- Available for £12,000
- 6.2 V8, normally aspirated, rear-wheel drive
- M156 motor is epic across a huge rev range
- Mech issues should have all been sorted on remaining cars
- CLK coupe is elegant, Cabrio hoods can be troublesome
- Black Series version is excellent but pricey
Some cars are revered for their looks, others for their quality, heritage, luxury, power or performance. Very rarely, a car will manage to hit every target you can think of. Such cars are invariably beyond the means of most of us, but the good news is that even those of us on a conventional income can enjoy prime motoring as long as we're prepared to be happy with one or two areas of individual excellence. In bingo terms, aiming for a line rather than a full house.
If the area you choose is headed 'great engine', Mercedes' M156 V8 should do the job. Making its debut in the 2006 E63 AMG, the 6.2 was then lobbed into the ML63 AMG, R63 AMG and S63 AMG before it was found under the bonnet of the 2007MY-on C209/A209 CLK 63 that is the subject of this buying guide. It was the first engine that AMG built for Mercedes; Porsche Carrera GT engine architect Bernd Ramler helmed the M156 project, and AMG had plenty of beefy heritage of its own, so you can imagine the pride and missionary zeal that went into getting it right.
The frameless-windowed CLK coupe offered understated elegance in all its variations. In CLK63 form it added the M156's hammering power to the brew. Although the M156's actual displacement was 6,208cc, it was marketed as a 6.3 as a respectful nod to M-B's first V8, the dry-sump 6,332cc SOHC unit that powered the iconic 600 limo of the early '60s and, later on, the titanic W109 300 SEL 6.3. Featuring aluminium alloy heads, forged rods, pistons and crank and sodium-filled valves, the M100 was a handbuilt masterpiece. Each one was bench-tested for nearly four and a half hours, three quarters of an hour of that being under full load.
The M156 picked up that bombastic M100 baton and went from there. Despite its cavernous displacement, the new motor revved harder than most inline fours a third its size. If you thought the CLK 63's peak torque was a bit late arriving at 5,000rpm, that was nothing: there was another 1,800rpm to go beyond that before it hit peak power. The rev limiter didn't cut in until 7,200rpm. In a 6.2 litre engine. Think about that for a second.
It all looks a bit mad against the low-rpm turbo motors of today which routinely deliver the 'heads you lose, tails I win' combo of more power, more low-end overtaking punch and more miles per gallon, but those modern motors don't deliver as much drama as the M156. The fact that it could run at such high engine speeds while maintaining a good reliability record is a tribute to the strength and integrity of the design. Well, we say good reliability, but it was far from perfect in the early days. We'll get into that in the Powertrain section.
Although the 622hp M159 in 2012's SLS Black Series took the record for the most powerful normally aspirated production V8, the CLK 63 wasn't short of heft at 475hp. Its fuel consumption was noteworthy for all the wrong reasons: the official combined figure was below 20mpg, M-B confessed to 13mpg in urban use, and single-figure readings were well within reach among owners who liked leaning on the loud pedal - but it was hard to find a meatier sounding car. Plus it was used as F1's official safety car for the first two years of its life, so it had good street cred.
You could get it as a Cabriolet too. Nerd fact: Mercedes-Benz reckoned that you were just as safe from lightning in a CLK Cabriolet as you were in a coupe, or any car with a metal roof, thanks to the electricity-friendly cage made up by the soft-top frame assembly's struts and crossmembers - although we're not sure if the 'field-free zone' was a deliberate or accidental result of the design.
In 2007 Mercedes launched the CLK63 Black Series, which AMG openly admitted was inspired by Porsche's 911 GT3 RS. A bigger inlet manifold, new exhaust system and remap sharpened response and amped up the noise. Power was up to 507hp at 6,800rpm. Unchanged peak torque of 465lb ft was produced 250rpm higher at 5,250rpm. The usual Benz seven-speed auto was retained and reworked by AMG to quicken up the changes, which in hard use were smashed in with real urgency. A limited-slip differential with a discrete oil cooler and pump was added.
It had no back seat, but it had two proper racing buckets up front, a flat-bottomed (ish) steering wheel and a delicious little gear selector nubbin. It also had flared arches, multispoke lightweight 19in alloys, a 0-62 time of under 4.5secs and a delimited top speed of 186mph.
It's believed that no more than 700 CLK Blacks were made, and some say the number was actually below 600. Only 25 of them were in right-hand drive. The Black Series did 7m 52s around the Ring on a normal traffic day, helped by subtle but surprisingly effective aero. At around £100,000 it was as expensive as an M3 and RS4 combined. Simon Cowell bought a new Black Series in 2008. After it had had two more owners, that car sold in early 2019 for £95,000.
The standard CLK63 was between £65,000 and £70,000 when it came out, which was the same money as a Porsche 911 Carrera S. For that reason it was quite a rare sight on UK roads, and it's obviously even rarer now. With that in mind, prices as low as £12,000 today look more than reasonable, not just compared to the Black Series cars which still command prices in excess of £80,000 but especially against the £300,000-plus prices now being asked for the even racier 5.4 litre CLK AMG DTM, a £180k machine loosely based on Bernd Schneider's championship-winning CLK of 2003. It did the 0-62 in 3.9sec and ran on to 199mph. Just 180 DTMs were made, 80 of them (oddly) being Cabrios. Celebrity owners included F1 aces Jenson Button and Takuma Sato.
The undercarriage switch from C-Class to E-Class brought an end to production of the CLK63 in 2009, but that won't blot out the memory of an engine that created loads more drama than the supercharged V8 of the old CL55. Would a CLK63 therefore be a fitting Don Quixote-style lunge at the newly looming threat of total ICE shutdown by 2030? Maybe. Let's investigate - but only after we've bent down at the back for an eardrum-busting portion of V8 thunder and a hearty lungful of unburnt hydrocarbons.
SPECIFICATION - MERCEDES CLK 63 AMG (2006-on)
Engine: 6,208cc, V8
Transmission: 7-speed automatic, rear-wheel drive
Power (hp): 475@6,800rpm
Torque (lb ft): 465@5,000rpm
0-62mph: 4.6 secs
Top speed: 155mph (limited)
MPG: 19.9 (official combined)
Wheels: 7.5 x 18in (f), 8.5 x 18 (r)
Tyres: 225/40 (f), 255/35 (r)
On sale: 2006 - 2010
Price new: £65,215 (£68,815 Cabrio)
Price now: from £12,000
Note for reference: car weight and power data are hard to pin down with absolute certainty. For consistency, we use the same source for all our guides. We hope the data we use is right more often than it's wrong. Our advice is to treat it as relative rather than definitive.
ENGINE & GEARBOX
The M156 didn't produce quite as much power in the CLK as it did in the 503hp ML63. Some say this was because there wasn't quite enough room under the CLK's floor for a full dual exhaust setup. The CLK coupe did get quad tailpipes though, whereas the Cabrio only had two.
Even so, 475hp wasn't exactly weedy, and the 5,000rpm point at which maximum torque chimed in wasn't a major problem in practice either because a very acceptable 369lb ft was available from 2,000rpm. BMW's V10 M5 ran to 8,250rpm with smaller pistons, but it didn't feel as muscular as the Merc at lower revs.
As noted earlier, the M156 is a strong and reliable engine, but in every life a little rain must fall. There were issues, but today there are reasons to be cheerful. The thing to bear in mind with cars like this is that the vast majority of them will have been enthusiast-owned and maintained. As such, the fact that even the most recent CLK 63 is now ten years old is actually a good thing, because it means that most if not all of the common problems we're about to relate will have been addressed and rectified long ago. Well, you'd like to hope so anyway.
Perhaps the most widely documented M156 issue, particularly on early engines, were the cylinder head bolts (usually at the back of the engine) that would be corroded by coolant, stretched, and then, because of the amount of metal carved out by their Torx heads, broken off, leading in the worst case scenario to engine-grenading hydraulic lock.
Mercedes eventually recognised the issue, albeit four years after the engine made its debut. They replaced the bolts and valve lifters (buckets), which instead of spinning as they were supposed to would seize up and cause knock-on damage to the cam lobes that were made from softer metal. These problems tended to pop up when the engines had done around 100,000 miles. You can tell if a car has had the updated bits by comparing the engine number against a publicly available list.
One disgruntled New Jersey owner filed a class action lawsuit against Daimler, M-B and AMG on the grounds of valvegear defects. It was kicked out of court in 2011, but if a car you're looking at is showing a low coolant level warning light and/or an oddly high engine oil level, or if it has a misfire and white exhaust smoke beyond the warming-up stage, we wouldn't suggest hiring Rudy Giuliani to take up your cause but we would advise caution.
M156 rods can also be hydro-locked into odd shapes by stuck-open fuel injectors. Short of that, the bores could end up being washed clean, so it's good practice to replace the injectors every 60-70,000 miles. Camshaft adjusters can fail, signified by a cold-start rattle. So can idler pulleys and the magnesium alloy intake manifold. Other areas to keep an eye on are deteriorated crankcase breather valve diaphragms and hoses, and leaky gaskets for the valve cover, camshaft solenoid and oil filter housing. Engine and gearbox mounts wear out, which hardly surprisingly given the size of the chunks of metal involved. Sounds like a big list but, as noted, you'd think most if not all CLK 63s will have come out of the other side of all this by now.
Ongoingly, if that's a word, it's definitely a good idea to keep an M156's oil nice and fresh, especially when you remember that the design gives more oil to the exhaust cams than to the intake ones. Experts recommend halving the 10,000 miles change intervals recommended by Mercedes.
The seven-speed 7G-tronic auto gearbox (which was also new at the time) was controlled by wheel-mounted paddles. It was tweaked by M-B to inhibit change-ups at the red line unless you gave it permission to do so. There is some history of the transmission losing drive in this application. The conductor plate and valve body have been known to degrade, giving juddering and harsh downshifts in lower gears. Post-2009 CLKs were better. Driveshafts can get a bit weepy too.
As you might have guessed the CLK is in the highest road tax bracket, so that's a minimum of £580 a year to the Exchequer. Expect an average driving fuel consumption rate of around 18mpg.
CLKs of this generation had aluminium rear multi-link suspension (steel, not air) plus rack and pinion steering, the preceding W202 from the 1990s having had an inferior recirculating ball system. Don't expect laser-sharp handling, though. A 911 Carrera S would leave it for dead, but then again the CLK does have two proper rear seats. Mercedes saw fit to add a Sport Chrono-style lap timer function but it's thought that fewer than three owners have used it. Roll bar links and control arm bushes wear out.
Prior to the CLK 63's arrival there had been plenty of complaints about the fussiness of Mercedes' ESP system, so it was good news that the CLK gave you the option of disabling it, even if the traction control stayed on. No crossed-up powerslides, then, but there was a road-useful element of rear steer. A Quaife ATB (Automatic Torque Biasing) differential is money well spent if you're planning on remapping your CLL beyond the 500hp mark. They're about £500 a go, plus fitting.
The Black Series was quite a different animal. Its front track was 75mm wider, and the rear track 66mm wider. It had stiffer springs and dampers adjustable for compression and rebound. It was harder on the road than the regular CLK, but not upsettingly so. Grip was substantial enough to allow the driver to enjoy the Black's talkative steering and the ESP was relaxed still further to permit smoky drifts.
Give any big-engined car the beans and you'll be ripping through tyres at a rate of knots. Through a big operator like Blackcircles, one 225/40 Michelin Pilot Sport 4 for the front of a regular CLK 63 will cost about £105 fitted. Blackcircles wasn't offering a 255/35 PS4 for the one-inch wider back wheels at the time of writing, but a Conti SportContact S was just under £150 fitted.
These CLKs are getting on a bit now, so checking for rust is a must. The 209s were much better protected against corrosion than the 208s, and the CLK63s should be particularly good as they came along after a bunch of improvements had been made in 2004, but they're still going to need examining in the usual places, for example rear wheel arches, front wings, door bottoms and boot lid.
The keyless doors can break and so can the third brake light on the boot. Here's something that nobody has ever said about modern soft-tops (ahem): the electro-hydraulic mechanism for the Cabriolet's roof can play up. The hydraulic fluid level needs to be right, and it sometimes isn't because of faulty seals which start to give up after a decade or so, causing leaks in the rams and/or the pump. The reservoir is behind the carpeted nearside boot panel and is easy to check. If the level is OK, you'll have a problem with one of the hood's dozen or so microswitches. That's not so easy to check. The rear window can get loose in the hood too, allowing water in.
209 cabin quality is good, with just the odd rattle here and there that's usually from, but not limited to, the windows, which need to align properly for good wind sealing. Window regulators can give trouble.
Standard CLK63 kit included climate and cruise control, a six-speaker sound system, an electrically adjustable steering column and memory seats which didn't offer that much lateral support compared to the figure-huggers in a Black Series. The electric headrests can conk out as can the seat occupancy sensors. If air doesn't seem to be blowing out of the dash vents, the traditional 'just needs a regas' suggestion beloved of so many car sellers will be off the mark. It's more likely that the AC stepper motor or the plastic arms that control the vents need replacing. A click behind the dash when you turn on the ignition is a big clue that all is not well and you may end up having to remove most if not all of the dash to fix it.
Charmingly old-school options included a TV, rear window blind and, most stylishly of all, a ski-bag - though you'd want a good set of snow chains on if you were taking a 475hp rear-drive Merc to St Moritz. Other options were Bluetooth, Keyless Go, Distronic radar-based cruise control, Bose or Harmon Kardon Logic7 sound systems, heated/ventilated seats, Parktronic, sunroof, and bi-xenon headlights with cornering lighting. The sat-nav was Windows 98 tech and you should be grateful to see it missing. Seat bases get wobbly and the electronic 'butler' that hands you the seat belt can stop butlering.
Unlike some 6.2-engined Mercs, the CLK63 is not the sort of car you'll see parked up outside a nightclub with a 'B1G' registration plate. The coupe in particular has an under-the-radar elegance that will appeal more to the sort of bod who wants to pick and choose their time to make some noise.
There'll be nothing like this engine again. For that reason alone, you might think that the £12,000 price we've seen for a sub-100,000 mile, cleanly MOT'd and well historied specimen is more than fair exchange for the sound you get on startup, the growl as it hauls through the midrange and the indescribably satisfying din of a big handbuilt V8 hitting stupidly high revs.
In general, good coupes can be harder to find than average Cabrios. Our very unscientific impression is that soft tops seem to be a bit scruffier than the hardtops, which (again subjectively) do a better job of maximising the visual appeal of that windowless profile, especially in a strong colour like dark blue or black.
The privately owned £12k coupe we were talking about a minute ago was priced to reflect its 95,000 miles. Even so it was about £6k under the going rate despite it having had a hell of a lot of maintenance money spent on it. Maybe the owner was fed up with it, but we've seen cars with higher mileages carrying £20k-plus price tags. At that sort of money, you can certainly find 63s on the 'right' side of 50,000 miles.
Just under £26,000 will get you the papers to this late 2009 coupe with 45,000 miles. It's not massively optioned up, but it does have a full nine-stamp M-B service history.
If you want a Black Series, we can totally understand that because they are fabulous. Some rate the CLK Black as the best old AMG ever. They are available on the used market, but as they were only in production for two years (and fabulous) you'll pay hard for one. We saw a 24,000-mile 2007 car at ten quid under £87,000.
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