V8 and diesel torque, sign us up! These cars feel like you’re driving a train, literally. Ever since I’ve tried one in a W211 E-Class I can’t stop thinking about. But trust us, owning one of these is no joke. Eventhough you can buy it for cheap, it certainly isn’t cheap to maintain.
Doing your own homework when it comes to purchasing a car with such a specific engine is always a good idea. You just don’t want to end up in a money pit full of problems and this is why we are here to help you out.
First, we are going to cover the basic specs of these engines and then we are going to list the Mercedes OM628 and OM629 engine problems and also learn in which models these engines were included, so without further ado, let’s dive into the article.
Basic Mercedes OM628 & OM629 Specs
When it comes to the specs of these engines, it is worth noting that these are two diesel V8s produced by Mercedes Benz.
The OM628 is the earlier variant produced between 1999 and 2005, while the OM629 is the later variant produced between 2005 and 2013.
The OM629 features a lot of improvements compared to its predecessor, such as common-rail diesel injection, as well as a higher boost from the turbos. Thus, producing more power compared to the original engine.
Here are the specs of the OM628 Engine:
- Configuration: V8
- Displacement: 4.0L
- Cylinder Bore: 86 mm
- Cylinder Stroke: 86 mm
- Engine Block Material: Aluminum alloy
- Cylinder Head Material: Aluminum alloy
- Cylinder Head Design: DOHC, 4 valves per cylinder
- Compression Ratio: 18.5:1
- Turbocharger: Twin-turbo
- Fuel Injection: Common rail
- Fuel Type: Diesel
- Power Output: 247 to 256 hp (184 to 191 kW)
- Torque Output: 560 N-m (413 lb-ft)
Here are the specs of the OM629 Engine:
- Configuration: V8
- Displacement: 4.0L
- Cylinder Bore: 86 mm
- Cylinder Stroke: 86 mm
- Engine Block Material: Aluminum alloy
- Cylinder Head Material: Aluminum alloy
- Cylinder Head Design: DOHC, 4 valves per cylinder
- Compression Ratio: 17.0:1
- Turbocharger: Twin-turbo
- Fuel Injection: Common rail
- Fuel Type: Diesel
- Power Output: 302 to 315 hp (225 to 235 kW)
- Torque Output: 700 – 730 N-m (516 – 538 lb-ft)
Common Mercedes OM628 And OM629 Engine Problems
Common problems with the OM629 and OM629 engines include:
- Leaky Injectors
- High-Pressure Fuel Pump Failures
- EGR Failures
- Turbocharger Failures
- Prolonged Overheating Leads To Cylinder Bore Scuffing
- Cylinder Heads Crack
- Glow Plug Failures
- Timing Chain Failures
- DPF & Intake Manifold Clog Up With Carbon
We covered the common problems, now let’s move on and learn more about how and when they appear, along with the symptoms they produce. And also, how expensive it is to sort these problems out.
Leaky Injectors
One of the biggest issues with these engines is the situation with the injectors. They can clog up, or in the worst case, they can leak diesel.
Having leaky injectors is not something that you want, because first, they are very expensive to get replaced and also, they are a pain to get removed.
If the vehicle has a lot of miles, they are stuck there for good and without special tooling, good luck removing them.
Nevertheless, whenever these injectors fail, they start to produce symptoms, which will result in worse fuel economy, more emissions, an unburnt diesel smell, as well as hot start problems.
Unfortunately, on higher mileage engines, these problems are very common and they often trouble a lot of owners. Trust me, I’ve been through this on my OM642 V6 diesel engine.
This is why if you plan to purchase a car with one of these engines, it is worth checking the condition of the injectors and seeing if they are creating some trouble codes on the diagnostics tool.
High-Pressure Fuel Pump Failures
The high-pressure fuel pump can also fail and cause issues in these cars. These cars are using common-rail injection.
This type of injection requires a high-pressure fuel pump and this fuel pump is installed on top of the engine.
These high-pressure fuel pumps can fail internally and leak. Whenever there are major leaks in the engine, it can lead to an engine fire.
This is why it is important to detect these problems before they exacerbate and cause some irreparable damage. Common symptoms are the check engine light, visible leaks, and poor engine performance.
EGR Failures
EGR failures are also common on these engines as well. These EGR failures are normal diesel issues.
Diesel as a fuel does not burn very cleanly and creates soot that is collected inside the EGR valve. This soot will prevent the EGR from opening and closing correctly.
The only way around this problem is to clean the EGR manually. But we often recommend replacing the whole unit since this EGR will not be good as it was before.
Turbocharger Failures
Turbocharger failures are also common on these engines as well. Turbochargers as you know are the components that create boost and help your engine make more power.
There are two turbos on this engine and at 150,000 to 200,000 km, they will start to develop strange noises such as whistling and sometimes oil leaks.
This means that the turbo is due to be refurbished. Whenever this happens, you will have a loss of power, check engine light, and oil leaks coming from the turbos. Refurbishing can be expensive, so beware of this issue that is present on these higher mileage cars.
Prolonged Overheating Leads To Cylinder Bore Scuffing
Another very common problem with this engine is the damage to the cylinder bore under prolonged overheating. Why is this the case?
This is the case because these were one of the first engines made out of aluminum alloy. Aluminum is a soft metal that is not like cast iron.
So, in other words, the block does not tolerate a lot of heat. The more heat, the worse the scuffing will get and there can also be cracks developing on the block.
That’s why you should always monitor the temperatures and make sure that the temperatures are on the recommended level. This isn’t the only Mercedes engine to experience this problem, I’ve noted it on the M157 petrol engine as well.
Cylinder Heads Crack
Another common issue with these engines is the cylinder head developing cracks. This issue is common on many Mercedes Benz engines from this era.
What happens is that there are cracks that develop where the glow plugs are located. And this crack goes from the glow plug to the valve.
A solution when it comes to this problem is to repair the cylinder head and resurface it. Or the more recommended route is to go for a used cylinder head that does not have cracks.
Symptoms when it comes to this problem can be the check engine light, low compression, and poor engine work.
Glow Plug Failures
Glow plugs can also fail often on these engines. Glow plug failures are common on diesel engines. Especially at higher miles.
The only way around this problem is to replace them with new ones. Luckily, they are not very expensive to replace. But removing them can be an issue.
Timing Chain Failures
Timing chains are notorious for failing on these engines. Many people think that these timing chains will last for a lifetime. Which is not actually the case.
Whenever the chain reaches 150,000 to 200,000 km, the chain will stretch and start to rattle. In this situation, the only way around this problem is to replace the chain. This can be a very pricey service since there is a lot of work involved.
DPF & Intake Manifold Clog Up With Carbon
These engines come with DPF, which is the diesel particulate filter. This filter is an emissions device designed to collect the soot and reduce NOx particles.
If you drive too often in the city, the DPF will not regenerate and clean this soot. A mistake that a lot of people make and they end up with a clogged DPF.
That’s why we recommend driving frequently on the highway at higher RPMs to remove this soot from the DPF as well as from the intake manifold, which is another component that can clog up with soot.
Which Models Have The OM628 & OM629 Engines?
Now let’s take a look at which models have the OM628 engine.
184 kW version
- 1999 – 2003 Mercedes Benz W220 S400 CDI
- 2001 – 2005 Mercedes Benz W163 ML400 CDI
- 2001 – 2005 Mercedes Benz W463 G400 CDI
191 kW version
- 2003 – 2005 Mercedes Benz W211 E400 CDI
- 2003 – 2005 Mercedes Benz W220 S400 CDI
Now let’s take a look at which models have the OM629 engine.
225 kW version
- 2006 – 2009 Mercedes Benz X164 GL420 CDI
- 2007 – 2009 Mercedes Benz W164 ML420 CDI
- 2009 – 2010 Mercedes Benz X164 GL450 CDI
- 2009 – 2010 Mercedes Benz W164 ML450 CDI
231 kW
- 2005 – 2009 Mercedes Benz W211 E420 CDI
235 kW
- 2006 – 2009 Mercedes Benz W221 S420 CDI
- 2009 – 2010 Mercedes Benz W221 S450 CDI
FAQ
What Are The Common Mercedes OM628 and OM629 Engine Problems?
Problems with this engine include leaky injectors, high fuel pressure pump failure, glow plug failure, and turbocharger failure. Carbon deposits on EGR, DPF, and intake manifold. As well as cylinder head cracking.
Are The Mercedes OM628 and OM629 Reliable?
The OM629 is a more reliable engine compared to the OM628. Most of the issues were patched on the newer engine. But the downside is that this engine was not available in the US. So, the only option, if you live in America, is the OM628 engine.
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