance, and write-off checks.
About the 1991 MERCEDES 420
The 1991 MERCEDES 420 is a performance with a 4196cc petrol engine. 44 of these vehicles were MOT tested in 2026, making it a rare model on UK roads. Among all cars from 1991, the average MOT pass rate is 78%, and this model falls short of that benchmark.
With an average of 131,577 miles at 35 years old, 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 £1,592 per year at current petrol prices of 142p per litre (based on 7,400 miles per year).
What does it cost to own a 1991 MERCEDES 420?
Total estimated annual running cost is £2,907 (£242/month), broken down as £1592 fuel, £760 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
Based on the 1991 MERCEDES 420's fuel type, age, and engine size, these are the most likely problem areas to check.
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 annual running costs, insurance, and tax.
| Car | Pass Rate | Fuel/yr | Tax/yr | Insurance | Total/yr |
|---|---|---|---|---|---|
| MERCEDES 420(1991) | 77% | £1592 | £760 | Grp 35-50 | £2907 |
| LAND ROVER RANGE ROVER(1993) | 81% | £1592 | £250 | Grp 35-50 | £2247-£660 |
| JAGUAR XJS(1993) | 84% | £1592 | £250 | Grp 35-50 | £2247-£660 |
| TVR GRIFFITH(1992) | 88% | £1592 | £250 | Grp 35-50 | £2247-£660 |
| TVR CHIMAERA(1993) | 84% | £1592 | £250 | Grp 35-50 | £2247-£660 |
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
LAND ROVER RANGE ROVER
1993 · 3950cc Petrol
JAGUAR XJS
1993 · 3980cc Petrol
TVR GRIFFITH
1992 · 3948cc Petrol
Related Guides
In-depth articles relevant to the Mercedes 420.
Cars That Lose Value Fastest: Models to Avoid for Depreciation
8 min read
Running CostsCheapest Cars to Run in 2026: Real Data from 19.8 Million MOT Tests
9 min read
Running CostsCheapest Cars to Insure in the UK: Insurance Groups 1-10
9 min read
Buying GuideFord Fiesta Common Problems (2026): What to Check Before Buying
13 min read
ReliabilityFord Puma Problems: 7 Issues Owners Report (2026)
13 min read
Check a specific MERCEDES 420
Enter the reg to see its MOT history, mileage check, and predicted costs.
Premium History Check
Buying a MERCEDES 420? Our premium check covers:
- Stolen check (PNC)
- Outstanding finance
- Write-off history (Cat A/B/N/S)
- Previous owners count
Competitors charge £10-£20 for the same data