The Mercedes OM606 diesel engine. For a lot of diesel guys and gals here in the states, this name might not ring a bell. After all, we’re used to talking about Cummins, Powerstroke, and Duramax engines. Diesel engines in cars aren’t nearly as popular here as they are nearly anywhere else in the developed world.
Although you might not know all that much about this engine, it’s regarded as one of the best automotive diesel engines ever, and that’s a bold statement considering just how many great engines are out there, but today we’re going to dive in and find out exactly what makes the Mercedes OM606 diesel engine so special.
The History of the OM606 Diesel
The history of the OM606 engine began in the late 1980s when Mercedes-Benz began developing a new line of diesel engines to replace their aging OM617 and OM603 diesel engines. While those engines are decent in their own right, they were simply aging out, and something newer was needed.
Add to screen (OM actually stands for Oel Motor, which quite literally means an engine that can run on oil.)
With the new OM606, the goal was pretty simple: take what they had done with their other diesel engines and simply improve upon it. They wanted to develop an engine that was more powerful, efficient, and environmentally friendly than its predecessors, and to do this. They needed to bring some modern innovations to the platform.
And if we were to look at this chronologically, the OM606 is the successor to the OM603, which it shares a fair bit with.
It took Mercedes a few years, but eventually, the OM606 was finally introduced in 1993. And with it came a number of advanced features that separated it from the pack. Before we look at those features and what makes it so special, though, we should briefly cover some of the basic specs, so we’re all on the same page about what the OM606 is.
Basic Specifications and Info
Just getting straight to the point, the Mercedes OM606 diesel engine is an inline-six engine with a total displacement of 3.0 liters. That’s achieved through a bore and stroke of 87mm by 84mm, respectively. The compression varies depending if you’re looking at an earlier naturally aspirated version or a later turbocharged version, at 25:1 for the N/A models and 22:1 for the turbo models.
The block is constructed from cast iron, just like the OM603 before it, and the cylinder head is made from cast aluminum.
A big thing that separates OM606 from the OM603 is the change from a single overhead camshaft to dual overhead cams. With that design change comes four valves per cylinder, resulting in a surprisingly good cylinder head for a 90s diesel engine, at least in theory.
Again because of the fact that there are turbo and non-turbo variants, the power ranges from 134hp up to 174hp, which is really not all that much considering one of those engines has forced induction, but power isn’t everything, and certainly doesn’t tell the full story of what makes the engine special.
- Displacement: 3.0 liters (2996 cc)
- Configuration: Inline-six
- Valvetrain: DOHC, four valves per cylinder
- Horsepower: 177 hp at 4400 RPM
- Torque: 330 lb-ft at 1800-3000 RPM
- Bore x stroke: 87 mm x 84 mm
- Compression ratio: 22.0:1
- Engine weight: 496 lbs
What Makes it Interesting
Okay, enough with the basic specs and info. Let’s get into what makes this engine so interesting and so special. And starting it off, I think it’s worth mentioning the weight of this engine because it’s absolutely wild as compared to the majority of diesel engines, but especially American-made engines.
Coming in at 463 lbs dry, the OM606 is extremely lightweight for a diesel engine. Seeing as how this engine is often referred to as the European 2JZ or diesel 2JZ, I think it’s fair to compare it to the Toyota 2JZ in terms of weight.
And for those who don’t know already know, the Toyota 2JZ is a legendary gas engine from the 90s that happens to also be a 3.0L inline-six like the OM606. It makes decent power in stock form, but it’s really praised for its ability to make power with aftermarket parts. Regardless of that, both the OM606 and the 2JZ are 3.0L inline-six engines. However, the 2JZ weighs more than the OM606.
As a quick side note, I think a big part of the reason this engine ended up with that diesel 2JZ nickname is because of how incredible it sounds, especially as compared to pretty much any other diesel engine. It sounds like a true inline-six performance engine.
Typically diesel engines are significantly heavier than gas engines, so this definitely helps separate the OM606 from the pack. Another engine worth referencing for weight is the Cummins 4BT, which is a popular little 3.9L four-cylinder diesel engine that you can find lying around all over the world, but especially here in the states, and that engine comes in over 300lbs heavier than the OM606 while also making less horsepower, albeit, it makes more torque.
Something that is comparable in terms of weight would be an engine like a new 3.0L LM2 Duramax, which weighs nearly the same amount but makes quite a bit more power.
But, the fact that you have to jump up 20+ years to find a 3.0L diesel engine with comparable weight is pretty insane and speaks volumes about the OM606.
The low weight really makes the OM606 a much better alternative for swapping into a project car as compared to nearly any other diesel at this size.
In terms of the OEM applications for this engine, Mercedes actually used it in a handful of different vehicles, including the E-Class, S-Class, and, not too surprisingly, the G-Wagon.
Expensive and Hard to Find
But, that brings us to the glaring issue with this engine, at least for those of us here in the states, which is that getting your hands on this engine is quite difficult and very expensive. And that’s simply just because diesel cars aren’t very popular in the US, meaning finding a good running example of this engine is fairly difficult.
That leaves most enthusiasts who desire to use this engine stuck with being forced to import it from Europe, where diesel car engines and particularly the OM606 engine, is much easier to find.
Injection System
But even that brings me to my next point, which is that with this engine spanning through the 90s and being used in various applications, not all OM606s are built the same. We already mentioned that this engine was available new in both naturally aspirated and turbocharged forms, but another important variable to consider is the injection pump.
Depending on the year and model that you’re looking at, the OM606 could be had with either a mechanical injection pump or an electronic injection pump.
In the early days, the electronic injection pump models weren’t tuner friendly at all, which made it quite difficult to tune them and turn up the fueling.
Luckily, that’s not quite the case anymore, but that still leaves the mechanical injection pump as the preferred variant for many enthusiasts.
And funny enough, this is actually another area of this engine where you see ridiculously impressive weight savings, with the OM606 injection pump coming in about 1/3rd the weight of something like the Bosch P7100 found on the 4BT. That’s far from an apples-to-apples comparison, but still something worth highlighting regardless.
With either the mechanical or electronic injection pump, a good way to pump up horsepower is to add something like a Holset HX35 or even HX40.
That is, of course, assuming we’re talking about a turbocharged OM606, as slapping a big turbocharger on an N/A OM606 with likely result in a connecting rod entering the atmosphere.
And you might think I’m kidding when I say that, but the difference in the pistons and connecting rods between the turbo and N/A models is pretty stark.
https://www.team-bhp.com/news/upgrading-my-1995-mercedes-w124-diesel-produce-500-bhp
I want to give a shoutout to team-bhp.com for the images you’re about to see, which help to clearly illustrate the point I’m trying to make. In this image here, you can see the bottom side of a turbo OM606 piston on the left and an N/A piston on the right. They share the same total bore, but as you can see, one of them is significantly larger than the other.
You can see the same thing here, too, with the connecting rods, where once again, the turbo model is much beefier. So much so, that on a stock bottom end, it’s fairly easy to push an OM606 to upwards of 500hp without major changes to the rotating assembly.
Summary
So, that’s the legend of the Mercedes OM606 diesel engine. It’s an absolute beast, surprisingly reliable for a german product, capable of making big power on a stock bottom end, and probably the best-sounding road-going diesel engine ever.
And I just want to say really quickly, there is loads of conflicting info online for this engine which makes it really hard to figure out what’s incorrect and what isn’t. So please, if there is anything I missed or anything you want to add, be sure to drop it in the comments below.
I want to compile the absolutely perfect guide to this engine over on the Dust Runners website, so any accurate input is massively appreciated.
As a quick side note, I’d love to see your comments discussing if this is the best german diesel engine ever of if something else holds that crown.