Most people are finding this website after they’ve had a problem with their Mercedes-Benz BlueTec diesel.   Other people find it as they research a new Sprinter.  Still others have found the link on an owner’s forum.   The article was originally written as a way to explain the BlueTec diesel to my local customers.  As time passed I began to hear from BlueTec owners all over the world. I’ve learned a lot from their thousands of stories.  If I tried to cover them all, this article would be impossible to read.  However, those stories constantly motivate me to search for a better and more concise way of conveying what I’ve learned about the Mercedes-Benz BlueTec diesel.  I worked for Mercedes-Benz as a Mechanic, Shop Foreman, Instructor, and a Service Manager for 50 years.  I retired last year.  In my opinion a BlueTec diesel is the most complicated engine Mercedes-Benz ever built.

When Mercedes-Benz introduced the OM642 V6 diesel in 2008 everyone was blown away by how fast the engine was.  Mercedes had a diesel that could out run a similar gas engine.  Mercedes mechanics thought they were witnessing the end of gas engines.  After the OM642 Mercedes came out with its smaller brother the OM651 four cylinder diesel.  After the first year the euphoria wore off.  Mechanics were slowly beginning to realize how difficult this diesel actually was.

I’m only going to deal with the hard problems in this article.  If you want to know about the vehicle features or production information, you can look that up on automotive website. Mercedes has dropped the Diesel engine from their passenger cars.  In North America the OM642 only comes in the Sprinter.  I still hear from a few passenger car owners, but most have given up. The cost of repairs is too much for most people.  On the other hand, Sprinters are one of Mercedes most popular models.  For the most part, owners love their Sprinters.  They just don’t love the maintenance that comes with the OM642 diesel.  It really is a love hate relationship.  Sprinters hold their resale value.  They drive better than any other big van.

Sprinters are used for work or pleasure.  For those two simple reasons owners have a great deal more money invested.  When you have $100,000 to $200,000 invested you don’t typically ignore the maintenance.  I’ve found that most Sprinter owners will do the preventive maintenance if they only knew what it was.  I talk to new owners all the time and they were basically told to service it once a year or maybe every 20,000 miles.

Mercedes-Benz has been building the OM642 BlueTec diesel for over ten years.  By now there should now be plenty of technical knowledge about them, so where is it?   You can find a little on some owner’s forums and YouTube has some repair advice.  They mainly discuss the most common repairs.  They don’t get into why the repairs were needed in the first place.  I’ll be the first to admit I can never seem to find the best place to start.  Explaining a BlueTec is like peeling an onion.  Every time I think I’ve got it covered, there is another level… and then another… and another.  I suppose that’s why you don’t find anyone else trying to explain this thing.

Diesel engines are inherently dirty.  Practically every problem with a BlueTec engine has its roots in the emissions system.  Soot is the most obvious emissions problem from a diesel but not the only problem.  Soot is the black smoke you see in diesel exhaust.  To deal with the soot Engineers designed a Diesel Particulate Filter (DPF) that captures the soot.  At some point the DPF can’t hold any more soot.  To get rid of the soot engineers designed a way for the engine’s computer (ECU) to heat the exhaust to 1600F.   The extreme heat acts like a self cleaning oven and incinerates the soot in the DPF.  This self cleaning process is know as “regenerating the DPF” or “regeneration”.

It’s the process of regenerating the DPF that causes so many other problems.   In order to actually get the exhaust that hot the Engineers make the ECU inject a lot of extra diesel fuel into the combustion chamber.  The extra fuel causes the exhaust to get very hot.  Of course it’s not as simple as it sounds.  During regeneration not all of the extra diesel fuel is burned.  Some of the extra fuel washes past the piston rings and into the crankcase oil.  Mercedes calls this “fuel accretion”.  This is obviously not very good for the engine oil.  If you’re using B20 biodiesel it makes the problem much worse.

How and where you drive determines how much diesel fuel will go into your crankcase oil.  If you make short trips in cold weather and shut the engine off before the engine has time to regenerate, expect to have a lot of problems.  The engine never gets hot enough to regenerate the DPF and the oil also never gets hot enough to burn off the condensation that naturally accumulates in the oil.  Freezing temperatures will cause the condensation to freeze.  Until it thaws the frozen water acts like sand in your oil.  Grinding away on sensitive internal engine parts.  Soot is also abrasive.  The more soot in the oil, the more wear you can expect.  Replacing the oil filter every 2500 miles will help remove the soot.  As more diesel fuel washes past the piston rings it causes more crankcase oil vapor to enter the EGR and the DPF.  As the soot builds up in the DPF the ECU ask for more regenerating of the DPF.  That dumps more fuel into the crankcase.  The cycle feeds on itself and keeps making the problem even worse.  Mercedes recommends 3,000 mile oil changes and manual regeneration of the DPF when you’re making short trips in cold weather.  Did your dealer ever recommend this?  For you owners who’s engines have locked up at 40,000 or 50,000 miles, this is the reason.

Mercedes-Benz explains it this way in one of their Service Bulletins.  “The normal regenerating intervals of the BlueTec DPF (the driving distance between two regeneration periods) is 130 miles of City driving, and 320 miles of Highway driving.”   The problem is that very few people only drive in the City or only on the Highway.    “The duration of a regeneration period generally lies between 15 and 25 minutes.” (The regeneration of the DPF takes 15 minutes if you’re on the Highway and 25 minutes in City traffic.)  It takes the engine about 30 minutes to warm-up enough to begin the regeneration.  If you only make short trips in stop & go traffic it can take up to an hour of city driving before you’ll complete a regeneration of the DPF.  Thirty minutes to warm up the engine and another 25 minutes to complete the regeneration.  The colder the weather the longer it will take.   If you shut the engine off before the regeneration is complete all that extra fuel was a complete waste.  You got a load of diesel fuel into your crankcase and nothing to show for it.   If you keep making short trips, you’ll eventually have a crankcase full of diesel fuel and a clogged up DPF.  On the other hand Freeway driving helps the regeneration go more quickly and with less frequency.  If you kick it into passing gear while going up a hill the DPF is in heaven.  Vehicles primarily driven on the Highway in warm weather will have far fewer problems.  This is only a tiny part of what’s actually happening but should help explain why some owners have more trouble than others.  But even with this simplified explanation there are plenty of mitigating factors such as: How old is the ECU software?  What type of oil is used?  When was the oil last changed? Has the Oil Separator been replaced?  How dirty is the air filter?  The list goes on and on.  This is why one owner says he never has any problems and his neighbor is calling a salvage yard.

How can Mercedes-Benz realistically tell every BlueTec diesel owner they can go 20,000 miles between oil changes?  How can they tell every owner to use the same Mobil One 5W/30 ESP oil? According to Mercedes it doesn’t matter where you live or how you drive.  The guy in Chicago who drives 10 minutes to work in January gets the same oil and service intervals as the guy who tows a 7,000 lb. horse trailer through the Rockies when it’s 110F in August.  Mercedes tells everyone to use the same oil and change it every 20,000 miles.

Actually the factory has published many service bulletins about different oil change intervals.  But the Mercedes Marketing Department and Mercedes dealers continue to tell owners they can go 20,000 miles between oil changes. Then the Warranty Department tells dealers the factory will not pay for damage caused by 20,000 mile oil changes.  Every day I get a call from some owner who’s dealer just told them their engine is locked up at 40,000 or 50,000 miles.  The owner says the dealer has never seen this before.  The dealer is very sorry but this is not covered by the warranty.  Hidden away in the back of the Owners Manual Mercedes-Benz says this: “The low temperature characteristics of engine oils can noticeably deteriorate during operation, e.g. from aging, soot and fuel accretion. For this reason, regular oil changes using an approved engine oil from the suitable SAE classification are urgently recommended.”  Would it be asking to much for Mercedes to explain what a “suitable SAE classification” means?  It may come as a shock but most owners don’t study Material Data Sheets for different oil classifications.  Mercedes-Benz knows exactly what it’s doing.  This is intentionally vague and confusing.  When you drive 10,000 or 20,000 miles between oil changes there is a lot of condensation that builds up in the oil.  If you live in a cold climate the condensation will freeze.  When you start the engine the frozen moisture will restrict the oil flow to the crankshaft.  Some people think 10W/60 oil is to thick for cold weather.  The problem is not the viscosity of the oil.  If you have 0W/30 that is full of condensation, it will be just as bad as 10W/60 that is full of condensation.  When both oils are fresh they will still flow at -30 degrees below zero.  It’s frozen moisture that stops them both from flowing.  Mercedes now says to change the oil before cold weather but they don’t explain why.

When the DPF goes through a regeneration cycle, additional diesel fuel mixes with your engine oil.  The fuel dilutes the oil and makes it thinner.    That’s the fuel accretion Mercedes talks about in their bulletins.  If you start with low viscosity 5W/30 oil it becomes very thin when mixed with diesel fuel.  Then the Turbocharger heats the oil to 1600F during the regeneration.  Fuel dilution is nothing new.  The traditional method for dealing with fuel dilution is with heavier viscosity oil. High viscosity 20W/50 or 10W/60 oil is a much better choice for fuel dilution.  Mercedes has actually put this recommendation in their 2018 and 2019 Owner’s Booklet.  However, they explain it in such a convoluted legalistic manner that it’s hard for the average owner to understand what Mercedes is saying. They say different oil viscosity is “urgently recommended” and “severe engine damage can result”.   But they never tell owners exactly what oil they should use.   You’re supposed to do your own research and figure out all of these technical terms.  These new recommendations also apply to all the older OM642 and OM651 BlueTec diesels.  Mercedes expects the owners of older models to search out the newest oil recommendations and get on board.  The owners manual also reminds owners that engine damage caused by the wrong oil is not covered by the warranty.  Mercedes branded oil is 5W/30 and is Mobil One ESP.  If this is not the appropriate oil, why can’t Mercedes tell owners what is the appropriate oil?  Why does Mercedes have to give a disjointed convoluted explanation?

From time to time I’ve mentioned oil Catch Tanks.  Most owners don’t understand them.   And what people don’t understand scares them.  If people actually saw what’s involved in a Catch Tank they would see they are very simple and effective.  A Catch Tank cannot harm the engine.  You could mount it upside down and route the hoses to your radio, and it wouldn’t hurt the engine. Unfortunately no one makes a Catch Tank specifically for a BlueTec diesel.  You have to modify one that was made for a different vehicle.  This makes a Catch Tank something that most owners won’t mess with.  A Catch Tank captures crankcase oil vapor.  The same oil vapor that causes all of the oil sludge in the EGR and air intake system.  Better oil and more frequent oil changes will reduce the oil vapor.  However, if you completely stop the oil vapor from entering the EGR and the air intake system, there is absolutely no question your engine will pollute less and run better. Seriously, the emission system will function as it was designed for the entire life of the vehicle. You will never need to clean the EGR valve or the Swirl Flaps.  No more sludge in the air intake system.  No more oil vapor “poisoning” the DPF.  The DPF won’t need to regenerate as often, and that means less fuel dilution.  However, this is not for everyone. A Catch Tank is for owners with some mechanically aptitude.  You have to open the hood once in a while and drain off the waste oil in the Catch Tank.  There are hundreds of different Catch Tanks on the market.  There is one particular company that makes a really nice one with mounting brackets and hoses that match what’s currently on the engine.  Yes, it cost more than the $29 Catch Tanks on eBay.  No, I haven’t found a cheaper alternative.  Ask your dealer how much they charge for a EGR valve?  Ask them how much it cost to clean the Swirl Flaps?  Ask them how much it cost to replace the clogged DPF and its pressure sensors?  Ask them how much it cost to replace the clogged EGR pipes?  Ask them how much it cost to clean a clogged EGR cooler?  Ask them how much it cost for a blown Turbo?

The factory recommended 5W/30 oil also lacks enough zinc (ZDDP) to protect the timing chain.   The timing chain stretches and you hear a metallic clatter on a cold start.  Now you get to replace a $4,000 timing chain.  If the oil had approximately 1500ppm of zinc (ZDDP) the chain would have lasted the life of the engine.  This is not unique to Mercedes and Diesel engines.  The EPA oil has been ruining timing chains for 25 years.  The EPA claims they are drawing up new oil specs that will require more ZDDP in the oil.  But it hasn’t happened yet.  Some oils do have the proper ZDDP.  Mercedes actually admits to the timing chain failures in Service Bulletin LI05.10-P-049909. And “NO” they won’t pay for the timing chain.

Once your warranty expires the oil vapor will finally becomes visible.    Remove the top cover and you’ll see what appears to be oil leaking from everywhere.   Wait a little longer and the “new and improved” oil cooler seals will start leaking oil.   Then the Heat Exchanger warps and leaks oil. The oil soaked rubber seals in the air intake get so hot they begin to leak air.  Suddenly the engine goes into “Limp Home” because of low boost pressure. The NOx sensors have been updated at least five times.  Yet an oil soaked EGR cooler will cause the new NOx sensors to overheat and fail.  Oil sludge packs the Swirl Flaps and causes the plastic linkage to fail.   All of these problems are solved with better preventive maintenance.  If you think preventive maintenance is expensive, wait until you get the repair bills for cleaning up this mess.

Rust in the fuel system causes injectors to clog and drip fuel which in turn  causes the glow plugs to fail.  When a glow plug fails the DPF regeneration stops.  When the regeneration stops the DPF clogs and the check engine light comes on.  It’s $17,000 to replace the fuel system because of the rust.  Then the glow plugs will need to be replaced.  As the glow plugs are removed they can break off in the cylinder head.  In order to remove the broken glow plug the cylinder head has to be removed and sent to a Machine Shop.  You could have replaced the engine for $35,000 but even that doesn’t include the DPF and fuel system.  Rust in the fuel system is easily preventable.

Mercedes-Benz is constantly updating the software for their computers.   The updates solve all sorts of intermittent problems.   Most of the updates are related to the fuel accretion and DPF regeneration.   Mercedes dealers don’t like doing the updates so they tell owners they aren’t needed or have already been performed.  Owners waste money on expensive repairs that are destine to fail again, and again, simply because the software is obsolete.  Mechanics and owners ignore the software updates because nobody wants to pay for them.    Mercedes admits that all 2009 to 2014 DEF / AdBlue systems will fail.    It’s a known problem with the level sensors and the heating elements.    The list goes on and on.

As of 2019 B20 biodiesel will be sold in every state.   You better start paying close attention to the pump.   At one time, Mercedes did a fair job of explaining the damage caused by B20 biodiesel.   However, Mercedes must have gotten a call from the EPA because Mercedes really toned down their admonitions about B20 biodiesel in their latest sales brochure.  Just so we’re clear on this, Mercedes does not approve any biodiesel above B5.  There are large parts of America where you can only buy B20 biodiesel.  Mercedes will not warranty the damage caused by anything above B5 biodiesel.  So what do you do, when you have no choice?  There are additives you can put in the oil & fuel which will mitigate the damage.  But Mercedes says you can’t use additives in the oil or fuel.  Now what?

I’ve shortened this article because it was getting long and technical.  It’s still to long and technical.  I’ve left a lot out.  Every problem has a solution and a way to prevent the problem.  I get a lot of calls and emails from owners who want more information about how to take care of their BlueTec.   Most Sprinter owners have invested a lot of money in their vehicles.  When SUV owners have problems with theirs they abandon the car.  They just can’t justify the repair cost. Sprinter owners can’t walk away from their investment.

If you’re buying a new Sprinter, you have a once in a lifetime opportunity to properly break in the engine’s piston rings.    The engines come with standard Mobil One ESP synthetic motor oil. Because of fuel dilution BlueTec diesels need to have a perfect seal with their piston rings.  The EPA wanted to reduce the waste oil going into the environment.  So the EPA made everyone stop using the break-in oil for the first 1,000 miles.  If the piston rings have a perfect seal against the cylinder walls, you’ve got a way better chance of keeping fuel accretion to a minimum.   It’s much harder for fuel to get past well sealed piston rings and into the crankcase oil.  You only get one chance on a new engine to get this right.   Plus, it’s simple to do.   But don’t bother asking a dealer to do it.   You’ll just get a big horselaugh and told “you don’t need to do that”.   “Who told you to do that?”   “That’s old school.  Nobody does that any more.”  If you hear those comments, ask them to explain fuel accretion and blow-by in the OM642 diesel?  Ask them to explain Mercedes-Benz service bulletin S-B-09.20/29 and what’s causing the oil to go into the Turbocharger?  Ask them where the oil goes after it enters the Turbo?  The oil is caused by Blow-by on the piston rings. There’s Blow-by at the rings because they were never broken-in properly.  Ask them what’s the purpose of an Oil Separator?  Ask them how many they’ve installed?  Ask them how many times Mercedes has updated the Oil Separator?  Ask them why Mercedes has updated the Oil Separator 14 times?  What’s the problem?

Mercedes-Benz no longer offers factory rebuilt engines for the early versions of the OM648, OM642 and OM651 BlueTec Diesel.  The EPA wants these old engines off the road.  The emissions are way to dirty.   There are currently a number of class action lawsuits over the BlueTec Diesel.   The emission systems are stressed to the limit of technology.  Owners hold out some false hope that these lawsuits will somehow help them.  I hear from so many distressed owners who have been denied warranty on their ruined engine.  They want to know if there is some way to force Mercedes to honor their warranty.  Honestly, there isn’t much hope.  There is only one source for a decent third party rebuilt engine.  Even then, there is more to it than just replacing the engine.  I hear from owners who are so financially upside down that they can’t walk away from their car.  If you’re really stuck, there is only one way to untangle the mess.  It will still cost about $15000, but the repair will last.

I’ve never understood why people would rather fight with Mercedes than change their maintenance routine.  Some people think I’m just trying to drum up business for my shop.  I’ve retired.  It doesn’t matter to me if you service your vehicle at the dealer or do it yourself.  I hear from owners from all over the world.  I doubt the S-class BlueTec owner in Tasmania will drop by very soon.  However, I would like to fund my 2 year old Grandson’s college savings plan.  I have a small window of opportunity to use my experience to help owners and my Grandson.  I’ll explain the preventive maintenance in a way that you will understand.  Once people understand what’s going on they find life with their BlueTec diesel much easier.

If you want help, you can email or call me.  It cost $200 to my Grandson’s college savings plan.  I’ll send you a link to PayPal.  I’ll send you detailed instructions about the problem areas and how to avoid them.  I tell you what to buy and where to get them.   I don’t sell anything.  I don’t have a vested interest in where or how you spend your money.   What I’ve explained in this article is only a small part of the issues surrounding a BlueTec diesel.   I can’t possibly put everything here.   When I send owners the rest of the stuff on this engine they always are stunned by all information.   I’ve had a lot of dealer Mechanics, Service Advisors and Sales people who have ask for help.   They work for Mercedes and have never seen all of the stuff on this engine.  I’ve had a few Sprinter shops ask me to come help them sort out the problems they see in their shops.  On one hand I would like to help.  On the other hand I’m 70 and life is short.  If I could combine several shops into one trip, I might consider it.  I’m defiantly not going where it’s cold.

It doesn’t matter if you have a new Sprinter under warranty or an older model that’s burning a quart of oil every 200 miles.  Nothing I tell you will affect the warranty. I’ve heard of dealers telling owners not to change their oil before 20,000 miles or it will void the warranty.  Tell them to put that in writing on your Repair Order.  There is no way Mercedes can void your warranty because you change your oil every 5,000 miles.  My goal is for you to never need the warranty. Zero warranty claims is a victory.  Success is 200,000 miles on the engine and the emission system still working like new.

If you’re thinking of a new Sprinter, I can explain the best options that are really helpful.  For example; Sprinter offers a auxiliary battery.  You should order that battery because it gives the electrical system the extra voltage it often needs at peak load.  When mechanics scan your diagnostic computers they often find low voltage fault codes.  Even though there is often nothing wrong the low voltage code is still telling you the system voltage is intermittently to low.  It’s better not to have low voltage fault codes.  So just order your Sprinter with the extra battery. That’s actually why Mercedes offers it.  I’ll also tell you what options are a waste of money.  For example, never buy the Prepaid maintenance plan.  They are charging you $600 for a oil change once a year.  The Owners Manual says the engine needs two oil changes.  Mercedes sells this as locking in your maintenance cost so there are no surprises.  The surprise comes when you find out that everything except the one oil change is extra.  I used to think the extended warranty was a smart idea.  But I hear from to many owners who can’t get Mercedes to pay the claims.  I would still recommend all the extended warranty you can buy.  It is transferable to another owner and adds value.  Just be aware that you can’t ignore the maintenance and think Mercedes will pay for your negligence.  When the engine locks up at 75,000 miles, Mercedes will read you the fine print in the back of your Owners Manual.  What it says in the Sales Brochure and what it says in the back of the Owners Manual is not the same.  My goal is for you to never have that discussion.
You can reach me at tom54stephens@gmail.com, or 916.715.0665.