Used Mercedes-Benz SLK review and buying guide (1996 to 2016): which one to buy and what to check

Which used Mercedes-Benz SLK should you buy?

The R172 (2011 to 2015) is the SLK to buy, as its two own known faults leave visible signs rather than wrecking an engine. On 2011 to 2013 cars the colour-coded panels flanking the glass roof can peel apart between 30,000 and 80,000 miles and let water into the cabin, and Mars Red and Fire Opal Red paint can blister from as early as 10,000 miles. Its 1.8 (M271) shares the timing chain fault up to 2013; otherwise little's on record about its engines.

The 2004 to 2011 car sits in the middle, and it's the engine that decides whether one's worth having. The 1.8 Kompressor's timing chain stretches and jumps teeth between 60,000 and 90,000 miles, and on 2004 to 2008 cars the sprocket driving the balance shaft in the V6 (SLK 280, 300 and 350) wears away over the same mileage and wrecks the timing. Don't buy any of them without receipts for the timing work, a quiet cold start and no warning light on.

The original R170 (1996 to 2004) is the riskiest of the three. Its folding hardtop and window mechanism can fail between 60,000 and 100,000 miles, often through a sensor or the hydraulic pump, and on a car this old the repair can cost more than the car's worth. Rust in the wheel arches, around the door handles and on the boot lid is a known fault too, so only take one with a roof that works every time and solid metal.

Which SLK engines and gearboxes are the safe choices?

The 1.8 Kompressor (M271) and the 2004 to 2008 V6 (M272) in the SLK 280, 300 and 350 are the engines to be most careful with, as both have serious known faults that destroy the engine's timing. On 2002 to 2013 cars the 1.8's single-row chain stretches and jumps teeth, wrecking the valves, and it's often replaced between 60,000 and 90,000 miles. A metallic rattle for 3 to 5 seconds on a cold start is the warning, so hear it start from cold and ask for the chain receipt.

On the V6, the soft sprocket driving the balance shaft wears away between 60,000 and 90,000 miles on 2004 to 2008 cars, until the cam timing wanders and the engine's wrecked. An engine management light, rough running or a misfire points to it. The fault's recorded years end in 2008, but that isn't proof a later car escapes it, so ask for evidence the sprocket's been looked at on any 2004 to 2011 SLK 280, 300 or 350. The SLK 55 AMG's V8 (M113) isn't the engine this fault names.

On the R170, the SLK320 V6 wears out its right-side pre-catalytic converters and main catalytic converters between 80,000 and 120,000 miles, showing as lost performance, a warning light or a rattle from the exhaust. The 2.3 Kompressor (230K) can let oil seep past the cam magnet and along into the wiring harness, damaging it, and late 230Ks got an extra oil seal to stop that happening.

The R170's auto has had problems, and its fluid and filter want changing every 40,000 miles; the 7G-Tronic in later cars wants the same every 40,000 miles or 48 months to head off conductor plate failure, so ask for the invoices. On R170 manuals, the support on the clutch pedal box fails through fatigue, and the R170's manual gearbox has had isolated failures.

What should you check when viewing a used SLK?

Put the roof through a full cycle at least twice and watch the side windows drop and rise with it. A roof that stalls, jams or groans points to a sensor or the hydraulic pump, and one owner's roof failed twice, first through a micro switch in the boot and then the tubular frame. R170 roof sensors give trouble when the roof isn't used often, so ask how regularly it's been opened.

Lift the carpets and press the seats for damp. Water gets in through delaminated roof panels on 2011 to 2013 cars, one owner had rain getting past the seals around the roof and boot lid, and on a 2008 car blocked bulkhead drains let rainwater flood the heater motor. Check the R170's wheel arches, door handles and boot lid for rust, and get under the back of a 2004 to 2011 car, as one owner's rear subframe had rusted through.

Look along a red 2011 to 2015 car's paint in daylight, on a cold day if you can, because the blistering on Mars Red and Fire Opal Red is worse when it's cold and fades when the car's warm. It looks like tiny raindrops or dots of sap under the lacquer, and peeling lacquer on the bumper valances is part of the same fault. One owner's bare-metal respray blistered again, so a respray doesn't mean it's sorted.

On the test drive, a car on 19-inch wheels will ride hard, and the shocks through them can confuse the airbag system's triggers. Listen for grinding from the rear diff, as one owner found metal in the oil at 40,000 miles, and on a manual make sure the gear linkage feels tight. Ask for receipts for gearbox fluid changes, any timing chain or balance shaft work, and the R172's passenger airbag recall.

Paste the advert into the free check and it runs these against the listing, the MOT history and the DVLA record before you travel.

Is a used Mercedes-Benz SLK R170 (1996 to 2004) worth buying?

Only buy an R170 with a roof that works perfectly and solid metal underneath, because both are known faults and a failed roof on a car this age can cost more to fix than the car's worth. The hardtop and window mechanism can give up between 60,000 and 100,000 miles, and rust bubbles appear on the wheel arches, around the door handles and along the boot lid edges from 70,000 to 120,000 miles.

Original UK cars were 2.3 Kompressor automatics, and that auto will change gear mid-corner when you don't want it to. Sudden downchanges followed by rough running can be a failing mass airflow sensor rather than the gearbox itself. The steering's an old recirculating ball set-up and the driving position's offset, so drive one properly before you decide it suits you. It scored four stars in the 2002 crash tests.

Manual cars need the clutch pedal box checking, because its support fails through fatigue. One owner points out the clutch slave cylinder sits inside the bellhousing, which makes replacing it a labour-heavy job, and brake fluid changes don't always bleed it. Indicators that work only some of the time can come down to a relay in the control module, which can be soldered in rather than replacing the whole unit.

On a six-cylinder car, ask whether the worldwide recall to check and, where needed, replace the alternator's voltage regulator on 2001 to 2004 petrols has been done. Foglamps let moisture in and mist up, so look inside the lenses too. The SLK320's pre-catalytic and main catalytic converters are a known weak spot between 80,000 and 120,000 miles, so listen for an exhaust rattle.

Should you buy a Mercedes-Benz SLK R172 (2011 to 2015)?

Yes, the R172 is the one to go for, as long as it's dry inside and the paint's clean. On 2011 to 2013 cars the colour-coded panels flanking the glass roof come apart between 30,000 and 80,000 miles, bowing upwards in hot weather and letting water run through the roof's workings onto the seats and carpets. One owner of a 2012 SLK 250 CDI saw the back of the roof lift in sunshine, and the fault's years ending in 2013 doesn't make a later car safe.

The paint's the other known fault. Mars Red and Fire Opal Red cars from 2011 to 2015 get micro-blistering and peeling lacquer between 10,000 and 50,000 miles, with six owner reports behind it. The fix is often a full respray back to bare metal, and one owner's blisters came back after that, bigger this time, across the bonnet, front wings, front bumper, driver's door and a rear wing. Any red R172 needs a slow walk round.

On a 2011 to 2013 car with the 1.8 (M271), the High timing chain fault applies, so hear it start from cold; otherwise there's little on record about the R172's engines. One owner's 2013 SLK350 had its RPM and NOx sensors, heater box and aerial replaced by 19,700 miles, and another owner's driver's door lock jammed. A recall covered the passenger airbag on SLKs from 2011, so ask for proof it's been done.

What does a used Mercedes-Benz SLK cost to run?

What do SLK owners like about them?

The R172 makes a proper grand tourer. It rides comfortably and has a laid-back, unhurried manner, so it's happy covering long trips and doesn't need to be driven hard to be enjoyed. That easy-going nature is what the car's built around, and it suits a buyer who wants to cruise with the roof down.

There's a broad choice of engines in the R172, a diesel among them, and every one of them can be paired with the seven-speed automatic, so you aren't pushed into one engine just to get a self-shifting gearbox. The 2004 to 2011 car is more of a sports car at heart, for someone who wants a two-seater with a sharper focus.

• This model received a strong four-star rating for occupant protection in 2002 NCAP assessments.
• Mercedes recorded the fifth lowest average expenditure on warranty claims for cars up to ten years old in 2002.
• The model generally had the ninth lowest average warranty repair costs in the 2003 Warranty Direct Reliability index.
• Fewest problems and faults were reported, with an average number of breakdowns in a 2003 Which survey.
• This model earned a four-star crash safety rating in 2002 NCAP tests, with low warranty claim expenses.