{I will readily admit, the Mercedes-Benz BlueTec Sprinter & the Mercedes-Benz SUV’s are extremely popular.   They are great driving & very handy.    I wouldn’t mind owning one.    But, I own my own Mercedes-Benz shop & I know what I’m dealing with.   For the average owner, it’s not going to be easy or cheap.   I cannot believe the volume of calls & emails I’m getting.    Most are from owners that are already in trouble, or they just realized that are heading for trouble.    If I’m getting this many calls, I can’t imagine the heat Mercedes-Benz is getting.
So before I go off into my rant, let me say this.   Everything you’re about to read here, is strictly my opinion.   Mercedes-Benz & its dealers will never approve of anything I’m about to say.   I am “persona non grata” with Mercedes-Benz.
I’ve spent the last 50 years working exclusively on Mercedes-Benz.    Twenty five for them, & twenty five on my own.   I’m certain Mercedes-Benz will tell you I don’t know anything about anything.   I’ve also heard owners tell me their local mechanic is not thrilled with going along with my suggestions.   I totally understand where they’re coming from.   They don’t want to stick their necks out & go against the factory recommendation.   If something happens, they don’t want to get blamed for some stupid idea the customer found on the internet.    There are customers who look for someone to blame when anything goes wrong with their car.    BlueTec’s are very hard to work on, & any mechanic that truly understands a BlueTec is extremely skilled.   He doesn’t need to go looking for more trouble.    If you’ve found a good mechanic to work on your BlueTec, count yourself very lucky.   It’s gotten to the point where I don’t care if we ever see one again.    Don’t expect your local mechanic to go along with anything I’ve got to say.

Mercedes-Benz has some very smart guys working in their Technical Service division.    They actually know what the problem is & could solve it if the regulators & accountants would let them.   You can forget about talking to anyone from Technical Service; they don’t talk to customers.
I’m not encouraging anyone to disable or circumvent the emission control systems on their BlueTec diesel.   Quite the contrary.   My recommendations are intended to keep your diesel operating at peak efficiency & that includes the emission system.   Please don’t call me about disabling the emission system.
Proper maintenance allows the engine & the emission system to operate as it was designed.   Proper maintenance may seem like it’s more expensive at first, but I can assure you it’s less expensive than the alternative.
This article is also generating a large number of calls & emails from owners wanting help with other technical problems.   I feel bad when people spend a lot of time explaining their problem & they aren’t finding anyone to help them.   This is actually why I wrote this article.   It’s much simpler to keep a BlueTec maintained, then deal with all the other problems.   I just don’t have time to research complicated problems.    Most of the problems people send me, are issues that require a skilled diesel mechanic to resolve.   These problems are hard enough when you have the vehicle.   When the vehicle is 3000 miles away, it’s not possible to give people a simple answer to their problems.  When you find a good diesel mechanic, hang on to him like he’s gold.}

Mercedes-Benz has pumped out so much misinformation about their BlueTec diesel, even a dealer with the best intentions, doesn’t know what to tell owners.   It’s not the dealers fault.   They have to comply with what the manufacture tells them.    They can’t go off the reservation & tell owners what they really think.    Likewise, the manufacture has to comply with what the EPA & CAFE tell them.   And so it goes.    Hats off to Ford for having the guts to tell the EPA & API that the new “super duper” diesel oil is junk.    I’m sure they will pay a price for standing up to the EPA.    Because of their legal problems, Mercedes won’t stick their necks out & give clarity to their customers.
Mercedes-Benz has their own rating system for diesel oil.     MB229.52 is the current approved diesel oil.    It is a 5W/30.   Mercedes original BlueTec oil, was rated MB229.51.    MB229.51 is no longer approved.    The problem is, you can find MB229.51 in every auto parts store in the country.
Oil companies made tons of it, & they’re not about to throw it away.   The label says it’s approved by Mercedes-Benz, but it’s not.   You’ll have a hard time finding the real “approved” MB229.52 diesel oil.   Don’t worry about it, they are both junk.   Manufactures, the EPA, & the API have all made diesel oil as confusing as possible.    Manufactures have their own oil rating, because they want a cut of the oil profit.   Europe has it’s own rating system, & it doesn’t match up very well with the U.S. system.
As of 12/1/16, the EPA/API released their own new diesel oil rating, CK-4.   It can be 5W/30 or 15W/40.    It was suppose to be the greatest thing since sliced bread.    But just to keep you guessing, Mercedes doesn’t say if their diesel oil, MB229.52, is the same as the CK-4.    It is, but once again, it still doesn’t matter.    All these oils will ruin your engine; especially if you do lots of stop & go driving in cold weather.    The EPA/API says the CK-4 oil was designed to address the problems with earlier diesel oil.   For model year 2017, the EPA/API has a totally new diesel oil rated FA-4.    They say it’s only for 2017 diesel engines.   It is not backwards compatible.   Here’s a little tip.   Whenever you hear it’s not backwards compatible, it’s junk.    Whenever you hear it’s for fuel economy, it’s junk.   All these oils are designed to meet CAFE government mandated fuel economy standards.    The EPA could care less if it turns to sludge 5 miles after the warranty expires.    Ford couldn’t put up with the nonsense anymore & announced; “Ford engineers are recommending that Ford diesel owners NOT use new CK-4 motor oils after company testing of some of those formulations revealed accelerated engine wear on some of the Ford 6.7-liter engine components in the engines they tested.   The CK-4 category was released by the American Petroleum Institute (API) for use in diesel engines last year.   Ford is advising dealers, installers and owners to use Motorcraft® diesel engine oils meeting the company’s new diesel specification, WSS-M2C171-F1.   It contains the requirements of CK-4 plus additional engine protection properties required by Ford.   In addition, Motorcraft oils with CJ-4 and CJ-4/SN specifications can still be used, according to Ford engineers. Those oils will be phased out in late 2017.”    What the heck does all this really mean?   Fuel economy oils are the bare minimum to protect the engine & meet the fuel economy standards.   “Minimum” is the operative word.    Just in case you’ve been living under a rock, you may have noticed the Justice Department has just about indited every diesel automaker.   They are all charged with fraudulently programming there diesel emission systems.   This may tell you something about modern diesel engines.   Manufactures can’t make them meet emission standards, without stupid levels of heat.   The heart of the problem is extreme heat.   The diesel oil the EPA allows, cannot take the heat.   This problem is not unique to Mercedes-Benz.    Truth be told, motorcycle oil is currently the best type of oil on the market.   The EPA & API don’t regulate motorcycle oil…. yet.    Oil companies can blend motorcycle oil with all the best additives to protect timing chains, crankshafts, camshafts, Turbochargers, & diesel emission systems.   You’ll also notice motorcycle oil is a lot more expensive than diesel oil.   (Some people say it’s more expensive because motorcycle riders are stupid & will pay more.)   If you took the time to read & understand the Material Data Sheets all oil companies are suppose to publish, you would see where the oil is better.   Here’s another tip; if the oil company doesn’t publish a Material Data Sheet for their oil, forget it.    There are many excellent motorcycle oils.   I like Redline 20W/60 in warm weather & 10W/40 in sub-zero weather.   Again, there are many excellent motorcycle oils.   Ester based synthetics are the best.   Redline is easier to find, that’s the main reason.

Most BlueTec diesel problems are actually caused by the “approved” diesel oil.   This article will try to explain how interconnected all these problems are.   The sooner owners get on top of the maintenance, the fewer problems you’ll have.   Once you’re out of warranty, it’s to late.   Depending on how you drive & where you live, it will be tough to get back to a healthy engine.

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240D & 300D owners fondly remember how rock solid dependable their old diesels were.   So they smelled & belched out black soot; that was part of the “ambiance“.   Thankfully those days are long gone!   The black soot & ridiculous NOx (Nitrous Oxides) can no longer tolerated.    BlueTec diesels are nothing like their grandfathers.   Mercedes-Benz BlueTec diesel passenger cars & Sprinter vans have great power & excellent fuel economy.   They will run fabulous, right up until they don’t.   As you drive along with the A/C on & doing your stop / start errands, owner’s are oblivious to what’s going on under the hood.   If you’re driving your Airstream Sprinter through the mountains, the turbocharger is screaming its brains out.   If you could see it at night, it would be glowing red hot… for at lease an hour after you shut it off.    The oil in the red hot turbo is the same oil that’s in the engine crankcase.   No oil can take that heat.    Mercedes & others, went cheap on the turbo.   It should have its own oil tank with a oil pump just for the turbo.   It should have Jet engine oil & the pump should run after you switch off the engine, so the poor turbo can get itself cooled down.    But that would have cost a extra $1000, & the bean counters don’t know a hot turbo from a hot potato.    The typical owner goes through a series of enormous repair bills with no apparent end in sight.    Check Engine lights, blown Turbochargers, & oil leaks.   The engine quits running & later restarts.   It doesn’t run quite right & you head for your dealer.    Sometimes the radiator hoses blow off before you get there.    The dealer will tell you they’re not sure what’s wrong, but they want to tear down the engine.    Save your money, the engine is ruined.    Owners are in shock.   I get a half dozen emails every day; “how could this happen?”   “How can I get Mercedes to pay for it?”   Then they get mad & threaten to sue Mercedes.    Save your money & blood pressure.   Most of the time the repair cost will exceed the value of the car.   If you still want to fix it & manage to find a engine, it must be a genuine Mercedes-Benz factory rebuilt engine.   My Mom always said, bought wisdom is the best wisdom….. providing you didn’t pay to much!

Here’s how a BlueTec works & 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.   From a emission control standpoint, this is also the toughest to meet.    The problem is, the EPA believes in a “one size fits all”.    In order to meet the emission standard for Boston, the BlueTec’s sold in Miami are identical.    To meet emission controls in cold weather, they need to get the engine up to operating temperature as fast as possible.   That & fuel economy, is the reason 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, 5W/30 oil & the belly panels are a major problem in hot weather.

98% of the dealer mechanics hate BlueTec’s & want nothing to do with them.   Dealer mechanics work under the “Flat Rate” commission system.   They loose money every time the Dispatcher hands them the keys to your diesel.   There is no end to the Check Engine lights, oil leaks, & comebacks.   Customers complain that their car never gets fixed the first time & it cost a fortune.   Most owners think they can treat a BlueTec the same as a gas model.   Most owners actually think they bought a economy vehicle.    Lots of diesel owners brag about using the cheapest oil they could find at Walmart.    These people actually think they are maintaining their BlueTec.   By the time a neglected BlueTec is out of warranty, it‘s a nightmare for a mechanic to fix all the problems, without cleaning up the past neglect.   Customers don’t believe they need to clean up the mess in their engine, & they won’t pay for it.    It’s a guaranteed Come Back.   Customers bounce from shop to shop, because no one wants to face the fundamental problems.    You probably thought your car is covered by a new car warranty.    After multiple visits & a mechanic has thrown thousands of dollars in parts at your problem; even Mercedes-Benz won’t pay the bill.   Mercedes kicks back the warranty claim & the dealer gets to eat the mess.    {Once the engine starts leaking oil, there is no cheap way to fix the problem.    I’ve actually come to the conclusion, owners are better off if they ignore the oil leaks.   Continue to change the oil & air filters, but just drive it until it blows up.   Oil leaks are “generally”, to expensive to fix right.}   Mercedes-Benz won’t pay for properly cleaning up all the sludge mess & neither will the customer.   Mechanics are sick of trying to work around the mess & half ass fix the problem.    Owners email me all the time, saying the dealer wants them to pay for what should be a warranty repair because of “fuel contamination”.    “Fuel contamination” is dealer code for “we’re sick of working on this mess & we’re not spending any more of our money to fix your BlueTec”.    When you hear that, start haggling with the Sales Department for a trade-in on a new “gas” model.    Better still; save yourself the grief, & lease the BlueTec for the warranty period.   Buy the Mercedes Maintenance program & let them change the oil every 20000 miles.   At 50000 miles, give them back their worn out pile of junk & get another one.   If you can’t afford to do that, you really can’t afford a BlueTec.   Never buy a used one.   Stop calling me & telling me about the good deal you’ve found on a used BlueTec with a slight ticking noise.

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!
This is where things get 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 95% of the BlueTec problems.   The right engine oil is the key to BlueTec happiness.   Here’s where you get my disclaimer.  This is all my opinion & NOT approved by Mercedes-Benz.   In fact, they will void your warranty if you tell them.   Then again, they’ll void your warranty if you use their previously recommended MB229.51 oil.    This is the oil they tell you to use in your Owners Manual.    This oil is still widely available in most auto parts stores at a cheap price.    It will ruin your engine.    (I know, it’s stupid.)

BlueTec diesel’s run exhaust temperatures of 1400°F.   If you drive in the mountains or haul a lot of weight, the exhaust temperature can reach 1800°F.   This heat is transferred straight into the engine oil.   Oil is like water, in that when it gets hot, it boils off steam / vapor.   This vapor is called “Noack Volatility”.   This & the “Viscosity Index” (VI), are the most important things know about a oil.   I’ll explain more later.   Confusion comes from all the different ratings applied to diesel oil.   This is no accident.   Everybody involved is trying to make money from their recommendation.   This is going to hurt your brain, but here goes.   For our discussion, there are two “governmental” oil rating agencies.   API (USA) & ACEA (Europe).   Then you have the auto manufactures. They want to make money on oil changes, so they all have their own oil rating that‘s different than API & ACEA.   The API newest rating number for BlueTec diesels, is CK-4.   The ACEA has C4 or E9/12.   They are all officially approved for BlueTec diesels, but Mercedes likes to say they‘re not.  Viscosity is another matter.   Mercedes says the oil needs to be 5W/30.   Most other diesel builders use 15W/40.   Low viscosity oil is for cold (sub-zero) weather & fuel economy.   High viscosity oil is for hot weather, fuel dilution, & it keeps the oil from turning into sludge.   All the “approved” oils will have the Sulphated Ash, Phosphorus, & Zinc greatly reduced.    They call it “low SAPS”.   They say it protects the Diesel Particulate Filter (DPF).   The DPF traps the black soot.    The problem is, your engine likes the Sulphated Ash, Phosphorus & Zinc.   And, this is where I part ways with Mercedes & the EPA/API.    Screw the DPF.    The “approved” oils are ruining the rest of the engine simply to protect the DPF.   It’s easier / cheaper to deal with a dirty DPF, than to replace the engine & the rest of the emission system.    I know this scares lots of people.   Owners don’t understand all of this oil stuff & it’s easier to give Mercedes the benefit of the doubt.   “They built it, they should know what oil to use!”   They do know, they just can’t tell you.    All manufactures have to comply with the EPA & API regulations.    All oil companies have to build approved diesel oil to the EPA & API standards.

This is where this gets real technical, so I‘ll try to keep it simple.   The OM642 diesel has fundamental design problems that get worse with the miles.  The sooner you get ahead of the maintenance, the fewer problems you’ll have.   Most of the problems with the BlueTec engine & emission system, are all related to each other.   Once they start, it’s a cascade effect.   Often we’ll 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, any mechanic will need a maintenance baseline.   Fluids & filters need to be current, i.e. clean.   It’s often hard to know how slugged up the engine actually is.   Add “engine oil flush” to the old oil before you drive to the shop.   This will loosen the sludge & let it drain out.   Software updates for the engine control module, must be current.   For example, Mercedes has updated the software for the BlueTec ECU, 23 times at last count.   (You might say they have a problem, & you might be right.)   The old ECU software injects to much fuel & it dilutes the engine oil.   That’s one reason we need 20W/60 oil.   60 weight oil fights “fuel dilution“.   If you start out with 5W/30, it doesn’t take much fuel to lower it to 15 weight viscosity.   After 5000 miles of normal driving, the engine oil is half diesel fuel.   We also want 60 weight oil to maintain the oil’s “Viscosity Index (VI)“.   The higher the “VI” on the Material Data Sheet, (190 is great) the better the oil stands up to heat.   The viscosity index of an oil is a measure of its tendency to change viscosity with temperature changes.   The higher the viscosity index (VI) the more consistent an oil’s viscosity is with temperature changes.   The lower the “Noack Volatility”, (5% is great) the better.    Guess what? Mercedes does not publish this data for their MB229.52 oil.    Why not?    Because it’s nowhere close to the best quality.   The EPA/API allows a maximum of 13% “Noack Volatility” for diesel oil.    I suspect Mercedes MB229.52 oil is at the maximum 13%.   That means, 13% of the oil turns into vapor when the engine is hot.   It’s that vapor that gets sucked into the Turbocharger & the DPF.
Quality oil companies are proud of their oil & publish a Material Data Sheet which spells out the technical data for their oil.   It’s the only way you can actually compare oils.   A better oil with high “VI” & a low “Noack Volatility”, will not get sucked into the DPF in the first place.   It’s only crappy oil that meets the low SAPS standard.
Also, never run Bio-diesel.   When it gets in the engine oil, & it always does, it makes a BIG mess.   Noack Volatility comes from the base stock of the oil.   There are no amount of additives that can improve the Noack Volatility.    Ester base synthetics with have the lowest Noack Volatility.   Ester synthetics are always the most expensive oils.
The Air Filters also get plugged up very easy.    Early BlueTec’s have 2 air filters.    Later models have one.    One filter is better.      In service bulletin LI07.07-P-048060, Mercedes hints at changing the air filters every 18500 miles.   They can’t just come right out & say it in plain English, so they put it in a bulletin that customers will never see.    Your Owners Manual still says 40000 miles for air filters.     Remember the part where Mercedes said to reduce oil change intervals if you drive in “severe operating conditions”.    Owners think that means the Baja 1000.    Actually, it means “stop & go city driving”.    Every set of air filters we see with 18500 miles (where they came up with that stupid number, I’ll never know) is plugged solid with bugs & dirt.   Air Filter replacement is critical.    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 the air filters several times.    The Oil Separator has been update 11 times at last count.    It’s the Oil Separator that allows the boiling oil vapor (Noack Volatility) to be sucked into the Turbo Charger in the first place.    From there, it enters the rest of the emission system.    Mercedes only put one Oil Separator on the right side of the engine.    This is a poor design & also adds to the problem of hot oil vapor not returning to the crankcase where it belongs.    Mercedes tried to cut cost by not putting a Oil Separator on both sides of the engine.

Mercedes & others, make it sound like “Low SAPS” is some super duper oil that’s better for your diesel engine.    The MB229.52 5W/30 oil Mercedes “recommends”, vaporizes much easier when it gets hot than a 20W/60 oil.    It’s just like the steam coming off boiling water.    In their service bulletins, Mercedes bends over backwards to say this hot oil vapor is “normal”….. until you’re out of warranty.    If you use a better oil with a high VI rating, a high Flash Point (over 400°F), & a low Noack Volatility rating; you will prevent 95% of the problems that plague the BlueTec.    The sooner you start, the fewer problems.   (Once again, this is not approved by Mercedes & they will void your warranty; if you tell them.    I realize going down this road takes a real understanding of how oil actually works.)
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 oil cooler & out the drain holes in the block.    The Swirl Motor Valve downstream of the Turbo also fills with hot oil vapor.    Once this oil & sludge begin to accumulate, the valve becomes inoperative & blows a fuse that controls many other sensors required to properly operate the engine & emission system.    This will immediately place the vehicle into limp home mode & limit the rpm to 3000.    It also causes a check engine light & numerous OBDII Codes.    If you’re really lucky, the metal flaps of the Swirl Valve break & get sucked into the engine.    Mercedes admits to Timing Chain failures on all 2011 to 2015 OM642 Diesels.   Zinc helps prevent the Timing Chain from failing.   2000ppm is a good number.   Most “diesel” oils have half that amount.   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.   The newest diesel oil ratings from the SAE, are CK-4 & FA-4.   CK-4 is for 2016 & older.   FA-4 is for 2017 diesels.   Most people think newer is better.   Not true when it comes to diesel oil.   If you’re to nervous to really trust a 20W/60 Motorcycle oil, you can use any CJ-4 15W/40 oil & it will be 100% legal with the Mercedes warranty.   They say the 2017 FA-4 is NOT backward compatible.   That’s code for “it’s junk”.   I wouldn’t use it in my lawn mower.

When new customers come in with their 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.     There is a company that we use, that will scan all your car’s control modules for the latest software.   If there is later versions, the modules can then be updated to the latest versions.   This is the first thing that must be done when a mechanic is chasing a hard problem.
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.   The reality is, it’s likely you’ll need to replace many of these parts at some point.

Depending on where you live, you can have completely different issues than a different part of the country.   Vehicles that drive short trips in freezing weather, will have far more problems than the same vehicle driven at higher speeds in warm climates.   Cold weather causes condensation to build up in the oil & that makes matters worse.    If you live where it’s often below freezing, I would use the 5W/30, CK-4 oil, & change it every 3000 miles.    Switch to the 20W/60 in the summer & go 5000 miles.
To summarize, what oil to use in different areas & driving conditions.
Stop & go city driving in sub-zero weather.   Use the 5w/30 CK-4 rated oil.   Change every 3000 miles.    Brand doesn’t matter.
Below freezing weather & mountain driving.   Use 15W/40 CK-4 rated oil.   Change every 3000 miles.
Everything else, use 10W/60 or 20W/60 & change every 5000 miles.    First choice is Redline 20W/60 Motorcycle oil.    Motul 300V 20W/60, Liqui Moly 20W/60, Amzoil Motorcycle oils are all excellent.   The EPA has not started messing with motorcycle oil, yet.    There are other excellent oils in the 20W/60 motorcycle range.   They may or may not have the CF rating, it doesn’t matter.   (I know, that’s not what Mercedes says.)    If you insist on sticking with the MB229.52, use BG “DOC” in every oil change.    You can get it on Amazon or Ebay.    (I honestly wish we didn’t have to concoct our own oil for diesel engines.   I totally understand the sophisticated chemical mixture that very smart people blend into oil.   This is not simple.   But something is drastically wrong with the way the rules are now written.    One thing is certain, the EPA won’t pay for your slugged up engine.   The most expensive & best oils are now made for high performance motorcycles.   Specialty oil companies now make top of the line oils that don’t have any approval rating for anything.   They are made for people that actually understand how oil works today.   These oils cost between $20 & $30 per quart.   Motorex makes a 20W/60 for KTM racing engines.    If price is no object, Motorex can take the punishment a BlueTec diesel can dish out.   If I owned a $250000 Airstream, I would use the Motorex.)
Run DPF fuel cleaner on every tank of fuel.
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.
Put 2 bottles of engine oil flush in your oil right before you drive in for a oil change.   It will help break up the sludge.   Liqui Moly Engine Flush is very good.   Every oil change.
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.
Engines with the 13 quart oil pans, are way better than the 8 quart oil pans.   In late 2013, Mercedes started bringing in those engines.
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 & 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.   Motorcycle oil can handle it, if you change it every 5000 miles.
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.
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.
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.
Get the latest software updates for you engine ECU.    As of this writing, Mercedes has 23 updates to the software, & this is very important for the life of your engine.   Mercedes doesn’t tell dealers what the updates do, but I believe they are trying to reduce the fuel injected for the DPF regeneration.    Excessive fuel washes into the crankcase oil.   That causes fuel dilution & sludge.    Fuel dilution is another reason for the 20W/60 motorcycle oil.
Drive it like you stole it. It helps keep the DPF clean.
We’ve found the owners who drive long distances at high speeds, have the fewest problems.