Most people will find this article after they’ve had some major problem with their Mercedes-Benz BlueTec diesel. I also get a lot of calls from people shortly before or after they buy a new Sprinter for their business or as a RV. BlueTec diesels have been around long enough for most interested people to have heard the stories. Owners also know BlueTec diesels are hard to work on and good mechanics are scarce. This is one of those engines that it really helps if the owner knows the basics. You’ll find some information on Owners Forums and YouTube but it’s never the full picture. Nobody explains what caused the problems and how to prevent them. I understand why they don’t give a full explanation because I also struggle to explain this in a concise manner. When I originally wrote this article it was aimed at helping my local customers understand the preventive maintenance that’s unique to a BlueTec diesel engine. I worked for Mercedes-Benz for 50 years as a Mechanic, Shop Foreman, Instructor, Service Manager and a Shop owner. For years I was getting calls for advice from BlueTec owners around the world. After I retired I thought I would just leave the article up to help owners. I assumed the calls would stop, but they increased. As you can tell I’m not a professional writer. As the calls increased I added more information to the article. More calls, more information and more confusion. Clearly I needed a better way of doing this. The basic engine and emission system have remained the same. Mercedes has made improvements to most of the individual parts but that is only half the problem. There are still enough problems to aggravate most owners. After all these years I’m constantly learning something new. The problem is, I kept trying to add everything into the article. I had to clean it up and get back to the basic explanation.
Before I get to much further, I need to give you this disclaimer. This is strictly my opinion. I don’t have any affiliation with Mercedes-Benz or any of their authorized dealers.

I promise to stay focused and avoid jumping up on my soapbox…as often. I get a lot of calls for just one thing. “What’s the best oil or where can I get something I mentioned in the article.” People ask for one thing and that leads to another question and another then another. Depending on your exact situation, there are to many different possible answers. If after reading the article you still have questions, I can answer all of your questions and send you all of the technical information that I’ve saved over the years. It will explain all the aspects of the problems and how to fix and prevent more trouble. I hadn’t planned on spending my retirement answering questions about BlueTec diesels. I get calls from owners who are staring at ridiculous repair bills that won’t permanently solve the problem. Important parts of the correct procedure are left out. The problem is bound to happen again. Often the repair won’t even solve the problem the owner has described.
I’m happy to help you figure out whatever the problem is that you’re having. If you have follow-up questions I will answer them. I have only one 3 year old Grandchild. I really want him to go to college. To help him save for college, I’ll help owners with their BlueTec problems. For a $200 donation to his 529 college savings plan, I’ll answer your questions and send you more technical information then you can possibly imagine. I know Dealers and repair shops struggle to understand this engine because I hear from them all the time. Owners have to be involved in the maintenance or you’ll pay dearly for not understanding how this engine works. If after reading this you want more help, email me at tom54stephens@gmail.com. You can also call me at 916.715.0665.

Mercedes-Benz introduced the OM642 V6 BlueTec diesel in 2007. A few years later they introduced the OM651 4 cylinder BlueTec diesel. BlueTec refers to the type of emission system. The early versions did not have the AdBlue or what’s also referred to as the DEF (Diesel Exhaust Fluid) system. Other than the DEF, they operate the same way. Frequent updates to the parts have improved the reliability. There is however one thing that has never changed and it starts most of the trouble. Mercedes has used the same Mobil One ESP engine oil since 2007. It was bad in 2007 and it’s still bad today. This is hard for most owners to understand. Why would Mercedes and Exxon Mobil use an inferior oil in the engine? Who am I to question this oil in this engine? The oil problem is such a continuous matter that I’ve put the oil information into its own article on this website. It will explain the problems with the oil. Briefly, the oil is not designed for an exhaust driven Turbocharged BlueTec diesel. This oil was not designed for extremely high oil temperatures and extreme fuel accretion. Toss in 20,000 mile oil changes and I’m amazed the engines don’t lock-up sooner. The oil quickly breaks down and turns into sludge. The sludge causes a cascade of problems throughout the emission system. The oil article explains all of this and shows the proof in the 2019 Sprinter Owners manual and the Exxon Mobil Product Data website. As per the 2019 Sprinter Owners manual, the correct oil must have the appropriate ACEA or API certifications for a Turbocharged BlueTec diesel. The correct API approval is “CK-4”. The correct ACEA approval is “E9” or “C5”. As per Mercedes, one or the other must be on the label. These are the highest approvals a diesel oil can have. You will not find these approvals on the Mobil One 5W/30 ESP or the Mercedes-Benz branded oil. The wrong oil causes most of the trouble. If you don’t believe it, call Mobil at 1.800.275.6624. You can call Mercedes at 1.800.FOR.MERC. Ask them exactly this question. “Does the ACEA or API approve Mobil One 5W/30 ESP or the Mercedes-Benz branded 5W/30 oil for the OM642 BlueTec diesel?” “Do these oils meet the Mercedes-Benz New Vehicle Limited Warranty requirements published in the 2019 Sprinter Owners Manual for a OM642 BlueTec diesel?” The answer is “no”, but call them and you can hear it from them. If they say “yes”, ask them if they will put that in writing? I explain this in the article about diesel oil.

The problems begin when the Diesel Particulate Filter (DPF) regenerates. The DPF is in the exhaust and it traps the black soot that’s in a diesel exhaust. Pressure sensors tell the engine computer (ECU) that the DPF needs to clean out the soot. To do that, the DPF has to heat up to 1300F. To get that heat, the ECU injects extra fuel into the combustion chamber. But not all of that extra fuel is burnt. Some washes past the Piston Rings and goes into the crankcase oil. Mercedes calls this “fuel accretion” or “fuel dilution”. If you drive in slow moving city traffic in cold weather, the DPF has a hard time burning off the soot. It can take up to one hour for the regeneration cycle to complete in those conditions. If you shut off the engine while the DPF is regenerating, the ECU injected a bunch of extra fuel but didn’t burn off the soot. The ECU will try again the next time you start the engine and drive for about a hour. If you shut it off again before it’s done burning off the soot, the crankcase oil gets another dose of diesel fuel into the oil. When the ECU heats up the DPF it also heats the exhaust gases that are turning your Garrett Turbocharger. Those exhaust gases will heat the Turbo to over 1600F. Your engine oil also lubricates the Turbo. That means your engine oil is exposed to extremely high temperatures. This oil also has diesel fuel mixed with it. The oil gets so hot that it vaporizes. By law this hot oil vapor cannot vent to the atmosphere. It has to be controlled by a “Crankcase Ventilation System”. It’s also known as a PCV valve or a Oil Separator. Ideally, the hot oil vapor should be condensed and returned to the crankcase as a liquid. In the OM642 diesel the oil gets so hot that it doesn’t have time to cool down. The hot oil vapor leaves the engine via the Oil Separator (PCV). The vapor travels through a hose that’s connected to the air intake of the Turbocharger. The oil vapor is sucked into a Turbocharger that is glowing red hot. The Turbo is so hot the oil vapor doesn’t have any chance of cooling off. The vapor goes through the Turbo and into the Intercooler. The Intercooler’s job is to cool down the hot air from the Turbo before it goes into the combustion chamber. As it goes to the combustion chamber it passes through the Intake Manifold and Swirl Flaps. The air going into your Intercooler has a lot of oil vapor mixed with it. Over time, the Intercooler fills with oil sludge that restricts its ability to cool the air. Turbochargers get very hot from the exhaust gas going through them. Your Garrett Turbo and Intercooler are cooled by the air flow around them. There are water-cooled Turbochargers and water-cooled Intercoolers that control the cooling of these components much better than what’s currently on the OM642 diesel. Mercedes chose to put the cheapest Turbo and Intercooler on your engine. The extreme heat created by the Turbo is at the heart of the problems. The rubber hoses, seals and plastic parts in the Intercooler system were not designed for the extreme heat and oil sludge. Even the Turbo had to be redesigned. The extreme heat shatters the Turbo. The new Turbo is still not water cooled. However it was made with thicker metal which Garrett appropriately calls “Sever Duty”. The oil vapor rots the rubber hoses and seals. The heat cracks and melts the plastic. This causes air leaks which cause “low Boost” fault codes and Limp Home power loss. As the oil vapor air enters the Swirl Flaps they also become clogged with sludge. The Swirl Flaps have movable flaps that were designed to give the engine more power. The flaps are controlled with plastic linkage which finally fails and causes the engine to go into the Limp Home mode. The plastic parts have been updated to metal, but it’s a major job to replace the broken plastic. You’ll have to remove other parts to get at the Swirl Flaps and those parts often need to be replaced when they’re disturbed. It’s this sort of thing that drives the repair cost so high. If you address the fundamental problems before they cause all of these other problems it cost much less to maintain. The hot oil vapor also passes through the EGR (Exhaust Gas Recirculation) valve and the EGR Cooler. The EGR finally clogs with the burnt oil sludge and triggers a Check Engine Light (CEL). When the EGR Cooler clogs with oil sludge it causes the exhaust temperature to go to high. That causes even more Blow-by. The extreme heat causes the NOx and other exhaust sensors to fail. It even causes the exhaust pipes to crack and cause exhaust leaks into the cabin. If you have exhaust leaks that nobody can seem to find, send me a email and I will send you pictures of where they leak. This is a obvious safety issue and I don’t charge for helping with exhaust leaks. Just send me an email. All of these high exhaust temperature failures are telling you to clean the EGR Cooler. As the oily exhaust finally tries to exit the engine, but it’s stopped by the DPF. Instead of soot, the DPF becomes clogged with oil sludge. The pressure sensors see the oil sludge as a restriction and ask the ECU to increase the exhaust temperature. The whole process repeats itself and it becomes a downward spiral.

So, what has Mercedes done to correct these problems? Around 2013 Mercedes increased to oil capacity from 8.5 quarts to 13 quarts of oil. More oil is a big help. It would help even more if they used the right oil. When Mercedes went to the larger oil pans they also improved most of the other parts in the engine and emission system. There’s a lot of information about the changes Mercedes made when they went from the 8.5 to 13 quart engines. I’ll touch on a few of the most important in a moment. These changes are some of the information I send people who want more. Most of the time, repair cost are so high on the 8.5 engines that owners are forced to delete the emission system. The 13 quart engines can be cleaned and updated. They can still use their emission systems. These are the details I send to owners when they want to know a lot more about what’s causing their specific problems.
Mercedes engineers have tried many times to slow down the amount of oil leaving the crankcase. They have redesigned the Oil Separator (PCV valve) at least 14 times. More importantly Mercedes has also redesigned the software in the ECU. Software updates correct Fault Code errors and reduce the amount of fuel accretion when the DPF regenerates. Most Mercedes dealers refuse to do the software updates for several reasons. They tell owners the updates have already been done or they aren’t needed. Unfortunately the emission system will never work right until the software is updated. This is a continual process. Mercedes is constantly sending out updates to the ECU. Even new Sprinters have updates for their software. However, the basic software is much better than older models.
The only way owners can physically stop the oil vapor from going into the Turbo is with a Catch Tank or it’s sometimes called a Catch Can. A Catch Tank captures the oil vapor before it can enter the Turbo. It holds the oil vapor in a tank to be periodically drained off. No one makes a Catch Tank for the BlueTec diesel. There is one that’s made for another type of Diesel engine and it works fine. You can’t use a Catch Tank that’s to small for this engine or you will have oil leaks. Speaking of oil leaks. This engine has a number of known oil leaks. The root cause of the leaks is excessive crankcase pressure. Blow-by at the Piston Rings causes the crankcase pressure. Stop the Blow-by and you’ll stop the oil leaks. The oil also causes the timing chains to stretch. Timing chains are another known problem on this engine. 20,000 mile oil changes allow to much soot to build up in the oil. Soot is very abrasive and wears the Timing Chain. Soot is what turns diesel oil black. Zinc is also an important part of motor oil. Mobil One ESP only has half the zinc that is generally considered the proper amount for the Timing Chain. If you hear a metallic clatter on a cold start that goes away after a few seconds, that means the timing chain needs to be replaced.
Dirty air filters cause the crankcase pressure to go much higher than a gas engine. Replace the air filters every 20,000 miles.
Never let the engine idle for long periods. When Sprinters are used as Delivery Vans, Limo’s or Ambulance’s they often let their engines idle for long periods. They have the highest Turbo failure rate. When Turbo’s fail, you must remove the Intercooler and clean out the broken parts.
The oil sludge is very difficult to clean. Once the engine is routinely switching on the Check Engine Light the owner is practically forced to clean up the oil sludge in the EGR and other systems. At the same time, the typical BlueTec is also struggling with the other common problems. This gets to be very expensive and frustrating. Not to long ago cleaning the Intake system meant your mechanic had to disassemble a lot of the engine. There is now a special tool for pressure cleaning the oil sludge that’s caked in the Swirl Flaps and the EGR. There are now adapters made specifically for the OM642 and the OM651. The tool can also be used for pressure cleaning the DPF. These are the things that will save owners thousands in repair cost and down time. This also increases the resale value far more than what they cost to install. Wouldn’t you pay more for a used Sprinter when the owner clearly took better care of it?

Mercedes loves its acronyms. The AdBlue system is also called the SCR (Selective Catalytic Reduction) or the DEF (Diesel Exhaust Fluid) system. They are all the same system. AdBlue is the special DEF that you keep adding to the tank. All the DEF tank internal parts on the 8.5 engines will fail. Some of the early 13 quart engines will also fail. Mercedes has extended the warranty to 8 years or 80,000 miles. It’s the heating elements and level senders that fail. Always keep the tank full. Don’t wait until the low level light comes on. The DEF freezes at 12F. The DEF has to thaw out in 17 minutes and begin to inject the DEF into the exhaust. People in cold climates will have more trouble with this system. There is an aftermarket kit that has a larger heating element. It’s not so important if you live where it’s above 12F. If you live where it gets below 12F use the aftermarket tank kit. There is also a device for reseting the starter lockout if the AdBlue system fails and you’re on a trip. Mercedes also makes an Auxiliary battery kit for all the Sprinters. These vehicles have so many computers that one battery can’t supply enough voltage at peek load. The special battery kit Mercedes makes for the Sprinter will give the computers enough voltage when demand is the highest. Low Voltage fault codes are quite common. The computers need 12.5 volts to operate properly.
Mercedes also makes a block heater for cold climates. It’s important to keep condensation from freezing in the oil.
Fuel system contamination is another problem. The typical complaint goes like this. The owner comes to a stop light and the engine intermittently dies. It restarts right away, but the CEL comes on after starting. The vehicle may or may not be covered by the warranty. One of two things will happen. There are often Fuel Rail fault codes. The dealer looks at the fault codes and starts replacing parts. The problem isn’t fixed and the customer returns. At some point the dealer checks the fuel system and finds tiny specks of metal in the fuel system. Metal in the fuel is often caused by contaminated fuel. Gas or water is the most common. Even if they don’t find any contamination in the fuel, they will blame it on the fuel and there is no warranty. If they find metal in the fuel, you just bought a $17,000 fuel system repair. The bottom line is, you’re on your own when it comes to the fuel system. There are several easy ways to protect the fuel system. Another option is to contact your insurance and get coverage for damage caused by contaminated fuel. Make sure you get “Stated Value” for the damage. There is no cheap way to repair the fuel system.

NEW SPRINTERS WITH THE OM642 DIESEL:
People read about all the problems with BlueTec Sprinters and they get scared off from buying one. The new Sprinters are actually very nice vehicles. They really hold their resale value, so you can justify the preventive maintenance cost. Mercedes has improved many things. If owners follow some simple maintenance guidelines they will have a great vehicle. One of the most important things you can do to a new Sprinter is start the engine off with Break-in oil. Break-in oil lets the Piston Rings form a perfect seal with the cylinder walls. This greatly reduces the Fuel Accretion that gets into the engine oil. You only get one chance for the Piston Rings to form a perfect seal. I get calls all the time from owners who say they wish they had read about this before they started driving. If you are still at 1,000 or 2,000 miles, you can still run the Break-in oil for 500 miles and get some benefit.