The Mercedes-AMG M156 engine is widely regarded as one of the best factory-built engines in the world. It is a V8 engine with a naturally aspirated design that first hit the market in 2006. Furthermore, the M156 engine was the last naturally aspirated V8 produced by Mercedes and AMG in concert, making it an important part of motorsports history.
The engine has a stellar reputation for both its superior design and its exceptional performance. At its peak, its power output was between 451 and 518 horsepower, allowing it to do a 0-60mph sprint in well under 4 seconds. The M156’s potent V8 was the result of substantial effort by AMG, making it stand out from the company’s other Mercedes offerings. The M156 was also a bridge between their supercharged V8s of the past and their turbocharged V6s and V8s of the future.
The M156’s background, specs, performance, reliability, and typical issues are all addressed in this comprehensive reference. Let’s start with a look at the origins of the incredible M156.
M156 Engine History
The AMG M156 was first introduced for the 2006 model year, despite having been under development since the early 2000s. It replaced the M113 engine, another illustrious Mercedes-Benz motor. The engine is a 6.2L V8, however it is really advertised as a 6.3L. This is done as a tribute to Mercedes’s first V8 engine, the 6.3L M100, which was used in production cars.
Two years in a row, in 2009 and 2010, the M156 was recognized as the best engine in the world for its exceptional performance. However, the M156 engine is not without its flaws. It suffers from dependability problems in a few places, especially the valve train, and the big 6.2L powerplant sucks gasoline like crazy. Most basic bolt-ons only provide marginal increases in power, therefore there is not a lot of aftermarket assistance, either.
Nonetheless, the M156 remained a reliable engine throughout its run in production, powering some wonderful vehicles like the W204 C63 AMG and W221 S63 AMG, and its M159 variation was used in the wildly popular SLS AMG from 2010 to 2015. AMG’s Affalterbach factory in Germany exclusively developed and constructed the M156. The M157 and M177 engines, a pair of smaller, bi-turbo V8s, eventually took its place due to their greater output.
Specifications
Specs for the 6.2L Mercedes M156 engine are as follows:
| Engine | M156 |
| Configuration | V8 |
| Displacement | 6.2L (6,208 cc) |
| Aspiration | Naturally Aspirated |
| Fuel System | Fuel Injection |
| Block/Head Material | Aluminum |
| Bore & Stroke | 102.2mm x 94.6mm |
| Valvetrain | DOHC 32V |
| Compression Ratio | 11.3:1 |
| Weight | 452 lbs |
| Horsepower Output | 451-518 hp |
| Torque Output | 465 lb-ft |
Applications
The M156 engine appeared in the following models:
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- 2007-2011 Mercedes-Benz E63 AMG
- 2007-2011 Mercedes-Benz ML63 AMG
- 2007-2011 Mercedes-Benz CLS63 AMG
- 2007-2010 Mercedes-Benz S63 AMG
- 2007-2010 Mercedes-Benz CL63 AMG
- 2007 Mercedes-Benz R63 AMG
- 2007-2009 Mercedes-Benz CLK63 AMG
- 2008-2011 Mercedes-Benz SL63 AMG
- 2008-2015 Mercedes-Benz C63 AMG
There was also a slightly modified higher power output version of the M156, the M159, which appeared in the following models:
- 2011-2015 Mercedes-Benz SLS AMG
- 2016+ Mercedes-AMG GT3
- 2020+ Mercedes-AMG GT3 Evo
M156 Engine Design
With a silicon-aluminum block and a compression ratio of 11.3:1, the M156 is a 6.2-liter V8 engine with water cooling. The block’s heat dissipation has improved and its weight has been reduced thanks to the silicon-aluminum alloy. The 32 intake (40mm) and exhaust (34mm) valves are controlled by dual overhead camshafts in this closed-deck layout. The engine has a cylinder bore of 102.2mm and a piston stroke of 94.6mm, and it is naturally aspirated.
In the M156, Mercedes pioneered the use of Nanoslide plasma coating on the cylinder walls. To create nanoslide, iron and carbon are melted together and sprayed onto the surface of the cylinder using a twin-wire arc spray method. As a result, the walls become much harder and smoother, with nearly a mirror-like polish, while the friction between them is drastically reduced. It’s a patented system developed specifically for AMG vehicles that promises a 50% reduction in drag. As a result, exhaust gas temperatures (EGTs) and wear are lowered while performance is maintained.
An electro-hydraulic cam adjuster allows for variable valve timing (VVT) in the motor. The crankshaft and connecting rods were both made of forged steel alloy, so they could handle high torque. With the exception of the C63 produced in 2010 and later, which has forged pistons and a racing-inspired lightweight crank, the M156 is equipped with cast hyper-eutectic pistons.
M156 vs M159
Mercedes-Benz introduced the M159, a new version of the M156, for the 2010 SLS AMG (E 63). The M159’s significant power boost was the consequence of various revisions to the vehicle’s layout. Performance was increased by redesigning and upgrading the valve train, intake, and headers. The dry-sump oiling system that replaced the M156’s wet-sump system contributed to the SLS AMG’s lower center of gravity, which improved the vehicle’s weight distribution and handling.
The Mercedes-AMG GT3, a high-end race car debuted in 2014, had the M159. Roughly 30 more horsepower were added, and the redline was increased, compared to the production model. Ten years after production stopped, the M159 is still being used in the 2020 GT3 Evo, proving it is a powerful and reliable option.
M156 Engine Performance
The M156’s exceptional effectiveness stands out above all else. The S63 AMG, E63 AMG, SL63 AMG, CL63 AMG, and CLS63 AMG all made 518 hp/465 lb-ft of torque by 2010, up from 451 hp/465 lb-ft when the engine first appeared in 2006. Strong pulling strength is present from idle to redline.
To say that AMG’s M156 is a worthy successor to the company’s racing pedigree would be an understatement. The V8’s impressive sound, quickness, and relatively high redline have all been praised in reviews. Even more impressively, certain models have been updated to reach astonishing redlines of 7,750 RPMs, which is quite a feat for such a potent V8 as is standard on most.
MBZ M156 Performance Upgrades
The M156 has incredible stock performance, but it lacks the aftermarket support of other Mercedes-Benz vehicles. The engine is unresponsive to intake upgrades since the factory intake provides ample amounts of both flow and cold air. The only tried and true intakes retail for more than $2,000 and produce a paltry 10whp at best.
Tuning, exhaust headers, and forced induction are the only worthwhile upgrades for the M156. Forced induction is the best way to get the most power out of your engine, but supercharger systems are pricey and the installation process is complicated. Exhaust headers and tuning are the most effective methods for those interested in street builds or moderate gains in power.
Tuning can be purchased as part of a staged power package or individually, and will normally add 40-50 horsepower and 20-30 lb-ft of torque to a factory motor. Local tune seekers should ask their prospective tuner what method they recommend.
The M156 is offered with either a short-tube or a long-tube exhaust header. Long-tube headers are available with or without cats to replace the restrictive stock exhaust system. It’s important to remember that catless exhausts can’t be legally used on public roads, so non-racing builds should utilize either shorty headers or high-flow catted alternatives. When comparing the gains of long- and short-tube headers, you may expect the former to yield 25-40 whp and the latter to yield 15-20 whp.
Throttle bodies and catbacks are two more popular upgrades for the M156. The average increase in horsepower with a throttle body is 10–13 hp, with a catback adding at most 5 hp. Incorporating a tuning package and new exhaust headers into your throttle body setup will maximize its benefits. Due to the fact that everyone has different aural preferences, catbacks are an excellent way to modify the M156’s exhaust sound.
Mercedes M156 Power Limits
It’s hard to find a more rugged engine than the M156. Incredibly, the stock bottom end can easily handle 750-800 horsepower, which is much beyond the capabilities of any street-legal builds. With its closed deck construction and specially designed pistons, the block can take a lot of punishment and generate a lot of power without showing any signs of wear.
M156 Engine Common Problems
There is no doubt that the M156’s bottom end can manage massive amounts of power, but the M156 is not the most reliable AMG engine. There are several valve train components and the head bolts that are defective straight from the factory. Problems can arise even in entirely stock vehicles, and if you’re out of warranty, the repairs might get pricey fast.
Common M156 engine problems:
- Head Bolts
- Camshaft Lobes
- Camshaft Adjuster Plates
- Lifters
The valve train, and the camshaft in particular, accounts for the vast majority of the problems. The updated design was meant to fix everything, however there were still difficulties, some of which we will discuss below. The M156 has 4 cams, which means that maintenance and repair expenditures will quickly add up. A lawsuit was filed against the manufacturer of the engine because of problems with the valve train.
M156 Lawsuit
Frustrated AMG owners filed a class action lawsuit against Mercedes in 2011, far after the M156 had been on the road for half a decade, due to issues with the engine’s valve train, notably the steel valve lifters and cast nodular camshafts. A complaint claimed that components wore out and broke more quickly than normal because they were defective. The plaintiffs contend that AMG knew about the problems in 2007, but did nothing to fix them.
In 2012, the court ruled that the plaintiffs lacked the legal right to pursue damages in court, and the complaint was subsequently dropped without a settlement or admission of liability on AMG’s part. However, AMG may have known there was a problem with the M156 lifters because they were altered for the 2011+ M156 (the only vehicle to use the M156 after 2011 was the C63 AMG). The head bolts, which had been problematic for a long time, were also fixed as part of the makeover.
1) Mercedes M156 Head Bolt Problems
For the M156 engine, loose head bolts were the most common issue before the 2011 refresh. In a nutshell, the original head bolts were poorly made and prone to corrosion, which led to erosion and coolant leakage through the cylinder heads. The bolt heads would shear off entirely in some instances.
Thick white smoke from the exhaust, low coolant levels, and milky-colored oil are all signs of worn or cracked head bolts. White smoke and coolant loss are caused by the coolant getting into the engine and being burned off. The oil has turned a milky white because coolant is spilling into it.
Factory-installed upgraded head bolts on M156s manufactured in 2011 and later fix the problem. If your M156’s head bolts keep breaking, it’s time to update to the newer, more reliable OEM bolts. Head studs are another option to think about if you plan on pushing extreme power levels.
2) M156 Lifter Issues
The M156’s steel valve lifters are the source of most of the problems with the valve train. Those were at the center of a lawsuit in 2011 for reasons that are now easy to see. Lifters are actuated by the camshaft lobes to open and close the intake and exhaust valves of the cylinders. However, M156 lifters have been known to entirely seize up due to oiling concerns. Because the cam lobes only strike one spot over and over, this would lead them to wear out quickly.
CELs and limp mode might occur from misfiring and spark difficulties that are brought on by lifters that have become frozen. To prevent the lifters from wearing out too quickly and seizing up, Mercedes eventually revised their design to improve oiling. However, opinions on them are diverse, with some saying they did not improve matters at all.
The remedy to the lifters issue is to either get the upgraded component from AMG, or, if you do not trust it to work, the lifters out of the M159, the M156’s relative, can be utilized. The M159 black series lifters are also coated with a material that drastically cuts down on friction and wear. Because of how much lighter they are compared to the original, performance is also greatly improved. If you need to replace your head bolts, one alternative to consider is switching to M159 lifters instead of the original equipment.
3) MBZ 6.2L V8 Worn Camshaft Lobes
Another problem with the M156’s valve train is worn cam lobes, which are connected to the lifter malfunction. As with the lifters, the cam lobes have lubrication concerns due to poor oiling design. Another issue was the lifters’ tendency to seize in position and wear the top of the cam lobes. This could lead to significant scoring and, in extreme situations, could even destroy the cam lobes.
Increased ticking sounds from the valve train, especially on cold starts, are a sign of worn camshaft lobes. Additionally, if the problem is not addressed, it could lead to misfires and spark troubles in addition to the lifters.
In the case of worn cam lobes, two options exist. Adding a lubricating additive, such as Ceratec or MOS2, is the quickest, easiest, and least expensive option. While helpful, this approach only serves as cosmetic surgery rather than addressing the root cause. The only method to completely get rid of the issue is to replace the stock camshafts with a set of aftermarket camshafts that are built to last and perform better. Even for those thinking about installing forced induction on an M156, there are a number of alternatives to choose from.
4) Worn Camshaft Adjuster Plates
Camshaft adjuster plates are the last major problem with the M156 valve train. Cam adjusters regulate the engine’s variable valve timing (VVT), which has significant effects on fuel economy and performance. But the M156’s cam adjusters frequently failed. Tolerance breakdown between the plates would lead to oiling problems and excessive wear.
Worn cam adjuster plates can cause a rattling noise at startup, a drop in gas mileage, a sluggish throttle response, and misfire or VVT error codes. As a matter of fact, Mercedes-AMG has issued a factory service bulletin about the cam adjuster plates. The M156-equipped models from every year were included, as were the post-facelift C63 AMGs, whose drivers continue to experience similar problems.
Worn plates can be fixed by switching to new OEM plates or by using aftermarket plates. Even if you replace with OEM, the original problem may return after some time. Stronger and more long-lasting replacement plates for the M156 can be found from 63Motorsports.
M156 Engine Summary
The M156 is an exceptionally potent engine with a solid foundation. It has a V8 engine that churns out a thundering, raspy sound to match the 500+ hp it uses to rip through the pavement. It was featured in the W204 C63 AMG and SLS AMG, two of the best-reviewed Mercedes models of the past decade.
However, there are some problems with the engine. The head bolts on models produced before 2011 were poorly made and prone to leaking. Numerous problems were present in the valve train as well, particularly with the lifters, cam lobes, and cam adjuster plates. Mercedes admitted that there were problems, but their solutions were inadequate (with the exception of the head bolts).
Drivers still give the M156 high marks for its performance and ability to handle a lot of power. The fact that Mercedes-AMG is still using it in the 2020 GT3 Evo indicates how well-designed and respected it is. Despite the fact that it does not react well to most bolt-ons, it is still possible to get fairly notable increases with the installation of exhaust headers and some careful tweaking.
