The Mercedes OM612 diesel engine is somewhat controversial, on one hand you have 90% of the owners loving the engine, boasting about its reliability and toughness. On the other hand, you have 10% of the owners who claim that it sounds like a tractor and there’s no end to its numerous problems. Let’s find out who’s right!
The 2.7 L / 3.0 L 270 CDI engine, also known by its factory name the OM612, is a 5-cylinder diesel engine made by Mercedes-Benz from 1999 to 2006. Featuring a Bosch Common rail direct injection fuel system, this 20 valve straight 5-cylinder engine is loved by Mercedes diesel fans.
Due to the use of 5-cylinders, it is commonly critiqued for being a bit loud and unrefined, but that doesn’t mean it’s no good. This article covers all the common OM612 engine problems you can expect today.
Common Mercedes OM612 (270 CDI) Engine Problems
The issues that we list here are based on our experience, web research and NHTSA’s owners complaints. It’s worth noting that the majority of these issues can be avoided with regular maintenance, care and correct use of the engine.
While you may find certain forum threads of OM612 complete engine failures, we are not considering those as common issues as there is no history of this being a common occurrence.
Intake manifold / swirl flap problems
Just like the OM646 engine or the V6 OM642 engine, the OM612 experiences problems with the swirl flaps inside the intake manifold. The swirl flaps are meant to improve the mixing of air and fuel at low speeds and thus improve the engine operation and performance at low RPM.
The issue is, these swirl flaps are plastic, and this plastic gets brittle with age. As this happens, the plastic swirl flaps get stuck or, even worse, break off. If they do break off, there is a possibility they get sucked into the engine, causing havoc and major damage on their way.
Another problem is carbon and oil deposits. Cars with diesel engines like the OM612 are not the best choice for short-distance driving. Short journeys can quickly coke up these engines, which leads to carbon build up in the intake manifold and all over these plastic swirl flaps. The carbon deposits can block the movement of the swirl flaps. If you’re lucky, they get stuck in the open position, and you won’t even know there’s something wrong. That’s usually not the case.
“Black Death” CDI fuel injector seal failures
The internet has gloriously named the infamous CDI fuel injector issue as “Black Death”. Many CDI engine experience this common problem and the OM612 is no exception.
Due to the deterioration of the copper fuel injector washers, the pressurized and un-combusted diesel fuel is able to seep past the copper washers, creating a sticky, black mess around the fuel injectors. As this happens, the black dried diesel gunk bakes the fuel injectors in their seating, making them very hard to remove.
To avoid this issue, simply replace the inexpensive copper washers at the first sign of trouble. Simple!
EGR valve problems and EGR oil leaking
There are two different EGR valve designs on the OM612 engine, the pre-2004 which is air cooled and the post 2004 design which is water cooled. Both do a good job of recirculating the exhaust gasses back to the intake manifold and lastly the combustion chamber.
The most common problem with EGR valves on the OM612 engine is leaking. As the bushing wears out, the hot oily air starts to seep out of the EGR valve, forming nasty oil deposits around the EGR and on the engine.
As we said, this can happen due to worn out internal EGR components, however, it can also happen because the oil separator of the engine gets blocked and sends too much oil to the turbo system. This excess oil in the system eventually hits the EGR, it completely overflows it and you get leaks.
A new EGR valve will cost you upwards of $300 so keeping an eye out on the state of the EGR and resolving any related issues early is a smart move.
Mass Air Flow (MAF) sensor malfunctions
Finding a faulty MAF sensor on the OM612 engine is no surprise. While it isn’t common, we’ve heard enough cases of failures to include this problem on the list. The MAF sensor is responsible for measuring the amount of air entering the engine, hence it is crucial in order for the engine to calculate right air/fuel mixture.
A faulty MAF sensor on the OM612 engine will lead to rough starting, erratic idling behaviour, engine stalling after starting, overall erratic engine behaviour and even black exhaust notes due to rich air/fuel mixture.
OM612 oil leaks
Oil leaks are best fixed as they occur. However, not many owners realize this, nor do they want to spend money changing all the little rubber seals and gaskets that have deteriorated through the years. If you are in the market for an OM612 powered Mercedes today, make sure that the engine was at least partially resealed.
If not, get ready for leaks galore. Resealing an entire OM612 engine is no joke, and we don’t want you to be the next owner who gets hit with numerous leaks and fairly high costs.
OM612 engine harness problems
An engine harness is a set of wires, connectors, and cables that connect all the electronic components of the engine with the car’s ECU and other electronic components. A number of OM612 owners experience problems with the engine harness. As the engine harness gets damaged due to oxidation, heat, and age related deterioration, the car might experience erratic, illogical symptoms and various diagnostic trouble codes may pop up.
Replacing the engine harness is neither simple, nor is it cheap. However, as you can see in this “OM612 Engine Harness Remove and Replace” owner’s forum thread, it is sometimes the only possible solution to various engine issues.
High mileage problems
The majority of these cars have covered many miles by now. Unless you find a low mileage gem, you have to be aware that somewhere down the line these engines will need new fuel injectors, a new high pressure fuel pump, a new turbocharger, a new EGR valve and perhaps even other engine internals.
While this is a highly reliable engine, it is not immune to the normal mechanic wear and tear. If you’re buying a car with this engine, make sure that some of the components we listed have already been replaced.
Which Mercedes Cars Have the OM612 Engine?
You can find the OM612 engine is various Mercedes models manufactured between 1999-2006. Here is a full breakdown.
- 125 kW / 170 hp version – W210 E-Class, W203 C-Class, W163 ML and W209 CLK
- 170 kW / 231 hp version – W203 C30 CDI AMG C-Class
- 115 kW / 156 hp version – W903 Mercedes Sprinter, W463 G-Class
- 120 kW / 165 hp version – W210 E-Class, 2003-2005 Jeep Grand Cherokee (not a mistake)
What are some common Mercedes OM612 engine problems?
If you’re in a rush, here’s a quick overview of the OM612 engine problems:
- Intake manifold swirl flaps problems
- Fuel injector washer leaks (”CDI Black Death”)
- EGR valve problems
- Mass Air Flow sensor malfunctions
- Engine oil leaks
- Engine harness damage
How would we describe the OM612 engine reliability?
The OM612 engine is without a doubt one of the great Mercedes diesel engines. These engines have no issues reaching upwards of 300,000 miles (ca. 482,803 km) or more if maintained properly. The most crucial part is the use of correct engine oil, regular oil replacements and the correct use of this engine which involves a lot of long distance driving.
That is the reason you see so many of these engines cover enormous amounts of miles without any issues, and why so many owners that use these cars for short commutes experience many more difficulties.
What was the commercial name of the OM612 engine?
The OM612 5-cylinder diesel engine carried the 270 CDI badge. Any Mercedes with the 270 CDI badge on the back features this 2.7 L diesel engine.