2019 What Car? Reliability Survey: coupés, convertibles and sports cars

To help you choose the most dependable car, we've crunched the data on more than 18,000 vehicles, spanning 31 brands and 218 models to give each a unique reliability rating...

BMW M4 reliability

Coupés, convertibles and sports cars

Average reliability for class 92.9%

Most reliable BMW M4 (2014-present) 99.3%

What went wrong? Bodywork 6%

The BMW M4 is a four-star sports car and a dependable choice, too, with just 6% suffering a fault. The only area of concern was bodywork, and all cars were drivable and repaired under warranty within a day. 

The Mazda MX-5 has long held a reputation for reliability, and the latest model continues that trend. Only 9% had a problem, with non-engine electrical faults the most common at 6%, followed by 4% on the bodywork and 2% on the air-con, battery, brakes and sat-nav. Half of owners’ cars were fixed in a day and no repair bill exceeded £300. 

It may be the cheapest model in the Porsche stable, but the 718 Boxster is one of the best for reliability. Although 38% of cars had a fault, they were relatively minor; interior trim faults were the most common, followed by bodywork, air-con and the exhaust. All could still be driven and most were fixed in a week or less under warranty. 

BMW 4 Series Coupe vs Mercedes C-Class Coupe

Least reliable Mercedes-Benz C-Class Coupé (2016-present) 83.8%

What went wrong? Gearbox/clutch 17% Non-engine electrics 17% Engine 6% Exhaust 6% Interior trim 6% Suspension 6%

Not all Mercedes-Benz C-Class Coupés are a joy to live with; 28% of those we were told about suffered a fault. The biggest issues were with the gearbox/clutch and non-engine electrics. A quarter were out of action for more than a week, and while most work was done under warranty, some of it resulted in bills ranging from £1001 to £1500. 

A quarter of Ford Mustangs played up, with the bodywork and air-con the most common trouble spots. More than half took more than a week to fix; most work was free, but some of it cost up to £500. 

Almost a third of the BMW 6 Series owners in our survey reported faults with their cars' bodywork, brakes, engine, exhaust, interior trim, non-engine electrics and sat-nav. Most could still be driven and were fixed under warranty, but a few cost up to £750 to repair. 

Reliability for coupes, convertibles and sports cars aged up to five years old

Rank Make and model Score
1. BMW M4 2014-on 99.3%
2. Mazda MX-5 2015-on 96.5%
3. 718 Boxster 2016-on 93.9%
4. BMW 2 Series Coupe 2014-on 93.4%
5. BMW 4 Series Coupe 2014-on 93.2%
6. Audi TT 2015-on 92.0%
7. Mini Convertible 2016-on 91.9%
8. BMW 6 Series 2011-2018 89.8%
9. Ford Mustang 2018-on 88.9%
10. Mercedes-Benz C-Class Coupé 2016-on 83.8%

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