Common Mercedes M157 Engine Problems
Mercedes-M157 Benz’s engine is a 5.5-liter twin-turbo V8 that was introduced in 2011 AMG models. It generates an incredible 518-577 horsepower, depending on the model and AMG Performance Package. A tune and bolt-on boost the M157 engine’s performance even further. That is to say, Mercedes’ M157 AMG engine is anything but a slouch. With this much power, how reliable is the M157?
Mercedes M157 AMG Engine
Mercedes-Benz models equipped with this potent Mercedes AMG engine include the following:
- 2012-2016 E63 AMG
- 2011-2017 S63 AMG
- 2011-2014 CL63 AMG
- 2012-2018 CLS63 AMG
- 2012-2015 ML63 AMG
- 2013-2018 G63 AMG
- 2012-2016 GL63 AMG
- 2015-2019 GLE63 AMG
- 2016-2019 GLS63 AMG
Mercedes M157 Common Problems
In general, the M157 is a dependable engine, but it is not bulletproof. However, Mercedes’ M157 engine is quite good for a high-performance engine. The following are five of the most common M157 engine problems, in no particular order:
- Timing Chain
- Spark plugs
- Valve Timing Cover Leak
- Coolant hoses
The remainder of this article will discuss these five common M157 issues in greater detail. We’ll discuss a few of the warning signs and symptoms associated with each of the problems.
1. Mercedes M157 AMG Timing Chain Problems
We figured we’d start with the M157 timing chain discussion, as it’s primarily a problem with early model M157 engines. On initial start-up, the 2011 and 2012 model M157 AMG engines have an issue with oil drainage from the cylinder head.
This results in a brief oil deficiency in the timing chain tensioner. Eventually, this causes the timing chain to stretch, necessitating timing chain replacement. Later model M157 engines included a check valve to prevent oil starvation.
On 2013+ M157 AMG engines, a revised timing chain tensioner and guides were also installed. As such, the timing chain issues affect primarily 2011 and 2012 models.
M157 Stretched Timing Chain Symptoms
Several common symptoms of M157 AMG63 timing chain problems include the following:
- Long cranks
- Misfires and power loss
- CEL illuminated
- Fault codes
This is not an exhaustive list of all possible symptoms of a timing chain failure on an M157. Additionally, if you exhibit these symptoms, it does not necessarily mean that the timing chain is to blame. Keep an eye out for error codes. Generally, if the M157 is experiencing timing chain issues, fault codes will be stored.
M157 Timing Chain Replacement
This can be an extremely costly repair. Mercedes did, however, replace the components with revised versions and install the check valves in response to owner complaints. However, there was no official recall for it. Expect to pay well over $1,000 for this repair at the dealer or an independent shop.
The good news is that it is 2020. Timing chain failures were discovered on early model M157 engines. As a result, it is likely that a large proportion of the timing chains that would fail have already failed. It’s still something to be aware of, as it can be a time-consuming and costly repair.
2. Mercedes M157 AMG Spark Plug “Problems”
To be sure, spark plugs should not be considered a serious issue. Especially for those of us who come from the BMW world, where we are accustomed to constant spark plug changes. Turbocharged engines are notorious for consuming spark plugs, and the M157 AMG63 engine is no exception. It’s all part of the package when you own a high-performance twin turbo engine.
This is especially true for M157 engines that have been tuned or modified. On stock M157 engines, spark plugs should be replaced every 40,000 miles. M157s that have been tuned may require replacement every 15,000–25,000 miles.
M157 engines that have been tuned or modified frequently exhibit misfire issues with the OEM spark plugs. A spark plug gap that is too large in combination with increased cylinder pressures may result in spark blow out.
Eventually, the spark blows out, resulting in cylinder misfires. Additionally, on heavily tuned and modified M157 engines, colder spark plugs may be required to prevent pre-ignition.
M157 Spark Plug Symptoms
Spark plugs are a required component of standard maintenance on stock M157 engines. Over time, the plugs lose their effectiveness, resulting in misfires and a variety of other noticeable problems. Several symptoms of worn-out spark plugs include the following:
- Rough idle and/or stuttering acceleration
- Power loss
- Reduced fuel economy
Misfires are typically the M157’s first symptom. Old, worn spark plugs simply cannot generate a large enough spark to complete the combustion process.
If the spark plugs are sufficiently worn, you will notice significant power loss, a stuttering idle, and stuttering acceleration (due to the misfires). We recommend replacing all eight M157 spark plugs concurrently.
M157 Spark Plug Replacement
Fortunately, if you avoid the dealer, M157 spark plugs are reasonably priced. Purchase a set of OEM spark plugs from a reputable online retailer.
A set of eight OEM spark plugs can be found for less than $100, and the installation is straightforward. Replacing the spark plugs requires some maneuvering in tight spaces, but it’s a fairly straightforward do-it-yourself project.
M157 Spark Plug Replacement Intervals:
- Stock – 40,000-50,000 miles
- Tune only – 20,000-30,000 miles
- Heavily modded – 15,000-20,000 miles
M157 Spark Plugs for Tuned, Modded Engines
As previously stated, spark plugs may be more difficult to install on modified M157 engines. OEM spark plugs should suffice for the majority of stock turbocharged vehicles. However, if you’re experiencing misfires, you can try gapping the plugs down slightly.
A smaller gap between the spark plugs results in a more intense spark needed to burn the increased air/fuel mixture. To be clear, reducing the gap between the spark plugs reduces the life of the spark plugs.
We recommend colder spark plugs for heavily modified M157 engines. Plugs that are colder are more efficient at dissipating heat away from the spark plug tip. This is critical because an overheated spark plug can result in pre-ignition and engine knocking.
This is a recipe for blown motors, even more so when heavily modified. Many of us BMW enthusiasts have had great success with 1 or 2 step colder spark plugs.
3. Mercedes M157 AMG Valve Timing Cover Leak
The M157, also known as the timing case cover, is prone to valve timing cover leaks. Oil and/or coolant may leak from the front valve timing cover’s drain hole. Typically, this leak is caused by the timing case cover failing to seat properly. Mercedes-Benz issued a service bulletin addressing this specific issue, which is depicted below.
According to the service bulletin, the M157 timing case cover is typically repairable without the need for replacement components. Repeal the cover by simply resealing it. However, given the labor-intensive nature of the job, it may be prudent to replace the components while you’re in there.
M157 Timing Case Cover Leak Symptoms
A visible oil or coolant leak from the timing case cover area is the primary symptom of a leaking timing case cover. Often, the leak is small and goes unnoticed. If the leak is severe enough, you may notice smoke or the odor of burning fluid.
M157 Timing Case Cover Replacement
As previously stated, it appears that re-sealing the M157 timing case cover frequently works well without requiring replacement parts. You can save some money by taking this route. However, the M157 valve covers must be removed in order to access the timing case cover. As such, it is a labor-intensive job that can be quite costly at the dealer or an independent repair shop.
Finally, if you are a skilled do-it-yourselfer, we recommend saving your money and attempting the re-sealing yourself. If the work is performed at a repair shop, you may wish to err on the side of caution and completely replace the timing cover.
4. Mercedes M157 AMG Coolant Hose Leaks
We are very familiar with coolant hose leaks, and well, all coolant leaks in general, having come from the BMW world. The M157 coolant hoses are prone to splitting, cracking, or simply popping loose as they age and accumulate mileage. Coolant hoses are typically simple to repair and do not require much attention. However, extreme caution should be exercised if the leak is severe enough to result in rapid coolant loss.
Overheating wreaks havoc on an engine and may necessitate costly repairs. When the engine’s coolant is depleted, the engine rapidly heats up. Consider towing the vehicle home or to a repair shop if the coolant loss is severe. If the leak is not severe, simply top it off with coolant to transport it to a location for inspection and repair.
M157 Coolant Hose Leak Symptoms
In most cases, the symptoms of a coolant leak are obvious. Minor M157 coolant hose leaks will most likely result in a few coolant drops under the car and an eventual low coolant warning. Significant M157 leaks will manifest themselves in more obvious ways, including the following:
- Coolant under engine area
- Rapid overheating
- Low coolant light
Again, coolant hose leaks are typically not a cause for concern. However, it is critical to monitor the rate of the leak. The M157 will overheat in minutes if there is insufficient coolant.
M157 Coolant Hose Replacement
Depending on which hose(s) is leaking, these are typically fairly straightforward and inexpensive repairs. The majority of coolant hoses cost less than $75 and are relatively simple to repair on your own. Given the low cost of the hoses, it may make sense to replace any hoses in the general area on a preventative basis. Particularly as the M157 ages and the miles add up.
Mercedes M157 Common Problems & Reliability Summary
As previously stated, the M157 is an extremely reliable engine in general. Expect reliability and repair costs comparable to Honda, but the M157 is unquestionably more reliable than many high-performance engines on the market.
The timing chain, spark plugs, valve timing cover, and coolant hoses are all examples of common problems. Naturally, this is not an exhaustive list of possible problems with the M157.
As the M157 ages, more “common problems” are likely to surface. That is the natural aging process of high-performance engines. Regardless, the Mercedes M157 AMG engine is a beast. With a whopping 500+hp and a respectable reliability record, the M157 is difficult to fault.