Mercedes-Benz M112 engine problems: For those of us living in Europe, the M112 engine was always thought to be a fuel consuming lump of an engine that everyone avoided at all costs. This was mainly due to our diesel loving mentality, and people just could not cope with the fuel consumption of a V6 petrol engine.
The M112 engine was the first V6 to be made by Mercedes-Benz, and they were on the money right from the get-go. With an aluminium engine block and head material, this 2.4 L to 3.7 L was built to last. Featuring 3 valves per cylinder and 2 spark plugs per cylinder, there was nothing particularly prone to failure in this engine, not even the IHI Twin-screw type supercharger fitted to the later M112 E32 ML 32 AMG engine.
This article will reveal all the common M112 engine problems and concerns.
Common Mercedes M112 Engine Problems
Before we dive deeper, it’s important to note that the majority of these M112 engine problems can be prevented with regular maintenance and care.
Disintegrating crankshaft pulley / Harmonic balancer problems
A number of owners of the M112 engine, especially those with 1998-2000 model year vehicles, were faced with a failing crankshaft pulley or harmonic balancer as it is also called. The harmonic balancer pulley drives the accessory belts on this engine and at the same time minimize engine vibrations by implementing a rubber piece between the pulley outer ring and the centre of the crankshaft pulley.
This rubber element is the culprit behind these failures. As is normal for all rubber components, heat and time take their toll. As the rubber on the crankshaft pulley starts deteriorating, many owners felt much more engine vibrations and those careless enough even experienced complete failure, which can lead to major engine damage.
The problem was so bad, there was even a recall triggered on the American market. This issue was later resolved with an improved design and materials, so it should not be an issue today. In any case, it was and is a fairly simple repair, so it’s not a major concern.
Crankshaft position sensor failures
Failures of the crankshaft position sensors were common with these engines. The sensor is located at the back of the engine, and it’s vital for the correct operation of the engine as it monitors the speed of the crankshaft, calculates the engine’s RPM and more.
Despite being a small and inexpensive sensor, it can leave you stranded by the side of the road as it fails. A key thing to note here is that if the sensor starts to malfunction, it will cause your engine to stall, but then start normally again as it cools off. This is a typical symptom of a failing crankshaft position sensor.
Replacing the sensor costs less than $100, so we recommend you do it as soon as there are first signs of trouble. Certain chassis, like the W211 E-Class with the M112 engine, make replacing this sensor a real problem as there is very little access at the back of the engine where the sensor is located.
This is one of the most common M112 engine problems, many owners choose to replace this sensor preventively just to avoid getting stranded.
M112 engine oil mixing with engine coolant
Those of you that know, know. Seeing your coolant disappearing and finding out that it’s mixing is usually a sign of a catastrophe. By now, you’re probably thinking we’re going to say that this engine is suffering from head gasket failure. Luckily you’re wrong.
The cause for this are just two O-ring seals. Although they are a pain to replace, it’s good news that your engine is not toast if this happens.
The O-rings at fault are located between the engine block (V-section) and the timing gear housing. As heat accumulates in the block’s water channels, the cooling system side is undoubtedly a high pressure area. As oil flows back into the oil sump, the timing gears are on a low pressure area of oil in the lubrication system. Because of the high pressure on the cooling side, the o-rings become brittle and allow the engine oil to mix with the coolant.
To learn more, consult this amazing video on Youtube.
The majority of these engines are now at least 20 years old. If you’re buying a car with this engine, you should be aware that there could be a number of oil leaks due to deteriorated gaskets, o-ring and seals. Here are some areas you should pay attention to:
- Cam cover
- Oil heat exchanger
- Oil separator
- Camshaft plugs
- Oil pan leaks
- Valve cover leaks
- Oil filter housing and cooler gaskets
Engine breather / crankcase ventilation hose blockages
To prevent excessive pressure in the engine, all modern engines feature some sort of crankcase ventilation breather systems, including the M112. By doing that, the engine is allowed to create a tighter seal between the piston rings and cylinder walls. This leads to less oil consumption, more power, and it expands the engine lifespan.
Keeping the engine breather hoses in pristine condition should be a priority. The M112 engine is known to have blockages in these hoses.
Coil pack problems
Due to oxidation on the coil pack contacts, the M112 engine is known to experience coil pack malfunctions and failures. There are 6 coil packs, each containing 2 spark plugs. As the coil packs malfunction, the engine starts misfiring and running roughly.
M112 intercooler problems
Making sure that the engine is running cool is essential to keep it running strong and healthy. Both the M112 and the M113 V8 engines are known to have intercooler pump failures, which can lead to overheating.
Damaged valve stem seals leading to oil consumption
This is not one of the common M122 engine problems, however, we have seen cases of damaged valve stem seals causing serious oil consumption problems. This is something you cannot check when buying these engines, but it’s good to keep in mind if you ever run into oil consumption issues with this engine.
Blocked EGR valve causing rough idle
Rough idling can be caused by several issues, including a blocked or malfunctioning EGR valve. This isn’t a common issue, but it is known to happen.
Due to a bad return valve in the main fuel pump and consequently low sub 4 bar fuel pressure, the V6 M112 engine is known to become sluggish from the start and at hard accelerations. This is a common issue at higher mileage, and it’s an easy fix.
Sensitive fuel injectors
The M112’s fuel injectors are bullet-proof, and we’ve seen these engines past the 300,000-mile mark with original fuel injectors. They are however extremely sensitive to poor quality, dirty fuel. This used to be a bigger issue in the late 90s when these engines rolled out, however, it can happen today that the mesh screen fitted to the fuel injectors gets dirty and blocks the fuel flow.
These mesh screens can be replaced and by doing that, most owners resolved their fuel injector issues. Avoid dodgy, potentially dirty fuel!
Best Variant and Model Year of the M112 Engine
There’s many M112 variants to choose from, from the smallest E24 2.4L version to the supercharged E32 ML 3.2L and the E37 3.7L version. Based on our experience, none of the variants experience serious issues. However, there’s no doubt in our minds that the most long-term reliable will be the naturally aspirated variants that run with lower compression.
In terms of model years, we recommend avoiding the pre-2001 model year engines as they did suffer from certain initial issues that were later resolved, the harmonic balancer issue being one of them.
Which Mercedes Cars Have the M112 Engine?
From 1998 to 2008 a number of Mercedes cars were blessed with the M112 engine, here’s the full breakdown:
|Engine version||Basic specifications||Cars with this engine|
|M112 E24||2.4 L |
125 kW – 170 hp
|1996–2000 W202 C-Class 240 |
1998–2000 W210 E-Class 240
|M112 E26||2.6 L |
125 kW – 170 hp
|2000–2005 W203 C-Class 240 |
2000–2002 W210 E-Class 240
2003–2005 W211 E-Class 240
2002–2005 C209 CLK-Class 240
|M112 E28||2.8 L |
150 kW – 204 hp
|1998–2000 W202 C-Class 280 |
1998–2006 W220 S-Class 280
1998–2002 W210 E-Class 280
|M112 E32||3.2 L |
215 – 224 hp (depending on the version)
|2000–2005 C-Class 320 |
1998–2005 E-Class 320
1997–2006 G-Class 320
1998–2002 S-Class 320
1998–2003 ML-Class 320
2000–2003 SLK-Class 320
1998–2005 CLK-Class 320
2003–2015 Viano 3.0/Vito 119
|M112 E32 ML||3.2 L |
260 kW – 349 hp
|2001–2003 C-Class 32 AMG |
2001–2003 SLK-Class 32 AMG
2002 A-Class 32K AMG
|M112 E37||3.7 L |
235 – 245 hp
|2003–2005 ML-Class 350 |
2003–2006 S-Class 350
2003–2006 SL-Class 350
2004–2008 V-Class 350
Conclusion – M112 engine reliability
Just like it’s big V8 brother, the M113, the M112 engine is one of the greatest Mercedes-Benz engines ever produced. Apart from to-be-expected problems like oil leaks after 10+ years, the engine is essentially fault free or at least free from any serious problems that would cause premature failures. One thing is for sure, this V6 Gasoline engine is definitely more reliable than his V6 diesel counterpart, the OM642 engine.
With regular maintenance and care, the M112 engine should have no difficulties reaching the 200,000-mile mark and beyond. We’ve seen cars with these engines running smoothly even beyond the 300,000-mile mark. These machines need a loving owner and they’ll run essentially forever.
If you’re in the market for a Mercedes with the V6 M112 engine today, make sure that it has an impeccable service history. We recommend getting the car inspected and taking advantage of the test drive.
Mercedes M112 vs M113, which is better?
In terms of reliability, both engines are incredibly reliable. However, the maintenance costs and the gas station bill will be slightly bigger with the bigger V8 M113 engine. Don’t forget about higher registration and insurance costs as well.
If we had to pick one, we would go for the M113 engine simply because we love V8 engines, the V6 M112 engine however is just as good.
Is there a W211 E-Class with the M112 engine?
Yes, the W211 E-Class Mercedes did feature the amazing M112 engine in the 2003–2005 W211 E-Class 240 and 320.