When I first wrote this article four or five years ago, my intent was to help my local customers better understand the problems they were having with their BlueTec diesels.     Understanding the problem, is the first step in finding a solution.    I knew preventive maintenance was the only way my customers would ever be happy with their BlueTec.      The problem is, BlueTec diesels are the most complicated vehicles Mercedes makes.     Most people would never take the time to understand the problem.     They actually have lives & other things to do.     “Mercedes built it, let them figure it out.”     Owners were bouncing from one big repair bill to the next & complaining to anyone who would listen.      I hoped this article would gradually educate my customers & also make my life easier.      Currently Mercedes-Benz only sells the OM642 V6 BlueTec diesel in America.     They recently dropped the 4 cylinder OM651 diesel.      The OM651 has similar issues as the OM642, but Mercedes didn’t sell nearly as many.      
Five years later, & I’ve retired.       But this article has kept growing.      No one is more surprised than me.      As it grew, my mechanics started to complain about phone calls from people thousands of miles away.    My guys wanted me to take the article down, because the phone calls were interrupting our normal work flow.     They had a point.     I never quite knew what to do with it.     With all the Diesel engine problems in the News, it didn’t seem like Mercedes had a handle on maintenance.      The article didn’t cost me anything, but it wasn’t a financial benefit either.    
As you know, there are plenty of people complaining about the OM642’s problems.      Lately, a few people have ask what qualifies me to hand out “free advice” on the BlueTec’s problems.     I grew up in a small Indiana farm town in the 1950’s.     Self promotion was not an admirable quality.     In those days, you just did what you said you would do.   If I didn’t, everyone knew my Mom, & she definatly knew where to find me.     For what it’s worth; in 1967, I started working for the Mercedes-Benz dealer in Indianapolis as a way to work my way through college.    (In those days, you could actually work your way through college & not be in debt when you finished.    Those really were the good old days!)      I was a Mechanic, Shop Foreman, Training Instructor, & finally, the Service Director for two Mercedes-Benz dealerships.    Mercedes-Benz gave me the “Star Technician” award once & the “Mercedes-Benz Service Manager of the Year” award 5 times.    Twenty-five years ago I started my own Mercedes-Benz shop.    I retired at the end of 2017.     I defiantly don’t know it all, but I do know how a BlueTec diesel works & how to keep it working.

Mercedes-Benz installed the BlueTec Diesel engine in passenger cars & Sprinter Vans.    They also put the OM642 V6 diesel in Dodge Vans, Freightliner Vans, & Jeeps.    Regardless of which body it went in, all BlueTec’s work the same way.    In 2007 & 2008, when Mercedes first came out with the OM642 diesel, they called it a “BlueTec”.     It wasn’t.     “BlueTec” means the emission system has a DEF (Diesel Exhaust Fluid) tank.     Also known as “AdBlue”.     (Mercedes loves its acronyms.    For normal people who are not into all this tech stuff, I’ll try to explain them as I go along.)         2009, was the first year the Mercedes-Benz OM642 diesel actually had DEF fluid or AdBlue, injected into the exhaust.      They inject the DEF into the exhaust to reduce emissions.      Except for the DEF fluid, all OM642 V6 diesels operate the same way.     All OM642 diesel’s have a DPF, (Diesel Particulate Filter, which traps the black soot in diesel exhaust).      The engine does not need the DEF system to operate.     Then why does the engine run to badly when something goes wrong with the DEF system?     When the DEF system has a problem, the DEF computer tells the engine’s computer to stop running properly.    Mercedes calls this “Limp Home”.      When the engine switches to “Limp Home”, it lacks power.     Warning lights come on, & if you ignore the warning lights, the engine computer won’t allow the engine to start.      If the DEF system computer (SCR / Selective Catalytic Reduction) couldn’t talk to the engine computer (ECU / Engine Control Unit), the engine would never know it was there.      Mercedes has admitted, that 100% of the 2009 to 2015 DEF fluid tanks will fail.     That’s right, 100%.
All Mercedes diesels have exhaust driven, air / oil cooled Turbochargers.     Why is that important?     The Turbocharger forces more air into the engine than if it wasn’t there.     That gives the engine more power.     Something has to cause the Turbocharger to spin real fast & force that extra air into the engine.     Engineers use the engine’s own exhaust gas to spin the Turbocharger.     The problem is, the exhaust gas is real hot.     Remember the DPF?     Every so often, the engine has to burn the soot trapped in the DPF.     To do that, the engine’s computer has to inject a lot more fuel to “regenerate” the DPF.    Now we’re really cooking.     In fact, when you’re driving up a steep mountain & you’ve got your foot on the floor, the exhaust gas can go even over 1600F.      That means your Turbocharge is running at over 1600F.      This is technically known as “Red Hot”.      There are some people who don’t believe this.      I invite you to the Garrett Turbocharger website.    Garrett makes the Turbocharger’s for Mercedes-Benz.      Read the FAQ section.     You would think Mercedes would have a way of cooling your Turbocharger?    Not really, & this is a major part of the problem with the OM642.     Your Turbocharge is lubricated with the same oil that’s inside your engine.     When your engine oil hits your Turbocharger, it is super heated to a temperature far beyond what it was ever designed for.     That’s why Mercedes is having so much trouble with the engine oil.   It doesn’t take long before all the oil in the engine is boiling hot.    This is why the NOACK volatility number for the engine oil is so important.
(More about NOACK later.)      Other than oil & air, there is nothing else cooling your Turbocharger.     Why would Mercedes build a engine with such a obvious problem?     You know the answer, “money”.      Garrett makes water cooled Turbochargers that run cool.    They also make Turbochargers that have their own separate oil tanks with special Jet engine oil that’s designed for extreme temperatures.     Mercedes even offers these Turbochargers on military & emergency vehicles.     But those aren’t available to the public.     The cost of a proper Turbocharger would add $2000 to the vehicle.    If the OM642 had a proper Turbocharger, it would last for 30 years.    Do I need to explain more?

So the OM642 is what it is.     How do we solve the problem Mercedes has given us?      Over the last 10 years, the Mercedes maintenance schedule for the BlueTec diesel has been….. less than helpful.       The last ten years have cost owners dearly.      It’s not only the needless repair bills, but now governments have also retaliated.      For 2018, Mercedes finally published a decent maintenance schedule in their Sprinter BlueTec diesel owners manual.     Even with all the OM642’s design problems; if Mercedes had started out ten years ago with the 2018 maintenance schedule, they would have saved owners & themselves a lot of money & heartache.      For 2018, Mercedes-Benz has significantly changed their diesel maintenance recommendations.     They’ve finally come around to the same maintenance schedule I’ve advocated for years.      The change had nothing to do with anything I said.    They finally got tired of all their mad customers bad mouthing them around the world.     Think of it, it has taken years, to finally get a clue.      You can check out the new diesel Owner Manual on their 2018 Sprinter website.     Sadly, their old ways are not behind them.      Mercedes makes no effort to inform the owners of prior model years of these changes.      I’ve already given the maintenance section from 2018 Owners Manual to some readers.     When they show it to their local Mercedes dealer & try to get them to switch,  the dealers won’t go along.     Owners like you, are being told; “the 2018 schedule doesn’t apply to the older OM642.     “Only the oil that came in your vehicle is approved”.     The factory even says they reserve the right to change the maintenance without notice, but changing their dealers is a different problem.     Think about it, if a dealer can’t understand what’s written in the owners manual, how can they possibly understand Mercedes technical manuals?     Not all dealers are this way.    In fact, most try hard.      But for those of you who are having trouble with your dealer, now you know why.
The new 2018 diesel oil change intervals are twice a year.     Change the oil at the start of summer & winter.     No more 10000 & 20000 mile oil change intervals.    The average owner drives 10 to 12 thousand miles per year.     I’ve heard some owners think it’s so the dealer can make more money.     No, these engines desperately need frequent oil changes.     Mercedes also is now approving higher viscosity oil.    10W/60, 15W/60, & 20W/60 weight oils are now approved.     Mercedes even explains why.    Intermittently, the engine’s computer has to inject extra fuel to regenerate, or burn off, the soot in the DPF.    Some of that extra fuel washes past the piston rings & into the crankcase oil.    This is called “fuel dilution”.      Heavier weight oil is needed to deal with fuel dilution.     Mercedes finally explains this in their 2018 BlueTec owner’s manual.     I’ve listened to a lot of so called experts on owner’s forums & dealer personal pontificate about the evil’s of 50 & 60 weight oil.    Maybe now, they will give it a rest.
Because of Mercedes new 2018 maintenance schedule, I’ve dropped my tedious explanation of diesel oil specifications.     It was just to confusing & it appears the EPA, Mercedes-Benz, & the oil companies now agree.     I don’t think any of them have officially given up on “low SAP’s” diesel oil, I think they have decided to look the other way.    Whatever it is, something changed.       Oil companies are now formulating new diesel oils with chemical properties that are similar to their motorcycle oils.     Motorcycle oils generally have better additive packages & can withstand extreme heat better than other types of oil.     I’ve also heard from a number of Petroleum engineers who have been gracious enough to share technical articles.     One engineer sent me information about a new diesel oil with an extraordinary Material Data sheet.     Another sent me a new redesigned billet OM642 oil filter housing.     It is easy to install & now owners can use a much bigger oil filter.      It cost $599, & will greatly improve oil filtration.
Anyone that wants written proof of anything I’ve said, send me a email & I will forward you the documents.      
  
This article has taken on a life of its own.    Now that I’ve retired, I’m getting even more calls & emails, & they’re from all over the world.     In this article I’ve tried to give people solutions to their BlueTec problems.    But a lot of people want more.    This is complicated for a lot of owners & they want a personal explanation.     Even though Mercedes put the OM642 in a lot of vehicles, Sprinter owners contact me the most.     Sprinters hold their resale value much better than anything else Mercedes-Benz sells.     Sprinter owners tend to be more proactive.     They either use their Sprinter for work or for travel.      They can’t afford breakdowns.      Sprinter owners also tend to be more concerned about the environment.     If the OM642 is well maintained, the emission system works better.      I know for a fact, this engine reacts well to good preventive maintenance.      It will pay for its self 10 times over.    People are now starting to say these new diesels are throw away engines.    They think there is no way to keep them together.     I strongly disagree.     The problem is, nobody will tell owners the proper way to maintain a OM642 diesel.     Mercedes did a much better job explaining the maintenance in their 2018 Owners manual, but they are still a long ways from the plain English the average owner needs.      Then you have dealers that still won’t change.    I’ve had numerous owners tell me their dealer is still telling them they can go 20000 miles on oil changes.     Mercedes is making this much harder than it needs to be.    I know they know better, but for some reason they just want to make this difficult.

I spent so many years helping people with these diesel problems, that it’s hard to retire & just switch it all off.     However, I would rather spend my free time with my two year old Grandson.     Then one of my old Sprinter customers came up with a good idea.     I can still use all this experience & help both diesel owners & my Grandson.     I want my Grandson to have a college education.     To do that, I’ll keep helping diesel owners with their problems.    For a long time, I freely answered people’s questions & sent them as much technical information as they wanted.     But for a lot of people, the technical information was over their heads.     They would call me back with questions that were answered in the information I sent them.     This stuff is complicated & people wanted a someone to walk them through this & give them a written plan, A to Z.    I’m sympathetic, but I already did my 50 years.     If not for my Grandson, I would let the website expire.     But right now, I’m highly motivated to see that he goes to college.    So, for $200, I’ll help BlueTec diesel owners with their problems.     I’m currently getting about 15 calls & emails per day.     I originally thought we could do this on the honor system, but that didn’t work.    Some people were sending me dozens of emails & phone calls.     They would send me their repair orders & estimates for thousands of dollars in repairs.    After spending many hours helping them sort through all of their problems; you guessed it, they forgot to send the money.     Then there are the guys who’ve taken their engine apart & can’t get it back together.      They want me to talk them through it.      They also forgot to send the money.     It went on & on late into the night.     About half the people appreciate the help.    Now I’ve set up a PayPal account to fund my Grandson’s college savings account.     If after reading this article, you want more help, email me at ‘tom54stephens@gmail.com’.     Let me know what your problem is.     If you just want a maintenance plan, tell me where you live & how you drive.    Tell me your model & year.     How many miles & a brief service history.      If you are buying a new or used Sprinter, I’ll help you with that.    For $200, I’ll answer all your maintenance questions.    I’ll explain it on the phone or email you all the instructions.     It’s not a one time thing.   If after a few weeks, you think of new questions, I’ll keep answering them.
I’ve tried to answer most of the typical questions in this article.      But there are so many things that can happen & lots of people are baffled by all the misinformation they get.       I’ll tell you where you can buy all the things you will need.      (By the way, I don’t make anything off of what I recommend.    I also don’t put any of those annoying Google Ads on the website.)      I’ll explain what oil to use for your specific situation.     There is no one oil that works for 100% of the vehicles.      If you’re having the early warning signs, I can tell you how to prevent a $30000 disaster.     There are other common failures that I can save you thousands even after it’s failed.     I’ll send you as much technical information as you want.      Proper maintenance is not cheap, but it’s way cheaper than a new engine.
People have been scared into protecting the DPF at all cost.     The DPF is no big deal.     It can be cleaned or replaced.     The engine is a big deal.       The priorities are backwards.     I’ll explain it so it makes sense & you don’t have to believe someone at the dealer who knows less than you.     If you want to figure this out on your own, or let your dealer answer your questions; go right ahead.    You’ll not hurt my feelings.     If you think $200 is to much, Mercedes charges $60 for 24 hour access to their technical website.     It’s web address is; startekinfo.com.      Knock yourself out.       If you think your BlueTec is confusing, wait until you waste a day on their website.       If you’re looking at a New Sprinter, I can tell you what options you’ll want & which ones you don’t.    For example, you don’t want Xenon headlights.   When they burn out, they can cost thousands to repair.     You can make the standard headlights just as bright as the factory xenon for a fraction of the cost.     People call me with estimates & they don’t know if it’s fair.
I will explain your problem in plain English & tell you if there is another way to solve the problem & save money.     If you want simple answers, I can keep it simple.    If you actually want to read the technical articles about your BlueTec problem, I can give you all the technical details.        If you live in a area where your local mechanic doesn’t see a lot of BlueTec’s, I can give you the technical information & the correct fault codes that will speed up his diagnostic time on your problem.      If you’re traveling & have a problem; I can send you the technical answers so you’ll have some idea about what your up against.      I’ll tell you exactly what products to use & where to get them.     I can tell you one thing for sure; what works in Seattle, doesn’t work very well in Houston.       BlueTec diesels are all serviced differently, depending on where you live & how you drive.
Sometimes the best solution is to do nothing.      Mercedes is constantly sending out updates for the computers.    They are important.    Dealers don’t want to do the updates because Mercedes doesn’t pay them enough.    I can explain how you can work around them.     Getting the dealer to do the updates is the best, but if they won’t……

I only want people to pay for this if they think it was worth it.    I won’t send you a bill or call you for the money.      People like PayPal option & it seems to work the best.     If you think what I send you is not worth it, just tell PayPal to reverse the charge.     I’ll try to do better next time.     However it finally turns out, I won’t bug you for money. 

.    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .    .

WHY IS EVERYONE SO UPSET WITH THE BLUETEC DIESEL?    Mercedes diesels have great power & excellent fuel economy.    They drive better than another Van on the market.    I love Sprinters.   The SUV BlueTec diesels….. not so much.    The SUV’s depreciate so fast, people are upside down & it’s hard to justify spending more money to save them.
On the other hand, Sprinters are unique in the marketplace.    They have long useful lives & are worth the investment.     I totally understand why people like Sprinters.     But why are there so many complaints?    Most people buy a BlueTec & they believed the salesman when he said they can go 500000 miles with no problems.     I’ll bet the salesman didn’t tell you Sprinters take special maintenance & special mechanics to work on them.     The average owner is not prepared for the maintenance cost & the aggravation.      If you’re reading this, your part of a tiny group of owners who will actually do the maintenance if someone actually explained it.
A BlueTec diesel is way more complicated than any other Mercedes made.     Routine maintenance is more expensive.     Any mechanic that truly understands a BlueTec is extremely skilled.     He is typically the smartest guy in the shop.     If you find a good BlueTec mechanic, he’s good as gold.     But even the very best BlueTec diesel mechanic will have comebacks.      Most dealer mechanics won’t work on a BlueTec because they can make more money working on easier models.      Who needs to listen to mad customers blaming them for inherent design problems that aren’t the mechanics fault.
At first, proper maintenance will seem like it’s more expensive.      I can assure you, it’s way less expensive than a new engine.    When you hear some guy telling you nothing has ever gone wrong with his diesel for 300000 miles, it isn’t true!    In the past, Mercedes didn’t want to tell owners about the proper maintenance.     They thought it would cost them sales.    Finally Mercedes is coming around.

The proper engine oil is a major factor in the life of a BlueTec diesel.     Mercedes published a great service bulletin in 2008.    That bulletin tried to explain away the most fundamental problem a BlueTec diesel stills has to this day.     The bulletin talks about oil from the crankcase being sucked into the Turbocharger.    Mercedes said it wasn’t a problem.     Well, it was & still is a problem.     Mercedes has never fixed the cause of oil entering the Turbo.     They’ve put band-aids on the problem, but that oil is where a big chunk of the problems start.     Solve that, & lots of other problems go away.    Here’s the simple explanation.     The Turbocharger is exhaust driven.    During DPF regeneration, hot exhaust gas also heats the Turbo to 1600F.     (Regeneration of the DPF is what burns off the soot trapped in the Diesel Particulate Filter.    In order to burn off that soot, extra fuel is injected & it makes the exhaust very hot.    Also, not all of the fuel is burnt.   Some gets past the piston rings & into the crankcase oil.    This is called “fuel dilution” & it makes a big mess inside the engine.)
Some people see that 1600F number & don’t they don’t believe it.    BELIEVE IT!    I can show you Mercedes own technical explanation & they admit it gets that hot.    The Turbo is lubricated with the engine’s oil.    That means the engine oil gets way to hot & it turns to steam.     The hot oil steam / vapor gets sucked out of the Crankcase vent system & into the Turbo.    That’s why the bulletin tries to say the oil in the Turbo is normal.    No, it’s not normal, & this is one of Mercedes major design mistakes.    The engine only has one Oil Separator.    It needs two.    (This is why you need a oil that doesn’t turn into a vapor so easy.)      As the oil vapor goes into the Turbo it exits into the exhaust.    The EGR (Exhaust Gas Recirculation) grabs part of the oil vapor in the exhaust & sends it back into the air intake system to be burnt again.    That oil vapor keeps building up on everything in the intake system & it finally turns into a hard carbon deposit.    This “crud” finally blocks the air flow & turns on the check engine light.     In the mean time, the oil in the crankcase keeps getting thicker as the oil vapor is boiled off.    Mix into the crankcase oil a bunch of extra diesel fuel that has washed past the piston rings & you’ve got yourself a real bucket of tar in no time.     While this is happening, the poor timing chain is trying to do its thing while slopping through this mess.     The chain stretches, & that’s the rattle noise you hear after start-up.     As that tar / sludge builds up in the engine, it restricts the oil passages to the crankshaft.    The crankshaft finally starves for oil & the engine locks up.    Simple as that!
In the past, I tried to explain all the crazy regulations around diesel oil.    They got so bizarre that I think even the regulators finally gave up.    Engine’s are frying all over the world.     Suddenly in 2018 no one is talking about “low SAP’s”.    Oil companies & Mercedes in particular, have published realistic oil recommendations.    No more 10000 & 20000 mile oil changes.    The only problem now, is they haven’t made any effort to tell past owners of these changes.   It will take several years & a lot of ruined engines before dealer personal all get on board with the new regulations.    I’ll not waste any time explaining the old regulations.
The key to understanding oil, is the Oil’s Material Data sheet.     It tells you what the oil is really designed to do.     People often say their old car did just fine with Mobil One, & that should be fine in their diesel.     Gas engine’s don’t run extreme oil temperatures.     Low “NOACK volatility” is the most important oil spec.     It tells you how much of the oil will turn to steam when it gets hot.     It’s the hot oil vapor that is killing your engine.      Here’s another tip; if the oil company doesn’t publish a Material Data Sheet for their oil, forget it.    If they have a Material Data Sheet, but it doesn’t say what the NOACK percentage is, it’s 13.5%; which is the maximum allowed by law.     (The NOACK volatility is an important pollution number & the EPA / SAE regulate the maximum allowed by law.    Any oil that’s at the maximum, is not a very good oil.)    The official Mercedes-Benz 229.52 oil does not have a Material Data Sheet.      If you want to waste some time, call Mobil One & ask them what’s the NOACK volatility for their 5w/30 ESP oil?    They refuse to give consumers that information.    They must be real proud of that oil.
Motorcycle oils typically have the best NOACK volatility scores.     But, there are some new diesel oils that have copied the chemical make-up of the best motorcycle oils & have improved on their NOACK volatility score

WHAT GOES WRONG?    BlueTec “clean diesel technology” is anything but simple.   Stop & go city driving in cold weather, is the worst possible life for a BlueTec.   Also, never let a BlueTec idle for long periods.    It is very hard on the engine.    When you first start it, give it a few seconds to wake up, & start driving.     From a emission control standpoint, this is also the toughest to meet.
This is the area that’s causing all the legal trouble.    The EPA believes in a “one size fits all”.
Mercedes sells the same BlueTec engine in Canada & in Phoenix.      There is no way this engine can run with the same oil in both climates.     To meet emission controls in cold weather, they need to get the engine up to operating temperature as fast as possible.   A quick warm-up & fuel economy, are the reasons for very low viscosity engine oil (5W/30).   It’s also the reason for the belly panels under the engine.    Mercedes says the belly panels are for “noise encapsulation” & to protect the fan belt from road dirt.    The belly panels are really there to trap the heat during warm-up.    The problem is, the belly panels add to the extreme heat after the engine is hot.
Most Sprinters don’t have belly panels like the passenger cars.
They have a felt like blanket that is form fitted to the engine.    Don’t even think about trying to remove it.

Most owners think they can treat a BlueTec the same as a gas model.    I’ve heard a lot of diesel owners brag about using the cheapest oil they could find at Walmart.     Go ahead.     By the time you run that oil for 80000 miles, you’re out of warranty & you can take all that money you saved to buy a new engine.      Before any mechanic can fix your current problems, he really needs to clean up all the past neglect.     He has to have a good baseline to begin.    A lot of customers just can’t believe they need to clean up the mess in their engine, & they won’t pay for it.    An inexperienced mechanic will try to work around all the other filthy problems.     He will wish he hadn’t, but everyone has to learn the hard way.     This is why it is so hard to find a good BlueTec mechanic.     Customers bounce from shop to shop, because no one wants to face the fundamental problems.    You have a filthy mess that must be cleaned up before your problem can be solved.     You may even think your car is covered by an extended warranty.     After multiple visits to your dealer & the mechanic has thrown thousands of dollars at your problem; even Mercedes-Benz won’t pay the bill.   (This is where I really think Mercedes owes it to their customers to explain these problems or pay to fix them.    Instead, they would rather spend their money litigating with the DOJ or their customer.)     Mercedes kicks back your warranty claim & the dealer gets to eat the repair bills.    Or better yet, the dealer blames it on bad fuel & makes you pay for everything.     Oil leaks are a particular problem caused by the extreme heat, dirty air filters, & boiling oil.     {Once the engine starts leaking oil, there is no cheap way to fix the problem.    I’ve come to the conclusion that owners are better off if they ignore the oil leaks.   Continue to change the oil & air filters, but just drive it.   Oil leaks are “generally”, to expensive to fix & do them properly.    There are a few tricks to prevent oil leaks that I can explain later.}    Under warranty, Mercedes-Benz won’t pay for cleaning the diesel oil mess & neither will the customer.   Mechanics are sick of trying to work around all the crud, so they do a half ass fix just to get rid of you.    There are seven or eight known oil leaks that I can show you how to prevent or at least slow them down.
Owners email me all the time, saying the dealer wants them to pay for what should be a warranty repair.   They blame it on “fuel contamination”.    “Fuel contamination” is dealer code for “we’re sick of working on your BlueTec & we’re not spending any more of our money to fix it.     When you hear that, start haggling with the Sales Department for a trade-in on a new “gas” model.     Never buy a used BlueTec diesel!    Stop calling me & telling me about the good deal you’ve found on a used BlueTec with a slight ticking noise.     There ain’t no good deals on used BlueTec’s!

All diesel engine manufactures must comply with the same regulations.   This is not unique to Mercedes-Benz.   To comply with the regulations, engineers had to increase the diesel combustion temperature…. a lot!    But, American Diesel engine builders went with a different style crankcase ventilation system than Mercedes uses.    The Mercedes BlueTec crankcase vent system is inadequate for the engine.    It’s the main reason American Diesel engines don’t have the problems Mercedes has.
This is where things start getting complicated, so I have to assume you have some technical knowledge or this would take forever  to explain.    If owners did a few basic things when their BlueTec was new, they would eliminate many of the BlueTecs problems.   The right engine oil is the key to BlueTec happiness.

Most of the problems with the BlueTec engine & its emission system are all related to each other.
Once the problems start, it’s a cascade effect.    Often we would see a car for the first time with the Check Engine light on.    The customer just wants to fix what’s wrong, & nothing else.    They don’t want to hear any story about maintenance.    To properly diagnose a BlueTec diesel, the engine will need a through cleaning.    Fluids & filters need to be current, i.e. clean.
Diesel engines have always been dirty, but a BlueTec is a new level of dirty.      It’s often hard to know how slugged up the engine actually is inside, but I can assure you, it’s slugged up.     You will never see it in the oil filter or through the oil cap.      The first thing, add “engine oil flush” to the old oil before you drive to the shop for its oil change.     You can get “engine oil flush” at any parts store.     This will loosen the sludge & let it drain out.
If it’s real dirty, you’ll need to refill the engine with 100% Marvel Mystery oil.     It is very high detergent & will really get after the sludge in the crankcase.     Only drive a few hundred miles with the Marvel Mystery oil.
It also helps to simply clean-up all the caked on oil grime.     Take the top plastic cover off the engine & pour Simple Green all over the engine.   Down in the “V”, there is always a lot of crud.     Spray Simple Green all over the bottom of the engine.    It’s easiest at a quarter car wash, but you can’t blast the engine with the high pressure.    Set it to a softer setting & wash off all the dirty grime.    It will drain out the drain holes in the “V”.    You can high pressure the bottom of the engine.
Software updates for the engine control module, must be current.    If you have strange problems, you will go nuts trying to figure them out.     Always update the software first.     Mercedes has updated the software for some of the BlueTec ECU’s, 23 times at last count.     Most dealers don’t want to check of your software for updates.     They loose money doing it.     The old ECU software injects to much fuel & it dilutes the engine oil.
Never run Bio-diesel.    Not even B5.    When it gets into the crankcase oil, it really turns to sludge fast.
The Air Filters also get plugged up very easy.    Early BlueTec’s have 2 air filters.    Later models have one.    One filter is better.    Sprinters have one air filter.    Dirty air filters send the crankcase pressure into orbit.   The more pressure in the crankcase, the more oil leaks you’ll have.   Mercedes has upgraded their air filters several times.
The Oil Separator has been updated 11 times at last count.     It’s the Oil Separator that allows the boiling oil vapor (NOACK Volatility) to be sucked out of the engine & into the Turbo Charger in the first place.    This is what they call the PCV valve on American engines.
The plastic Air Intake at the Turbocharger also melts from the extreme heat.    The hot oil vapor that was “normally” going into the Turbocharger; instead leaks onto the Swirl Motor & shorts it out.    That causes the engine to go into the Limp Home mode.     Oil then drips out the drain holes in the block & all over your driveway.     If you’re really lucky, the metal flaps in the Swirl Valve break & get sucked into the engine.
Mercedes admits to Timing Chain failures on all 2010 to 2015 OM642 Diesels.   Zinc in the oil helps prevent the Timing Chain from failing.   (1600 to 2000 ppm is a good number.)     Most “diesel” oils have 500 ppm.
Once again, it’s a cascade of problems that starts with poor quality oil & dirty air filters.   There are many other important qualities motor oil needs to have, but these are the basic things.

When a new customer comes in with the Check Engine light on, it’s not just a matter of fixing what the fault code says.   All the basic maintenance of the engine must, I repeat, must be clean & in good working order.    This is the number one reason these cars don’t get fixed on the first attempt.    The mechanic is trying to make the customer happy & keep the cost down.   So he tries to fix the symptom & not the cause.    The customer doesn’t want to spend the money on proper maintenance & tells the mechanic everything is in great shape, when it’s not.     Find a good mechanic & stick with him.    Even when he makes a honest mistake.     It’s very important that all the software is current in all the control modules.    Some dealers don’t like doing this & will tell you it isn’t necessary.     Before you start chasing problems, the software must be current.    When you have hard problems to solve, your mechanic needs a good maintenance baseline.     Ignore this, & you will waste time & money like you won’t believe.    Speaking of Fault Codes; they are often wrong.    The fault code may say sensor “X” is bad.    In reality, it’s sensor “U” that is bad.     I’ve kept hundreds of these fault codes & what the problem really is.
Almost all of the important parts on this engine have been updated by Mercedes to solve some sort of emission or oil leak problem.    Almost any problem the BlueTec has, is a result of the same core design problems that bedevils every BlueTec made.   It’s likely you’ll need to replace many of these parts at some point.    Starting with model year 2014, Mercedes started using a 13.5 quart oil pan.   Those engines are much better than the older 8.5 quart oil pan.

Depending on where you live, you can have completely different issues.     If you live where it’s often below freezing & make short trips, there are 5w/30 oils with very good NOACK volatility.
Much lower than the official Mercedes-Benz oil.      In subzero weather, change the oil every 3000 miles.     Cold weather is harder on the oil.    Switch to a 20W/60 motorcycle oil in the 95F+ summer & go 5000 miles.    Mild weather like San Francisco, use 20W/40 motorcycle oil with a NOACK of 2.7%.         There is now a new 20W/50 “diesel” oil with a 3.7% NOACK.     These are impressive oils that far exceed Mercedes official factory oil.
Run DPF fuel cleaner in every tank of fuel.   BG 245 is a excellent fuel system cleaner.
Keep the AdBlue tank close to full.  In subzero weather, you don’t want to risk it splitting the tank.  Use a name brand AdBlue.   Mercedes has also admitted to a 100% failure rate on all the 2009 to 2015 AdBlue tanks.   There are a couple of options when it fails.
Put 2 bottles of engine oil flush in your dirty oil right before you drive in for a oil change.   It will help break up the sludge.   Liqui Moly Engine Flush is very good, but you can use other brands with no problem.     Do it every oil change.   A quart of Marvel Mystery oil in with the new oil every oil change, will help reduce the sludge.    (I know Mercedes says not to use oil additives.    I also know about poisoning the DPF.    The engine is the most important.    Everything else is secondary.)
Get a super magnet drain plug from Dimple Magnetic Drain Plugs.   It will trap all the metal smaller than 35 microns the oil filter can’t stop.
There is a new aftermarket oil filter that is much bigger then the original.   It’s not cheap, but it will control the soot in the oil.
Take the Belly panels off under the engine.    It needs all the air flow it can get.    There really is no other way to get rid of the crazy heat.   The cooler it runs, the less stress it puts on oil seals, plastic, rubber, & electrical parts.    If you live where it’s below zero, you may leave them on.    The panels catch oil leaks that owners don’t realize the engine is actually leaking.    On the downside, your friends are going to tell you to not park in their driveway.
If you ever compared the oil filter from a 1980 diesel & a modern diesel, you would notice the older oil filters were twice as big.   Bigger is better.   Diesel oil picks up a lot of soot.   That’s why it turns black so fast.   Soot in oil is bad.   If you’re really anal, change the oil filter every 2500 miles.   The only real difference in diesel oils used to be the additives to neutralize the sulfuric acid that would build up.   But today diesel fuel is low sulfur, so there is not so much sulfuric acid.
Only the BlueTec diesel engine has Motor Mount support arms that are filled with a special grey “heat sink” material.    They are designed to withstand extremely high heat.   Engineers are trying to prevent the extreme engine heat from boiling the oil out of the motor mounts.    The motor mounts are hydraulic / fluid filled.    The BlueTec engine runs so hot, it melts the grey “heat sink” material that was designed to withstand extreme heat.    Grey sludge leaks out under the engine & causes a mess you won’t believe.   If the engine runs so hot it can melt this stuff, guess what it’s doing to the oil?    (“Engineered like no other car in the world.”)
Change the Air Filters every 20000 miles.
Fuel filter every 30000 miles.    Replace the rubber hoses to the filter.   Rubber flakes off old hoses & ruins the fuel pump.
Never use Bio-diesel fuel.   I don’t care what anyone says, it’s not worth the risk.    I’ve heard that Bio-diesel is unintentionally getting mixed up at stations by careless fuel delivery drivers.    Some stations don’t label the pump.   B5 is the only Bio Diesel Mercedes says you can use.   Don’t touch the stuff.   Refuel at busy stations.   When traveling, plan ahead & refuel at half a tank with zero Bio Diesel.   That way if you can’t find the right fuel, you can keep going until you do.
Mercedes has now started to recommend the EGR valve be cleaned every 40000 miles.   Burnt oil clogs it.   We found a way to really clean the EGR & the rest of the emission system.   We took the Liqui Moly kit for cleaning the DPF, & modified it.   We remove the sensor in the EGR pipe.   We made an adapter that threads into the EGR pipe & connect it to the Liqui Moly gun in their DPF cleaning tool.   We put BG 245 diesel fuel system cleaner into the gun & spray the BG 245 cleaner straight into the EGR pipe as the engine is running.   The BG 245 really cuts through the crud in the EGR system & it cleans the DPF at the same time.   The whole system is getting a serious cleaning.   This is simple, once you make up all the adapters to make it work.    (The adapters don’t have part numbers.    Old mechanics have drawers full of oddball fitting & they can find the ones that connect to the EGR & the Liquid Moly flushing tool.)
When you go in for service, ask the shop to do a manual regeneration of the DPF.    The Mercedes-Benz tester can force the system to clean itself.
Drive it like you stole it.   It helps keep the DPF clean.   (This is also in the 2018 BlueTec owners manual.)
Owners who drive long distances at high speeds, will have the fewest problems.
And if this wasn’t enough, I’m getting reports of Sprinter frames cracking at the rear suspension.
Dealers are telling owners the vehicle can’t be fixed & Mercedes won’t pay for it.    Some dealers have dozens of cracked Sprinters.    I don’t know what years or if they were used for towing.    It’s worth asking your local mechanic to check for stress cracks in the rear.