Mercedes M156 Engine Guide
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The Mercedes-AMG M156 engine has a sizable reputation as one of the company’s most well built production motors. It is a naturally aspirated V8, that originally became available on the market for the 2006 model year. It was also the final naturally aspirated V8 that Mercedes and AMG built together, making the M156 engine a true piece of racing history.
The engine is well known for its impeccable design and outstanding performance. It ranged from 451-518hp at its most powerful, and could easily make a 0-60 sprint in under 4 seconds. AMG worked extensively on the M156 to create a unique, powerful V8, and it is truly unlike most other Mercedes engines. In addition, the M156 also marked a transition between their previous generation of supercharged V8s and their upcoming generation of turbocharged V6s and V8s.
This guide will cover everything you need to know about the M156, including its history, specifications, performance, reliability, and common problems. First, let’s take a look at the history behind the creation of the awe-inspiring M156.
M156 Engine History
AMG designed the M156 in the early 2000s and it made its debut for the 2006 model year. It was the successor to the M113 engine, another highly respected Mercedes-Benz engine. The engine is a 6.2L V8, but it is actually marketed as a 6.3L. This is to pay homage to the first mass-production V8 that Mercedes ever created, the 6.3L M100 engine.
The M156 won the international engine of the year award in both 2009 and 2010, a testament to its outstanding performance capabilities. However, the M156 is far from a perfect engine. It suffers from reliability problems in a few areas, especially the valve train, and the massive 6.2L powerplant drinks gasoline like crazy. It also does not have a huge level of aftermarket support, as most simple bolt-ons only offer minimal power gains.
Still, the M156 was a solid engine during its production span, and it powered some fantastic cars, including the W204 C63 AMG, W221 S63 AMG, and its M159 variant was found in the ultra popular SLS AMG from 2010-2015. AMG’s Affalterbach plant in Germany exclusively developed and built the M156. Eventually, it was replaced with the M157 and M177 engines, two smaller, bi-turbo V8s that both produced more power.
Specs for the 6.2L Mercedes M156 engine are as follows:
|Displacement||6.2L (6,208 cc)|
|Fuel System||Fuel Injection|
|Bore & Stroke||102.2mm x 94.6mm|
|Horsepower Output||451-518 hp|
|Torque Output||465 lb-ft of torque|
The M156 engine appeared in the following models:
- 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
The M156 is a water-cooled, 6.2L, V8, with a 11.3:1 compression ratio and silicon-aluminum block. The silicon-aluminum alloy has decreased weight while allowing the block to easily shed heat. It is a closed deck design, with dual-overhead camshafts controlling 32 intake (40mm) and exhaust (34mm) valves. The engine is naturally aspirated with a cylinder bore of 102.2mm and a piston stroke of 94.6mm.
Notably, the M156 was the first Mercedes engine to have the cylinder walls plasma coated with Nanoslide. Nanoslide is a twin-wire arc spray process where iron and carbon are melted together onto the surface of the cylinder walls. This creates hardened walls while seriously reducing friction, making them stronger and smoother, and producing almost a mirror like finish. It is an AMG-exclusive technology that they claim reduces friction by as much as 50%. This has the effect of lowering cylinder temperatures, which reduces EGTs and wear while sustaining performance.
The engine also added variable valve timing (VVT) controlled by an electro-hydraulic cam adjuster. It came with a forged steel alloy crankshaft and beefy connecting rods capable of withstanding lots of power. The M156 also has cast hyper-eutectic pistons, except the 2010+ C63, which has forged pistons and a lighter racing inspired crank.
M156 vs M159
For the 2010 SLS AMG, Mercedes-Benz released a variant of the M156, the M159 (E 63). The M159 featured a large power increase as the result of several design changes. The valve train, intake, and headers were all redesigned and improved for performance. Also, a dry-sump oiling system replaced the wet-sump system from the M156, which lowered the SLS AMG’s center of gravity and allowed for better weight distribution and handling.
The M159 even appeared in the Mercedes-AMG GT3, a high spec race car first introduced in 2014. The redline was raised and about 30 horsepower were added to it over the production version. The M159 was still being used in the 2020 GT3 Evo, showing it is still a more than capable engine a decade after its original production ended.
M156 Engine Performance
By far the most memorable part of the M156 is its outstanding performance. When the engine debuted in 2006, it made 451hp/465tq, and by 2010 the S63 AMG, E63 AMG, SL63 AMG, CL63 AMG, and CLS63 AMG all made 518hp/465tq. It features a robust power band that pulls hard all the way to redline.
The M156 is a true heir to the racing heritage of AMG. Reviewers praise the incredible sound of the V8, as well as its responsiveness, and relatively high redline. For most models, the standard redlines is 7,250 RPMs, but some have been upgraded to go as high as 7,750 RPMs – pretty incredible for such a high-powered V8.
MBZ M156 Performance Upgrades
While the M156 delivers jaw-dropping performance from the factory, it does not have the same level of aftermarket support as many Mercedes-Benz models. The engine does not respond very well to intakes, as the stock intake already flows very well and delivers cool enough air. The only proven intakes cost north of $2,000, and only really deliver 10whp at the most – hardly a worthwhile investment.
The only modifications truly worth doing to the M156 are tuning, exhaust headers, and forced induction. Forced induction will obviously generate the biggest amount of power, but supercharger kits are expensive and it is far from a simple modification. For anyone looking at street builds or more moderate power increases, exhaust headers and tuning are the best options.
Tuning will typically net about 40-50whp and 20-30wtq on an otherwise stock motor, and can be bought as part of staged power packages or on their own. For those looking at local tuning, it’s best to consult with your tuner about what option they prefer.
Exhaust headers on the M156 come in two types, either short-tube or long-tube style. Long-tube headers replace the cats in the OEM exhaust, and can be had either catless or with high flow cats. Keep in mind, catless exhausts are illegal for street use, so any non-competition builds should stick with shorty headers or high flow catted options. Long-tube headers will net about 25-40whp, while short-tubes will gain about 15-20whp.
Other common mods on the M156 are throttle bodies and catbacks. Throttle bodies add about 10-13hp, and catbacks maybe 5hp at the most. Throttle bodies will offer better gains when used in conjunction with tuning and exhaust headers. Catbacks are great for shaping and refining the exhaust tone of the M156, as sound is really down to personal preference.
Mercedes M156 Power Limits
The M156 is a remarkably stout engine. The stock bottom end is capable of withstanding 750-800hp easily, something well beyond the purview of any street-based builds. Most combinations of bolt-ons will not come close to challenging the block or internals’ limits, as the unique piston design and closed deck block stand up incredibly well to abuse and power.
M156 Engine Common Problems
While the M156’s bottom end is able to handle gobs of power thrown at it, overall reliability is not the greatest for an AMG engine. From the factory, there are issues with the head bolts and multiple valve train components. Even on completely stock cars issues can occur, and out of warranty they can be pretty expensive fixes.
Common M156 engine problems:
- Head Bolts
- Camshaft Lobes
- Camshaft Adjuster Plates
Most of the issues are related to the valve train, and the camshaft specifically. The face lifted design was supposed to take care of the problems, but only part of the issues were addressed – which we will get into later. Exacerbating the problem, the M156 has 4 cams, which means that replacement costs quickly become compounded. The engine was even the subject of a lawsuit over defects in their valve train components.
In 2011, after the M156 had been in circulation for half a decade, upset AMG owners filed a class action lawsuit against Mercedes over the engine’s valve train problems, specifically the steel valve lifters and cast nodular camshafts. The lawsuit claimed these parts were defective which had led to increased premature wear and failure. The claimants suggested AMG was aware of the defects since 2007 but did not move to rectify them.
Eventually, in 2012, the lawsuit was dismissed due to lack of standing, and there was no settlement and AMG admitted no wrongdoing. However, the 2011+ M156 (the only models to continue to use the M156 after 2011 was the C63 AMG), did get revised lifters – possibly indicating that AMG did know there was an issue with them being defective. The facelift also rectified issues with the head bolts, which had long been an issue.
1) Mercedes M156 Head Bolt Problems
The number one problem with the M156 engine prior to the 2011 facelift was head bolts. Basically, the original head bolts were poorly designed and were therefore easily susceptible to corrosion, which caused the bolts to erode and leak coolant into the combustion chamber through the cylinder heads. In some cases, the tops of the bolts would completely break off.
The symptoms of worn or broken head bolts are thick white smoke from the exhaust, low coolant levels, and milky colored oil. The white smoke and loss of coolant comes from the coolant entering the engine and getting burned off. The milky color of the oil indicates the presence of coolant leaking into it.
For 2011+ models, the M156 has updated head bolts from the factory, rectifying the issue for those engines. Anyone experiencing head bolt failure on their M156 should upgrade to the revised OEM head bolts. Of course, if you are planning on pushing extreme power levels, head studs should probably be considered, too.
2) M156 Lifter Issues
The biggest issues with the M156 valve train are the steel valve lifters. These were the subject of the 2011 lawsuit, and in hindsight it is pretty obvious why. The purpose of lifters is to close and open the intake or exhaust valves on the cylinders, and they are controlled by the camshaft lobes. However, the M156 lifters are known in some cases to completely seize up due to oiling issues. This would cause premature wear on them due to the cam lobes repeatedly only hitting one area.
Subsequently, seized lifters can eventually lead to misfiring and spark problems, resulting in CELs and limp mode. Eventually, Mercedes updated the design on the lifters to allow for better oiling to eliminate the problem of premature wear and seizing. However, these have been given mixed reviews, with some claiming they did not alleviate the problem at all.
The solution to the lifters issue is to either get the updated part from AMG, or, if you do not trust that to work, the lifters out of the M159, the M156’s cousin, can be used. In addition, the M159’s black series of lifters have a specific coating to reduce friction and wear. They are also much lighter than stock, which allows for increased performance. Many people will swap out their OEM lifters for ones out of the M159 when they replace their head bolts, so that is an option to keep in mind if you experience head bolt issues.
3) MBZ 6.2L V8 Worn Camshaft Lobes
Worn cam lobes are another valve train issue on the M156, and they are related to the issue with the lifters. The cam lobes, similar to the lifters, also suffer from oiling design issues which impact lubrication. This was compounded by the problems with the lifters, which, once seized in place, would wear the top of the cam lobes. This could cause severe scoring, and in some cases would compromise the cam lobes entirely.
Symptoms of worn camshaft lobes are increased ticking noises from the valve train, especially on cold starts. In addition, if the issue gets severe enough, it could cause misfires and spark issues along with the lifters.
There are two possible solutions to worn cam lobes. The quickest, easiest, and cheapest solution is to add a lubrication additive, like Ceratec or MOS2. However, this solution is really more of a battle dressing than anything, and does not really solve the heart of the issue. The only way to truly eliminate the problem is to buy an aftermarket set of camshafts that are stronger and better designed than OEM. There are several available options on the market, even for those looking at adding forced induction to their M156.
4) Worn Camshaft Adjuster Plates
The final plague of the M156 valve train are the camshaft adjuster plates. Cam adjusters are responsible for controlling the variable valve timing (VVT) on an engine, and are incredibly important for things like gas mileage and performance. However, on the M156, the cam adjusters frequently had issues. The plates would fall out of tolerance and cause issues with oiling, which would lead to lots of premature wear.
Symptoms of worn cam adjuster plates are a loud rattling sound at startup, sudden negative changes to fuel economy, poor throttle response, and misfire and VVT codes. Mercedes-AMG actually released a factory service bulletin addressing issues with the cam adjuster plates. It covered every single model year and model that contained the M156 – including post-facelift C63 AMGs, which drivers still report suffer from these issues.
The fix for worn plates is to either replace them with OEM or go with aftermarket solutions. Replacing with OEM will likely, but not always, lead to the same issue occurring again after a period of time. Aftermarket wise, 63Motorsports has several versions of plates for the M156 that are stronger and more durable than stock.
M156 Engine Summary
Overall, the M156 is an incredibly powerful engine that has a very well engineered bottom end. It produces a throaty V8 tone that sounds thunderous and raspy, to go with the 500+hp engine that screams down the streets. It has appeared in some of the most well reviewed Mercedes of the last decade, including the W204 C63 AMG and SLS AMG.
Yet, the engine is not without its issues. Pre-2011 models featured poorly designed and manufactured head bolts that were prone to leaking and breaking. The valve train also had several issues, especially with the lifters, cam lobes, and cam adjuster plates. Mercedes acknowledged several of these issues, but their fixes were less than adequate (with the exception of the head bolts).
Still, the M156 is a standout engine that drivers praise for its performance and ability to handle lots of power. The fact that Mercedes-AMG still uses it in the most recent iteration of their GT3 Evo in 2020 shows just how respectable and well designed it truly is. While it does not respond great to most bolt-ons, exhaust headers and tuning can still produce some pretty noticeable gains.
What’s your experience with models containing the M156? Are you considering buying a C63 AMG or E63 AMG equipped with the M156?
Let us know in the comments below!