The Mercedes M157 engine is a 5.5L twin-turbo V8 first released in 2011 AMG models. It produces an astounding 518-577hp, depending on the model and AMG Performance Package. However, no engine is perfect and that applies here, too. The M157 is prone to its share of problems including the timing chain, timing cover, spark plugs, and coolant hoses. In this article, I discuss these common M157 problems along with symptoms and replacement.
Cars That Use the Mercedes M157 AMG Engine
This powerful Mercedes AMG engine is featured in the following Mercedes-Benz models:
- 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
Common Mercedes M157 Problems
Overall, the M157 is a reliable engine, however it’s not bulletproof. Though, it’s pretty darn good considering it’s a high-performance engine. Some of the most common M157 engine problems include:
- Timing Chain
- Spark plugs
- Valve Timing Cover Leak
- Coolant hoses
Throughout the remainder of the article I will briefly discuss these common M157 issues. I will also include a few warning signs and symptoms of each of the problems.
1) Timing Chain Problems
Timing chain problems are predominately an issue on early model engines. 2011 and 2012 model M157 AMG engines have a problem with oil drainage from the cylinder head on initial start-up. This leads to brief oil starvation of the timing chain tensioner. Ultimately, this causes the timing chain to stretch and then requires that the timing chains be replaced. Later model engines had a check valve installed to prevent the oil starvation issues. A revised timing chain tensioner and guides were also installed on 2013+ M157 AMG engines. As such, it is mostly 2011 and 2012 models affected by the timing chain problems.
Stretched Timing Chain Symptoms
A few common symptoms of M157 AMG63 timing chain issues include:
- Long cranks
- Misfires and power loss
- CEL illuminated
- Fault codes
This is not an exhaustive list of all potential symptoms of an M157 timing chain issue. Additionally, if you have these symptoms it does not mean it is definitely the timing chain. Be on the lookout for fault codes. Generally, fault codes will be stored if the engine is experiencing timing chain issues.
Timing Chain Replacement
This can be a rather expensive repair. However, Mercedes did replace the components with the revised versions and installed the check valves when owners experienced issues. There was no official recall for it, though. Expect this repair to run well over $1,000 at the dealer or an indy shop. However, the good news is it’s 2020. The timing chain issues were on early model M157 engines. As such, it’s likely a lot of the timing chains that would fail have already done so. It’s still something to be aware of since it can be a labor intensive, costly repair.
2) Spark Plugs
OK, spark plugs shouldn’t be truly considered a problem. However, forced induction engines love burning through spark plugs and the M157 AMG63 engine is no exception. It’s simply a part of owning a high performance twin turbo engine. This is especially true on tuned and modded engines. Expect to replace spark plugs every 40,000 miles on stock M157 engines. Tuned engines may require replacement as often as every 15,000-25,000 miles.
Tuned and modded M157 engines frequently experience misfire issues on the OEM spark plugs. Too large of a spark plug gap coupled with higher cylinder pressures may result in spark blow out. Ultimately, the spark blowing out leads to cylinder misfires. Additionally, colder spark plugs may be required to prevent pre-ignition on heavily tuned and modded M157 engines.
M157 Spark Plug Symptoms
Even on stock engines, spark plugs are a part of standard maintenance. Over time, the plugs lose effectiveness and cause misfires among several other noticeable issues. A few symptoms of old, worn spark plugs include:
- Rough idle and/or stuttering acceleration
- Power loss
- Reduced fuel economy
Misfires are generally the first symptom the M157 will experience. Old, worn spark plugs simply will not create a large enough spark to result in a complete burn. If the spark plugs are bad enough you will notice significant power loss, rough idle, and stuttering acceleration (due to the misfires). We recommend changing all 8 spark plugs at the same time.
Spark Plug Replacement
Fortunately, M157 spark plugs are relatively inexpensive if you avoid the dealer. Pick up a set of OEM spark plugs online from a reputable website. A set of 8 OEM spark plugs can be found for less than $100 and it’s a simple DIY. Replacing the spark plugs requires working in some tight areas but it’s a pretty basic DIY.
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
Spark Plugs for Tuned, Modded Engines
As we mentioned briefly, spark plugs may be a bit trickier on modified M157 engines. OEM spark plugs should suffice for most stock turbo cars. However, you may try gapping the plugs down a bit if you’re experiencing misfire issues. A smaller spark plug gap will create a more intense spark required to burn the increased air/fuel mixture. To note, decreasing the spark plug gap will reduce the spark plugs life.
For heavily modded M157 engines we recommend opting for a colder spark plugs. Colder plugs are more effective at transferring heat away from the spark plug tip. This is important because a spark plug that becomes too hot may result in pre-ignition and engine knocks. A recipe for blown motors, especially when heavily modded. A lot of us BMW guys run 1 or 2 step colder spark plugs with great success.
3) Valve Timing Cover Leak
Also referred to as the timing case cover, the M157 is prone to valve timing cover leaks. Oil and/or coolant may leak from a drain hole located on the front valve timing cover. This leak is typically caused by the timing case cover not seating properly. Mercedes actually issued a service bulletin for this exact issue, imaged below.
Per the service bulletin, the M157 timing case cover is typically serviceable without replacement parts. Simply re-seal the cover. However, it is a somewhat labor intensive job so it may make sense to replace the parts while you’re in there.
Timing Case Cover Leak Symptoms
The main symptom of a leaking timing case cover is a visible oil or coolant leak from the timing case cover area. Often the leak is minor and may even go unnoticed. However, if the leak is bad enough you may notice smoke or smell burning fluid.
Timing Case Cover Replacement
As mentioned briefly, re-sealing the M157 timing case cover often works well without the need for any replacement parts. You can opt to save a bit of money and go this route. However, you do need to remove the valve covers in order to access the timing case cover. As such, it’s a labor intensive job which is fairly expensive at the dealer or an independent repair shop.
Ultimately, if you are a savvy DIY’er we recommend saving the money and attempting the re-sealing. If the work is done at a repair shop you might consider error on the side of caution and replace the timing cover entirely.
4) M157 AMG Coolant Hose Leaks
Coming from the BMW world we are very familiar with coolant hose leaks, and well, all coolant leaks in general. With age and mileage the M157 coolant hoses are prone to splitting, cracking, or simply popping loose. Generally coolant hoses are easy repairs and do not warrant much concern. However, beware if the leak is bad enough to cause rapid coolant loss.
Over-heating is seriously detrimental to an engine and may cause the need for expensive repairs. Once the engine is out of coolant things will get hot very quickly. If the coolant loss is rapid consider towing the car home or to the repair shops. In the case of less severe leaks you can simply top up on coolant to get it somewhere to inspect and repair.
Coolant Hose Leak Symptoms
The symptoms for a coolant leak are obvious in most cases. Minor coolant hose leaks will likely result in nothing more than a few drops of coolant under the car and an eventual low coolant warning. Drastic M157 coolant leaks will result in more obvious symptoms, such as:
- Coolant under engine area
- Rapid overheating
- Low coolant light
Again, coolant hose leaks are generally not a repair to worry about. Though, it’s important to pay attention to the rate of the leak. The M157 will overheat within minutes of losing too much coolant.
Coolant Hose Replacement
Depending on which hose(s) is leaking specifically these are generally fairly simple, inexpensive repairs. Most coolant hoses are under $75 and relatively simple DIY repairs. As the hoses are inexpensive, it may make sense to preventatively replace any hoses in the general area. Especially as the M157 ages and miles accumulate.
Mercedes M157 Problems & Reliability Summary
As we stated early, the M157 is a reliable engine overall. Don’t expect Honda-like reliability and cost of repairs, but it’s certainly more reliable than many high performance engines out there. A few common issues include the timing chain, spark plugs, valve timing cover, and coolant hoses. Of course, this is not an exhaustive list of things that can go wrong with the M157.
As the engine continues to age expect more “common problems” to pop up. That is simply the nature of high performance engines as they age. Nonetheless, the Mercedes M157 AMG engine is one heck of an engine. With a whopping 500+hp and respectable reliability record it’s hard to go wrong with this engine.