My wife totaled my W211 V6 and we need another car. I am considering Diesel due to it's MPG and my impression that it runs 200+kmiles - if it runs that long then it must be reliable!!

I was considering buying W211 with OM642. I reached my car shop for opinion and the owner warned me that MB diesel is total junk. It breaks much more often than gasoline engine and I should remove this word "diesel" from my brain if I don't want to commit myself to visit the car shop every so often for repair.

I am sure someone in diesel forum would tell me a totally different, yet true story that his MB diesel is rock solid.

Is there any published data that compares the long-term reliability of MB diesel vs gasoline engine, preferably M272 vs OM642?

 

I own a w211 with the om642 diesel. I can confirm your mechanics opinion. The om642 has a couple of common and expensive repairs, most notably the oil cooler leak and the swirl motor. I opted for the diesel because when I was car shopping five years ago all the petrol v6 cars were having the balance shaft problems, which is also quite expensive to repair. Fuel economy on the om642 is not all that great. The 2012+ direct injection gasoline cars will nearly match it while having 100 additional horsepower.

The new 4 cylinder diesel might be better, but I don't think we know yet. The w211 is my 4th MB diesel and my last one as well. Diesel just doesn't make sense in the US any longer - the engines are too complex and hence too unreliable. Newer diesels all use DEF and hence don't carry a spare tire, which is a deal breaker for me.

 

Ah! thank you!! I found more background from what you said, and it looks both are true. It looks I would be better off getting a 2009 W211 with M272

Quoted Wikipedia "Mercedes-Benz M272":

M272 engines that were sold between 2004[1][2] and 2008 with engine serial numbers below 2729..30 468993 often show early wear of the balance shaft gears, requiring extensive repairs at a retail cost of over $4000.[3][4] These complaints led to a class action lawsuit against Mercedes-Benz (Greg Suddreth and Paul Dunton v. Mercedes-Benz USA, LLC), which alleged the M272 engines are equipped with defective balance shafts gears which "wear out prematurely, excessively and without warning, purportedly causing the vehicles to malfunction, the check engine light to illuminate and the vehicle to misfire and/or stop driving." [5] The suit further alleged that Mercedes knew of this problem, sending out repair bulletins on how to address this issue and ultimately changing the balance shaft gears to avoid this problem. This suit was ultimately dismissed with the judge agreeing with Mercedes that because the gears fail at 60 -80K miles and outside of the warranty period, Mercedes is not legally responsible for these problems.[6]
However, a second class action lawsuit was filed in October 2012 in Northern California,[7] covering Mercedes-Benz models manufactured between 2005 and 2007. A preliminary settlement was reached on April 8, 2015,[8] which would see owners compensated for up to 70% of the cost of the repair. The settlement terms are expected to be ratified in August 2015.

Quoted from Wikipedia "Mercedes-Benz OM642":


Due to the inordinate number of pre-2010 OM642 engines needing repair due to heat-related seal degradation causing oil cooler leaks, Mercedes reformulated the seals from an orange color rubber to a purple color Viton seal now used in all 2010 and later engines. There is a Mercedes Technical Service Bulletin that states that the leak can be attributed to an improperly installed seal.[5] This engine also has an inherent design flaw with the TWC temperature sensor (part no. A005 153 40 28) and the part in the electronic parts catalog is now specifying part no. A007 153 74 28; there is no recall on this service item yet. A check engine light may present with the OBD-2 diagnostic code P2031 upon failure of this sensor.[6]
Oil specification MB 229.51 or MB 228.31 is recommended, for the bluetec engine in the G w463, GL x164 and Ml w164 the oilspec. is 229.52 class.[7]
In addition to the oil cooler seals; this engine can also have an issue with the design of the positive crankcase ventilation system. The crankcase ventilation system vents to the inlet of the turbo. The issue is that the air vented from the crankcase contains too much oil to easily pass through the swirl motor valves downstream of the turbo. Once this oil and sludge begin to accumulate, the valve becomes inoperative and blows a fuse that controls many other sensors required to properly operate the engine and emission system. This will immediately place the vehicle into limp home mode and limit the rpm to 3000. It also causes a check engine light and numerous OBDII Codes. Mercedes Benz has previously recognized this feature of the vehicle and has stated that this engine feature, the accumulation of oil at the turbo inlet, is "normal". In a Technical Service Bulletin they issued in 2008 they state: "Engine oil venting occurs on the right hand side of the engine air intake duct. For this reason there is always some oil in the engine air intake duct, see (Figure 3). This is no justification for replacing the turbocharger. Turbochargers replaced for this reason will not be covered by warranty."[8] While a slight amount of oil may be normal and acceptable, sufficient quantities and accumulation will indeed lead to other failures as identified above.

 

Chances are if you get a used OM642 with the oil cooler seal leak, it has already been repaired with the new seal. The crank case vent into the turbo inlet, has only been an intermittent issue, but you can resolve this with a bypass or catch can. The swirl valve can be disabled with an EGR software delete.

An additional issue is the glow plug controller, which can be considered a consumable item, and can be replaced with an aftermarket one that will last indefinitely - this is a quick DIY.

All-in-all, the OM642s are quite reliable.

 

I have had 2 diesels over 21 years. The earlier one only had one electronic item associated with it , the electric fuel shut off valve. The 8 year old MB 4 cyl OM 646 diesel I now have thankfully has no DPF but has a massive amount of electronic controls It is running well. I bought it partly because it was a country car & we did long trips.Now that we live in a built up area & do short trips I am certain that I would not by another diesel. These DPFs need a good run to do they regeneration.

 

I don't think I would own any modern diesel that was going to stay stock based in software or hardware. My W211 OM648 has been VERY reliable but stock programming was deleted along with many other parts about 60,000 miles ago. I also have an OM642 powered Sprinter truck, it has a 120,000 mile warranty. It is 100% stock due to this fact and being a working truck. It has been terrible honestly in terms of trouble free reliability and I will not buy another diesel truck from the modern era to replace it. In last month at just under 80k miles both Nox sensors and SCR catalyzer replaced by MB and that even has not fixed all issues, sure to be back at dealer soon enough anyway since they refuse to replace more than glow plug at a time, three separate glow plug jobs in last 18 months. I'm a diesel nut btw so it's not really an implied bias or anything, just a commentary on the more grim realities of most modern diesel cars/trucks. Diesel emissions standards have "jumped the shark" and price end users are paying after warranty or in terms of down time are illogical. Wonder why VW did what they did, I don't really.

 

 

Old topic, but it sure deserves update.
Bluetec726 had bad luck with his engine. When you buy aged car, with past due maintenance and don't DIY, sure spending 10 grands to bring it back to date will not take long.
I have the same car he did and it is desirable vehicle, where I have to control my foot on cornering, or take it sideway. I am planning to sell it in next few months as I felt in love with newer 4-banger Bluetec.
That engine, while with only slightly lower performance (will burn good tires on dry asphalt) can make 60 mpg at highway speed, or average close to 40 even we don't drive for economy.
Way easier to work on as well.
Bad part about new MB is that they require SCN coding, what adds to cost when you DIY, but heck, when I save 2 grands year after year on fuel, I can pay stealer $250 for coding every couple of years.
My friend drives Honda with 260k miles. Serpentine belt was never removed in the life of the car and still looks good. I had to see it once he mention that.

 

 

 

 

What makes you thinking dealer will find the leak?
You think they will wave the troubleshooting fee if they don't find the problem?
Sad part is that Kentucky is not really MB country and even less small diesel country.
You go to California, you can drive 1 mile in industrial area to find 3 MB independent shops.
Frankly when I drive MB in central states, I am fully aware that more complicated problem might come with 1000 miles towing, or waiting couple of weeks for local dealer to learn the technology.

 

 

Good to hear you have MB mechanics in your city.
OH how about $10 bet that dealer will present you with $5000+ job estimate without finding actual leak?
For this MY the $150 autotell will do engine smoothest test and injectors quantity.
If you don't start at least DIY troubleshooting - you will leave way more at the $hops than you already have.

 

 

 

The problem with the modern Bluetec diesels is that DIY is almost impossible, There are almost no aftermarket parts and OE parts are super expensive. For many repairs, dealer is best or only choice. Indy would have to buy parts from them anyway, would need MB Star system and may not have same experience in doing repair. Then there is that SCN coding on some parts. https://www.benzworld.org/forums/gen...repairers.html

I just traded my 2014 diesel. Sad day really, because I hadn't yet had a moments trouble with it in 5 years. I love what used to be the simplicity of diesels, but they have become too darned complex. Luckily, still have the W123

 

 

My dream would be to find a W126 300SDL (86/87) that has been babied. Even a low mileage W126 gasser from early 90s wouldn't be bad.. Last really well made Benzes. But W124s not bad either. Just couldn't love those plastic side panels.

How about a Benz diesel from mid 2000s just before the DPF/Bluetecs kicked in? What years/models would they be?

 

My father gave away 1987 W124 300DT as nobody wanted to offer him even $2000 for it.
"can work on it" is loose term. I bought that car at over 20 years of age for my youngest son going to college.
But later I found good deal on W210 diesel, so by coincidence at the time - my father wrecked his Toyota and bought the W124 from me. I made the car perfectly dry, found nice seat skins, so the car was very nice and only paint job could use refreshing. But it still was old clunker and one of most popular topic in W124 section is how to delete maze of vacuum logic system.
I was thinking about W126, and the coupe from "Road house" is my favorite scene, but big, heavy car with 112HP diesel simply is not standing up to competition, while the 560S can really dent your wallet at gas pumps.
That said, in San Francisco area bunch of them are still daily drivers.

 

See in bold above. My take on this after hyperventilating over the OM642 for the last year? Delete all the anti-pollution crap and the engine shines, restore MB's legendary reliability.

 

I had had no problems in 5 years. But you guys scared me off keeping the GLK. Traded it yesterday. Cost me $15k +tax to get a fully loaded 2019 Outback - At least under warranty for next 3-5 years. Mainly for snowbirding is USA.

But sad to hand the pristine GLK over

 

I joined the ex-MB diesel club a few weeks ago also. My warranty only had a few months left and I was tired of worrying about all of the diesel problems posted here. At 48K I had the Ad Blue tank heater replaced under warranty and decided to call it quits. There's way too many similar problems to call it negative blog bias. These cars are problematic and way too expensive to repair. The cost of diesel, at least in CA, is much higher than even premium gas here so the fuel savings are not even a factor anymore.

I can't say I didn't enjoy certain aspects of the car like the torque, handling, and styling but that didn't exceed my long term ownership concerns. I'm a member of three other different car blogs and you just don't see the extensive problems that you see with the MB diesel OM642 engine. If you're not an experienced DIYer or don't mind all the costs and inconveniences of these cars maybe you can look past their drawbacks.

I've enjoyed this board and want to commend everyone for their valuable input and overall politeness which is not always the case on other blog sites.

I've decided on a Lexus RX350 because of their quality and reliability. I also needed AWD where I live. It may not quite be an MB but it fits my needs and isn't far off. And the V6 uses regular gas

 

I might be getting too old to change the car brands, but my friend is driving 14 yo Honda with 260k miles still getting 35mpg from 4-cylinders.
The only thing he did in those years was clutch and I ask him to see the factory serpentine belt, who still shows very good condition.
I have too many cars, so I plan to sell older with 642 engine, but the one with 651 is a keeper. If I ever buy another car in the future, it is going to be electric with 800 miles radius and foldable steering wheel for self-driving.