June 17, 2021 — The following comments are my own opinions.  After 50 years working with and for Mercedes-Benz as a Mechanic, Shop Foreman, Instructor, Service Manager and Shop Owner I retired in 2018.  I no longer have any affiliation with Mercedes-Benz or its authorized dealers. 

I started this article about 10 years ago. In the beginning is was just my way of explaining the BlueTEC diesel and the unusual problems we were starting to see. Over time I started to hear from BlueTEC owners from around the world. How could I possibly be the only person trying to explain the BlueTEC? When I look back on those days they seem so simple. The original technical manuals from Mercedes made the BlueTEC sound so easy. Even now after all the negative publicity about their emissions fraud, it is still very hard for many owners to find help. I’m constantly hearing from owners who are stuck at a dealer who can’t diagnose common problems. The OM642 and OM651 diesels still operate the same as they always have. Mercedes has fixed most of the mechanical problems and the 907 Sprinter is much better. The problem is, BlueTEC’s are to complicated for most owners and dealers. After all these years, many owners still think the BlueTEC diesel is somehow just like the older diesels. There’s not a day goes by that I don’t hear from an owner with some problem their dealer can’t figure out. I wish I could say I’m surprised, but it’s the same story over and over. 

I’m sure you’ve noticed all the websites popping up with the BlueTEC complaints. They talk about the symptoms, but not the actual cause or how to prevent the problem in the first place. I’m a big believer in proactive preventive maintenance and education. Unlike other types of engines, BlueTEC owners have to understand how the BlueTEC emission system operates. Unfortunately Mercedes doesn’t make it easy for owners. The Owner’s Manual doesn’t address the most important technical questions. Instead, Mercedes tells its dealers to explain things like fuel dilution, the SCR system and the DPF regeneration. But dealers don’t have time or the manpower. Mercedes should at least include this information in the Owner’s Manual.

I recently spoke with a new owner who just spent $250,000 for a spectacular BlueTEC Sprinter RV. The RV Salesman spent hours explaining the coach and how it works. But when it came to the engine and emission system maintenance, see your Mercedes-Benz dealer. When the owner went to the Mercedes dealership, he got ten minutes with whoever wasn’t busy. He didn’t buy his new RV from the Mercedes dealer, so they don’t see him as their customer. He’ll go there for warranty repairs and maybe a few oil changes. The real profit was made by the RV company. This machine operates on public highways. This is not a vehicle where you can turn the key and drive. People really need to understand how this engine and emission system works. It can leave an uninformed driver setting in the middle of the road. Owners have a right to easily understood technical information.

DPF Monitor: I’ve asked hundreds of the new 907 Sprinter owners if their Salesman explained anything about the operation of the DPF monitor? Not one owner has ever told me their Salesman or Service Advisor ever explained the DPF monitor. As of model year 2019, the 907 Sprinter has a DPF Monitor built into the Instrument Cluster. All BlueTEC diesels have a DPF (Diesel Particulate Filter) in the exhaust system. The DPF captures the black soot in the diesel exhaust. When the DPF is finally full of soot the emission system automatically increases the exhaust temperature to 1500F to burn off the soot. Much like a self cleaning oven. Mercedes calls this the DPF regeneration. The DPF typically regenerates every 300 to 400 miles. The regeneration cycle normally takes 15 to 25 minutes. It’s the extreme heat required for the DPF regeneration that causes most of the other problems. To be more specific, it’s the interruption of the DPF regeneration heat cycle that’s the root cause of most of the trouble. For years, Mercedes told everyone the DPF regeneration is automatic. They’ve given owners the impression there is nothing for the driver to do. In reality, there’s lots for owners to understand about this process. If the driver knows when the DPF is regenerating, they can prevent the fuel dilution. The fewer times the DPF regenerates, the better it is for the life of the engine. There are lots of things the owner can do to reduce the workload for the DPF. Better oil, frequent oil changes, a new PCV valve, a Catch Tank, a fresh air filter are all things that will keep oil sludge out of the DPF.

In order to understand the DPF regeneration, first you need to know when it comes on. Mercedes now offers a DPF monitor (p/n: 906.900.34.04) for the 2008 to 2018 BlueTEC Sprinters. As of 2019, a DPF monitor is built in at the factory. But before you get to excited, Mercedes still doesn’t educate owners about the DPF regeneration. In fact, Mercedes has gone out of its way to obscure the information. Most dealers don’t even know Mercedes makes a DPF Monitor.  Ask your dealer to explain the DPF monitor? Ask them what things interrupt the regeneration? Ask them for any written instructions that explain the DPF monitor? I’ve written the complete instructions for both versions of the DPF monitor. I explain everything that interrupts the regeneration and what happens. It includes all the fault codes and Service Bulletins pertaining to everything related to the DPF. It also includes all the ways you can extend the distance between regenerations and how to reduce the exhaust temperatures.
Note: The Emissions Recall on the 2009 to 2016 BlueTEC diesels includes a new Instrument Cluster for the SUVs and passenger cars. The new Instrument Clusters will have a built-in DPF monitor like the newest 907 model Sprinters. The 906 BlueTEC Sprinters will still need the Mercedes DPF monitor, p/n: 906.900.34.04. 

Update: On 3/17/2021 Mercedes-Benz and the DOJ reached a final agreement in the diesel emissions fraud settlement. Mercedes will notify owners when it’s their turn for updated parts. There are slight differences between model years 2009 to 2016. Generally speaking, Mercedes will replace the NOx sensors, the SCR Catalyst, the Dosing valve, the CDI software and a new Instrument Cluster in the passenger cars and SUVs. Mercedes will extend the warranty on a few other emission parts. Mercedes can also resume selling BlueTEC diesels. Go to https://BlueTechUpdate.mbvans.com or call 1.833.841.9362 for specific information about your vehicle.
The emissions recall is actually a good deal. It’s a little confusing. Mercedes said they would replace the Instrument Cluster but no one is actually getting a new Instrument Cluster. Dealers don’t seem to know why. Originally Mercedes said they would reimburse owners for recall repairs they had paid for, but now they won’t. Mercedes is giving owners who get the recall $3590 cash back. For some owners this is fair. For other owners this is to little and way to late. The recall fixes problems with the NOx issues. Many owners think that fixes all the problems. It doesn’t. The DPF or the soot part of the emission system is not addressed. Mercedes needs to explained the problems with the DPF regeneration and all the updates to make the DPF operate properly. If owners spent the cash back on the DPF side of the emission system, they would have a very reliable system. In my opinion, Mercedes is intentionally down playing the DPF operation because they know this is their biggest problem. They know the DPF operation is so complicated most people would never buy a BlueTEC if they knew what they were getting into. One owner recently sent me copies of his latest BlueTEC Sprinter repair orders. The dealer is one of Mercedes biggest Sprinter dealers in America. The Service Advisor wrote on one repair order this was the 50th time the Van had been into the shop for a lack of power. The repair order said the DPF keeps clogging. The DPF was replaced several times. The engine had also been replaced. And here it was again. The owner contacted me asking for help. In the 50 comebacks, no one ever told the owner about the DPF monitor. No one ever told the owner what canceled the DPF regeneration or the consequences of canceling the regeneration. In fairness to the dealer, Mercedes never told their own mechanics everything about the DPF regeneration. I looked back through the BlueTEC Product Introduction manuals Mercedes gives mechanics when a new system comes out. Mercedes never gave mechanics all the details about the DPF regeneration. Mercedes told everyone the regeneration was automatic and would go unnoticed by the owner. I sent the owner a complete description of how the DPF system works and how to use the Mercedes-Benz DPF monitor. After I explained the entire DPF operation he understood why his DPF kept clogging. He didn’t need a new engine and all the previous 50 repairs. He needed a DPF monitor and a 15 minute explanation. Even though Mercedes is now installing a DPF monitor in the Instrument Cluster, they still don’t explain its operation.
When I saw the repair order with 50 comebacks I can’t imagine a Service Advisor writing that. You would think that would blow the roof off the Service Department. I know this dealership and they have at least 5 Shop Foreman, 65 Sprinter mechanics, 3 Service Managers and a dozen Service Advisors. I can’t fathom 50 comebacks for one customer? If I hadn’t seen the repair order I wouldn’t believe it. And they still didn’t tell the poor guy about the DPF monitor. When he asked them about it, they said they had never heard of it.

CHECK ENGINE LIGHT (CEL): I recently had an owner contact me after they had a CEL while on a 3,000 mile trip. They called their Mercedes-Benz dealer when the CEL first came on. They were still 1,500 miles from home. The engine still felt like it was running normal. Their dealer told them to continue driving with the CEL on. WRONG! The wife didn’t feel comfortable with this and she found this article. She called me for my opinion. Whenever the CEL comes on for ANY reason, the DPF will NOT regenerate. As you drive the DPF continues to fill with soot. Once the DPF is clogged with soot, the engine quits running. You don’t have any way of really knowing how far you can drive before the engine will quit. You might go 10 miles or 1,000 miles. If it’s covered by the warranty, make Mercedes pay for towing it to the closest dealer. NEVER ignore a CEL. Get to a qualified repair shop ASAP and get it checked. BlueTEC diesels are not like a Gas engines. You still shouldn’t ignore a CEL on a Gas engine, but many people have driven for years with a CEL on. You can’t do that with a BlueTEC. And find a new dealer.

–  Timing Chain: Mercedes admits the Timing Chain stretches a lot faster than it should.  (See Service Bulletins LI05.10-N-057796 and LI05.10-P-049909).  Mercedes has redesigned the chain and sprockets for the third time.  In reality, it’s the oil and excessive soot suspended in the oil that’s causing the Timing Chain and sprockets to wear so quickly.  The original Timing Chain and sprockets would last indefinitely with higher quality oil, better oil filtration and 5,000 mile changes. Timing Chains can start clattering on cold starts as soon as 40,000 miles. Short trips with frequent interruptions in the DPF regeneration causes high fuel dilution. Timing Chains don’t do well with oil mixed with diesel fuel. Some Timing Chains can make it past 180,000 miles with better oil changes and less fuel dilution. Once again, this is one of the anomalies specific to each individual BlueTEC diesel and its unique operating conditions. Using the factory recommended oil and the factory recommended service intervals, by 80,000 miles the average BlueTEC Timing Chain is very close to its wear limit. 

As the Timing Chain stretches it changes the Camshaft Timing.  This causes a significant increase in NOx emissions and a noticeable drop in performance. When new, the Camshaft timing is at TDC or zero degrees at the crankshaft.  As the chain stretches, the Crankshaft timing advances to its wear limit of 11 degrees. Mercedes offers an official method to measure the amount of chain stretch for both the OM642 (see AR05.10-P-7600GZB) and the OM651 (see LI05.10-N-057796). It typically cost $500 or $600 for the test. If you know where to look, it doesn’t cost anything to get a close approximation of the OM642 chain stretch. Remove the oil cap and look straight down at the piston in the Chain Tensioner. When new, the Chain Tensioner piston extends about 5mm from the body of the Chain Tensioner. When the piston extends about 13mm, the Timing Chain is at its wear limit. Let’s say you look at your’s and the piston is extended about 10mm. What’s your plan? 

Mercedes makes it sound like you can roll in a new OM642 Timing Chain for about $3,500. But that’s not the whole story. As these engines get to higher mileages, lots of things can go wrong. Plus $3,500 doesn’t include removing the front cover and replacing the sprockets. If you remove the front cover you better replace the Oil Filter housing and the Oil Pump. If the Oil Cooler and Swirl Flaps have never been addressed, now’s the time. The Heat Exchanger is also a known problem (see LI18.30-P-059712 and LI18.30-N-056338), so it will need to be replaced. Take shortcuts and the odds of an engine failure go way up. Doing the repair properly can cost $6,000 for the OM642. If you own the OM651, you can double the repair cost. Back to the original question. If your engine has over 80,000 miles, you can assume the Timing Chain is getting close to its wear limit. You could drive until the Timing Chain breaks and buy a new engine. You can sell it and maybe take a loss. Or you can switch to a different type of oil and install a Catch Tank. A few years ago, I suggested owners could save the cost of replacing the Timing Chain by switching to a special motorcycle oil with the API “CF” diesel approval.  The specific type of motorcycle oil is a Group 5 Ester synthetic. Various Owner’s Forums had a cow. Motorcycle oil in a BlueTEC diesel? You’ll kill everyone within a 20 mile blast radius. Your BlueTEC will be radioactive waste site for 500,000 years.

I still stand by that opinion and I feel vindicated by recent BlueTEC oil developments in Europe. Group 5 Ester synthetic oils are now available with the API “CF” and MB229.52 approval. In fact, that’s the type of oil Mercedes dealers in Germany are using. Group 5 Ester synthetic is naturally low in Ash. Even though these Group 5 Ester synthetic oils have the MB229.52 approval, for some reason they are not listed on Mercedes “Bevo” website of approved oils. BlueTEC diesels are prone to bore glazing. Ester synthetic motorcycle oil has fewer friction modifiers to prevent bore glazing. BlueTEC diesels are also prone to fuel dilution. Ester synthetic motorcycle oil with the API “CF” approval is specifically designed to withstand high fuel dilution. Ester synthetic motorcycle oil has twice as much zinc as the factory oil. Zinc protects the Timing Chain. You can stick with the factory 5W/30 ESP oil and wait until you hear the Timing Chain clatter on cold starts. Or you can preemptively use a different oil. Once you hear the clatter, the Timing Chain is shot. If there’s a cheaper or better way to avoid replacing a high mileage Timing Chain I would like to hear it?

Fuel Dilution: None of the 2007 to 2018 BlueTEC diesels have a DPF monitor. There is no way for the driver to know if the DPF is regenerating. Mercedes Service Bulletin LI18.00-N-054809 explains how interrupting the DPF regeneration causes fuel dilution. Every time the DPF regeneration is interrupted, unburnt diesel fuel washes past the piston rings and into the crankcase oil. On top of this, Mercedes tells owners the only thing that interrupts the DPF regeneration is shutting off the engine while the DPF is regenerating. But this is not true. There are many things that will interrupt the regeneration. When any one of a dozen intermittent things interrupts the DPF regeneration, raw diesel fuel washes into the engine oil. Mercedes Service Bulletin GI01.10-P-056315 explains what happens when this mixture of engine oil and diesel fuel gets hot. The crankcase oil turns into something resembling black jello. Mercedes calls it “oxidation”. The engine is ruined.
The Turbocharger is built by Garrett. Mercedes chose not to use Garrett’s water cooled Turbocharger. The job of cooling the Turbo falls to the engine oil. When you’re driving in the mountains or the DPF is regenerating, the Turbocharger operates at 1600F. As a result, Mercedes published Service Bulletins LI09.40-N-063089 and LI09.40-P-054329. The Turbocharger starves for oil because the extreme heat causes oil coking in the oil galleys. Mercedes redesigned the Turbo’s pedestal twice.
If you can avoid interrupting the DPF regeneration, you’ll have less diesel fuel in the engine oil. But if you own a 2007 to 2018 BlueTEC, there’s no way for you to know when the DPF is regenerating or if the regeneration is interrupted. Since Mercedes forgot to explain any of this in your Owner’s Manual, they published Service Bulletin LI18.00-N-054809. The bulletin ask your dealer to personally explain the problems caused by fuel dilution. Mercedes does mention this in your Owner’s Manual, but they don’t call it “fuel dilution”. Mercedes calls it “fuel accretion” in your Owner’s Manual. I’ll let you speculate as to why they use that description? They do say, “As a result, fuel may accumulate in the engine oil and cause engine failure”. Mercedes is quite concerned and the bulletin should help your dealer clarify this problem. This is by far the most common reason for a BlueTEC engine failure, so you might want to ask your dealer about this.
A better solution is to prevent fuel dilution before it happens. In 2019 Mercedes offered their own DPF Monitor, p/n: 906.900.34.04 for the 2007 to 2018 BlueTEC diesels. It’s the only way you can actually know when the DPF is regenerating and how to avoid interrupting the DPF regeneration. The operating instructions are a little vague, so I’ve rewritten them to explain all the situations that will interrupt the regeneration. Mercedes doesn’t offer any instructions for the 2019, 2020 and 2021 DPF monitor, so I wrote directions for its operation.

Engines with worn Timing Chains are often burning oil.  BlueTECs burn oil because the piston rings are packed with burnt oil and the Cylinder Walls are Glazed.  The piston rings are stuck in their ring grooves. The piston rings can’t press tightly enough against the polished cylinder walls.  High detergent flushing oils can free-up the piston rings. Special fuel additives can slowly remove the burnt varnish on the cylinder walls.  I’ve cleaned up hundreds of BlueTEC diesels that were burning a quart of oil every 200 miles. Persistence and proven methods will bring a BlueTEC back from the brink, but only if the Timing Chain hasn’t stretched beyond its wear limit. If the engine has high oil consumption and the chain is slapping on cold starts — there’s bound to be to many ancelerry problems. I’m afraid the party is over.

–  BlueTEC diesels and “Direct Injection” (DI):  There’s a very good YouTube video explaining DI.  “Direct Injection, Problems and Solutions | The Fine Print” – https://www.youtube.com/watch?v=xrLNDgrIw3U&t=90s. This video will really help you understand how the basic problems begin.

–  AdBlue, DEF, SCR (Selective Catalytic Reduction) and NOx sensors:  This is the area covered by the fraud recall.  SCR and DEF are used to reduce NOx.  The SCR has several sub-categories which need their own detailed explanations.  Owners have problems with one part of the system and they hope they can limit the repairs to that one area.  The most common problems are with the AdBlue tank and the NOx sensors.  This is the system that causes the “No Start” countdown.  It’s also the most common cause of the “Limp Home” loss of power mode.  Once again, it’s simpler to prevent the problem then it is to dig out of the hole.  Even though Mercedes has admitted that all the early AdBlue tanks will fail, I’ve shown lots of owners how to prevent the failure. 
1. Keep the tank full. 
2. Use genuine Mercedes AdBlue. 
3. Flush the tank every 2 years. 
4. Clean the Dosing valve every 40,000 miles. 
5. Reduce the exhaust temperatures.  Mercedes has updated the NOx sensors 5 times. Mercedes says they will replace them as part of the fraud recall.  But extreme heat is the main cause of NOx sensor failures.  The extreme heat is caused by oil sludge in the EGR Cooler and the Intercooler. The Differential Pressure Sensor causes the DPF to regenerate too often. Software updates are also critical to lowering the exhaust temperatures. All of these things work as a system.

Mercedes is now fixing some of these things as part of the recall. While Mercedes has updated and modified virtually every part in the engine and emission system, that doesn’t mean they will replace everything.  Far from it. The frustration for most owners is that no one at Mercedes will explain what’s wrong with the entire system. It would be very helpful if Mercedes spelled out everything that needs to be updated on every year and model. A to Z. The information is now available, but it’s all mixed up. It’s not in a concise orderly format. Instead of giving the owner a complete picture of the entire situation, dealers fix things one by one as they break. They fix the symptom but not the cause.  

–  The DPS (Differential Pressure Sensor): The DPS tells the CDI computer when the DPF is full of soot and it’s time to start the automatic regeneration.  Over time, the DPS gradually tells the CDI computer to regenerate the DPF more frequently than it should.  This is a big part of what causing so much of the extreme heat.  Over the years this has been one of the hardest problems to thoroughly understand. Mercedes published many service bulletins about the DPS. But no single bulletin explained the complete problem. The DPS affects other parts of the system that aren’t so obvious. For years no one had any idea this is where the problem originated.  Even now, it’s not as simple as just replacing the DPS. Most experienced Mercedes mechanics think this matter is solved as of 2016. But it appears model years 2017 and 2018 may also experience problems with the DPS.  From the many owners I’ve talked to, there’re plenty of dealers who still don’t understand this part of the system.  This happens so slowly people think they’ll wait until they see a problem.  If you wait until you notice the problem, you’ll have missed your opportunity.

–  Exhaust fumes entering the cabin:  People smell exhaust fumes and ask their dealer to take a look.  Normally the dealer says they don’t see any exhaust leaks.  This is another known problem where Mercedes has published many Service Bulletins about exhaust leaks.  The extreme heat caused by the DPF regeneration will crack the welds in the exhaust.  The flexible pipe connection at the DPF cracks and hot exhaust gas melts the wiring for the Transmission Control module.  The wiring shorts out and you come to a sudden stop.  If the Transmission Control module shorts out it will cost you $2,000 to $3,000…. if you’re still alive.  There’s an easy way to prevent this.  

The extreme heat causes the bracket holding the DPF to eventually break.  The DPF falls onto the road and give the people following you a gift they will never forget.  The Bracket is attached to the Bell Housing of the transmission.  When the bracket breaks it rips a hole in the Bell housing.  The $40 Bracket has been updated twice.  Did your dealer did tell you about the bracket or are they waiting for this $6,000 repair to make their month?  See Service Bulletin LI49.10-N-067486.

– 4×4 Problems 907 Sprinter: Intermittent problems with the Four Wheel drive won’t engage or quits working. Some owners notice a loud grinding noise. See Service Bulletin LI28.19-N-071366 for software update.

–  Oil leaks:  Oil leaks are well known on the OM642 V6 BlueTEC.  The oil cooler is the most famous leak.  The oil cooler is no longer a problem on the newer models, but there are about a dozen other known leaks.  Oil leaks are caused by excessive crankcase pressure from blow-by at the piston rings.  Some leaks are cheap to fix and others are very expensive.  I’ve put together a pdf file with every known oil leak and the cheapest way to fix them. Understanding and stopping blow-by at the piston rings prevents a long list of chronic BlueTEC problems.  

–  Fuel system problems:  The BlueTEC fuel system has two low pressure delivery pumps located inside the fuel tank.  Fuel is pumped through the fuel filter and into a High Pressure Fuel pump (HPFP).  The HPFP increases the fuel pressure to 23,000 psi.  From there, fuel goes into the fuel rails and injectors.  BlueTEC fuel systems typically fail because the diesel fuel was contaminated with gasoline or water.  Diesel fuel must have at least 15 ppm of sulfur. Sulfur is the lubricant in diesel fuel. Diesel fuel with less than 15 ppm of sulfur can also cause low fuel rail pressure. Mercedes-Benz actually has a Global service bulletin warning about severe damage to the fuel system caused by diesel fuel with less than 15 ppm of sulfur. You may notice intermittent dieing, CEL, lack of power, surging, hard starting or a drop in fuel economy. Driving with #2 diesel fuel (Summer blend) into freezing weather can cause these same symptoms. Mercedes has updated the fuel filter 5 times. To avoid problems, change the fuel filter every 20,000 miles with a genuine Mercedes fuel filter as per your VIN. Whatever the cause, tiny flakes of metal from a damaged HPFP will contaminate the fuel rails and injectors. The fuel filter does not protect the fuel rails and injectors from metal contamination caused by the HPFP. That’s all it takes and you’re looking at $17,000 to replace the fuel system.  You may think you have some warranty coverage, but the odds of Mercedes warranting any BlueTEC fuel system failure is virtually zero. Feel free to verify this with your dealer.  However, there are simple prophylactic ways to protect the entire fuel system.  The most common fault codes for “low fuel rail pressure” are P11C300, P019185, P11B600, P11BB00, P0087, P0087e1, P0088, 171600, 162500, P2226997, P226900 and P226997. See Mercedes Service Bulletins LI07.04-N-060527, LI47.20-P-045500, LI47.20-P-054504 and LI47.20-P-054958. All of these bulletins are about “low fuel rail pressure”. If you have these symptoms or fault codes, check fuses first. Assuming the fuses are ok, I would replace the fuel filter. Open the old fuel filter with a metal oil filter cutting tool. If you find metal in the fuel filter the entire fuel system will have to be replaced as per Service Bulletin LI47.10-P-046862. If you don’t have metal, perform the fuel system test to determine the cause.
B20 biodiesel is another problem to avoid at all cost.  There are fuel stations selling B20 from unmarked pumps.  B20 biodiesel will quickly clog the fuel filter. When a DPF regeneration cycle is interrupted, B20 fuel dilution quickly turns the engine oil into black jello. Once again, this is why it’s so important to know when the DPF is regenerating and what things will interrupt the regeneration.
Metal in your old fuel filter is big trouble. Things are going to get expensive. I like to put a strong magnet on the bottom of the fuel filter. When you change the fuel filter, open the old filter with a special cutting tool for opening metal oil filters. If you see any metal in the old fuel filter, it’s coming from the High Pressure Fuel Pump. You need to start adding a lot more lubricity into your diesel fuel.

–  Catch Tank:  The emission control laws say crankcase combustion vapor cannot vent into the atmosphere.   When the engine’s running the crankcase combustion gases must be self contained.  The engine has to recycle the crankcase vapor.  The BlueTEC has a PCV valve that sends the crankcase vapor into the Turbo where it continually recirculates through the EGR and the air intake system.  Mercedes has updated the PCV valve 14 times.  It will need to be replaced on all 2018 and older models.  The PCV valve should be replaced every 60K as routine maintenance.  The PCV valve slows down the hot crankcase vapor from Blow-by and Direct Injection (DI).  Direct Injection is the current fuel injection design used by most manufacturers to reduce emissions.  But DI also has a downside.  This design creates a lot more crud in the air intake track.  Watch the YouTube video I mentioned earlier.  Eventually oil sludge coats the air intake track.  The only way you can keep this crud from building up in the air intake is with high quality oil, frequent oil changes and a Catch Tank.  Catch Tanks are approved by the EPA.  Mercedes cannot deny your warranty if the Catch Tank is installed properly and appropriate for the engine.  The problem is, no one makes a Catch Tank specifically for a BlueTEC diesel.  However, there is a billet Catch Tank that works perfectly.  It removes all the dirty crankcase oil vapor that normally goes into the Turbocharger.  After the dirty crankcase vapor goes through the Catch Tank only clean air is returned into the Turbocharger.  The Catch Tank keeps hot oil vapor from getting into the DPF.  The cleaner you can keep the DPF the fewer times it needs to regenerate.  I’ll say it again, it’s the extreme heat required for burning off the soot and oil vapor in the DPF that does much of the damage to a BlueTEC.

–  Oil filtration:  Diesel engines produce soot.  Soot is the black nasty smoke that comes out of a diesel exhaust.  The soot coming from a diesel is loaded with nitros oxides (NOx) and other cancer causing chemicals.  The days of half hearted attempts at reducing nitros oxides and deleting the emission system when no one is looking are over.  Soot is the number one enemy of your engine and the air we all breath.  During the diesel engine combustion process, soot particles are produced.  Soot is either exhausted into the DPF or absorbed by the engine’s lubricant.  Soot contaminated oil has been shown to produce significant amounts of engine wear.  The main mechanism of soot-related wear is through abrasion.  Increased levels of soot content in the oil causes the Timing Chain to stretch.  High concentrations of soot can increase the local acidic level and, around the piston where high temperatures and volatile gases coexist, corrosion will also occur.  Today’s best diesel oil will suspend soot particles within the lubricant and keep them from clumping together.  Vehicle service intervals are currently dictated by the length of time that lubricants can maintain their physical properties, but also, and possibly more importantly, by the length of time they can hold soot particles in suspension.  Mercedes uses a cartridge oil filter that removes soot particles down to 30 microns.  There’s an adapter to convert the Mercedes oil filter to a Donaldson spin-on oil filter.  It filters soot particles down to 10 microns.  Less soot in the oil means less Blow-by at the piston rings, less crud in the DPF and longer Timing Chain life.  Change the oil every 5,000 miles and replace the Mercedes oil filter every 2,500 miles and the Timing Chain will never fail.

– Rear wheel speed sensors Recall 2021020026: Model years 2012 to 2018. This is most noticeable on RV’s, but effects all Sprinters. The ABS or ESP warning lights come on. The RV can drive very unstable. Some owners have replaced the rear wheel speed sensors several times. Mercedes will pay for new rear wheel speed sensors and reimburse you for previous rear wheel speed sensor repairs.

–  And then we have the dumb stuff:  Things that should never happen.  Starting in 2019 the OM642 diesel doesn’t come with an engine oil dipstick.  Mercedes puts a cheap oil plug in the dipstick tube that often blows out and sprays oil all over the engine.  

New Sprinters also have a problem with one of the Power Steering hoses popping off a fitting at the radiator.  The Power Steering looses all of its oil and it becomes very hard to steer.  Mercedes has been screwing around with this problem for 20 years.  Mercedes says you should install a different hose clamp.  The problem is not the clamp.  The problem is the hose is about 13mm too short.  Over time the movement of the engine pulls the hose off.  There’s an easy way to lengthen the hose with a magnetic Power Steering filter and a better clamp.  See Service Bulletin LI46.00-N-068838.

If you own a OM651 4 cylinder BlueTEC, you’ve got some all time stupid problems.  The OM651 has the goofiest water pump in the world.  Its design allows coolant to enter the engine’s vacuum system and eventually enter the electrical, brake booster and vacuum pump.  If you ignore the “low coolant” light it can ultimately ruin the engine.  This repair is outrageously expensive.  There’s a simple way to monitor the problem and catch it before it causes so much damage.  See Service Bulletin LI07.09-N-063338.

The OM651 also uses a single roller timing chain that’s at the rear of the engine.  The engine and transmission must be removed to replace the timing chain.  Once again, the repair cost is outrageous.  Protect the Timing Chain with frequent oil changes.  See Service Bulletin LI05.10-N-057796.

The OM651 is a good engine but it has some peculiar problems that are unique to the OM651.  I’ve put together 3 manuals that cover all the problems and how to prevent them.

For years, Sprinter owners have complained about howling noises from the front or rear differentials.  Year after year Mercedes publishes Service Bulletins that say they are investigating the problem.  (See Service Bulletin LI33.30-N-071003.) The noise is actually caused by “fuel efficient” differential oil. Over time, the oil fails to protect the bearings in the differential.  Change the differential oil with Castrol ‘SAF XJ’ 75W/140  MB p/n: 001.989.52.03.10, ASAP.  You’ll also need a magnetic drain plug, p/n: 000.990.58.17.  See Service Bulletin S-B-00.20/102a.

Sprinter owners complain about intermittent clunking noises from the driveline on load changes.  The noise is caused by excessive free play in the splined connections of the drive shaft and axle shafts.  They need to be removed and coated with a thick glue called OmniFIT 100H.  Mercedes published Service Bulletins about this same complaint 40 years ago.  They used the same OmniFIT to stop the noise.  See Service Bulletin LI35.30-N-049982.

Some late model 907 and 906 Sprinter’s with the OM642 report an intermittent problem of no power when the engine is near freezing. Often at high altitude.  After the engine warms up for a minute it runs normal.  It may do this very intermittently when driving in cold weather at high altitudes.  Most of these are still within warranty. I won’t say nobody knows what’s causing this, but it’s rumored Mercedes has bought back a couple of Sprinters because of this. See Service Bulletin LI14.20-N-071638: The EGR cooling solenoid valve (Y27/13) intermittently sticks causing a lack of power. You may or may not find Fault Code P2459. I think condensation is getting in the valve and it freezes. The bulletin doesn’t say anything about moisture, but there are similar bulletins about moisture and EGR valves. When the engine warms up the moisture thaws and the solenoid starts working again. A shop test always shows the solenoid is normal because it’s not cold enough. Plus there needs to be enough moisture in the air to make it freeze.
Another possibility is the EBP (Exhaust Back Pressure Sensor / in the EGR cooler), the DPS (Differential Pressure Sensor) and the IPS (Intake Pressure Sensor p/n: 005.153.50.28 – green label) may need to be replaced or have a “Teach-in” performed.
Don’t forget, the wrong oil viscosity in cold weather can also cause the engine to feel sluggish after a cold start. Use the appropriate 0W/40 or 0W/30 oil viscosity in extreme cold. If you drive in constant subzero temperatures, there are other oils for that. An Ester based synthetic 0W/30 would be the best choice. Ester synthetic flows better in extreme cold. There are Block heaters, fuel, battery, oil and AdBlue tank heaters for subzero weather. You should also give the engine a couple of minutes to warm-up in subzero weather. Start the engine and raise the idle to about 1,000 RPM’s. Then start driving.

Service Bulletin LI03.10-N-071148 – dated 6/4/2020 (OM642 and OM651): The bulletin explains a rough idle caused by bent connecting rod. Condensation from the PCV crankcase ventilation system enters the Intercooler (Charge air system). Water causes one cylinder to hydro lock. Compression is slightly lower on cylinder #6 in the OM642 and cylinder #2 in the OM651. The engine is ruined. This applies to all Sprinter chassis 907 and 906 with the OM642 and 906 with the OM651 up to production date 2/2019. After that date the Intercooler and hose were updated at the factory. A few weeks ago I had a new owner contact me with this problem. He had less than 1,000 miles on a new Sprinter RV. Condensation in the Intercooler caused one cylinder to hydro lock and his engine through a rod right through the engine block. This is not common, but it has happened. Here’s the tough part of this problem. What if the connecting rod is slightly bent? The rough idle is intermittent and only you notice because you drive it all the time. Maybe the idle is slightly rough when the engine is cold. It is not a Recall, but it sounds like Mercedes might preemptively replace the Intercooler and hose as Goodwill. It wouldn’t hurt to ask. Mercedes doesn’t say what causes the condensation. They only say it happens “under certain conditions”. I suspect it happens in areas with cold weather and high humidity. Short trips or excessive idling will always cause more trouble. The updated part numbers are in the bulletin. A Catch Tank always prevents any condensation or oil vapor from getting into the Intercooler. That’s its job. Plus a Catch Tank cost less than an Intercooler.

Service Bulletin LI20.30-P-069996 – dated 7/2/2019 (OM642 and OM651): Oil in the cooling system. The Heat Exchanger is warped and oil is leaking into the cooling system. Oil is in the coolant recovery tank. The Heat Exchanger is attached to the Oil Filter housing. Replace the complete Heat Exchanger and not just the gasket. Replace the Coolant Recovery tank. Follow work instructions in the service bulletin. Don’t forget, Mercedes changed the type of antifreeze in April 2014. Prior to that date the antifreeze is Blue, p/n: Q103.00.04. After that date the antifreeze is Pink, p/n: Q103.00.05. Flush oil from the cooling system with Cooling System Cleaner, p/n: 002.986.42.71. You may need to flush the oil several times. Oil in the cooling system will attack any rubber hose or seal. If oil has been in the system very long, over 3 months, you’ll have problems with leaks. Don’t forget, the radiator has rubber seal between the plastic tanks and the metal cooling fins. If this happens on the OM651 four cylinder diesel, you’ll have a much bigger problem than can be explained here.

The High Pressure Fuel Pump can work loose and cause a knocking noise at idle.  Mercedes says mechanics should ignore the noise.  (See Service Bulletin LI07.16-N-070308)  But Mercedes training documents tell a different story.  The Training Center says the High Pressure Fuel Pump can work loose and break one of the three bolts holding the pump to the engine block.  The High Pressure Fuel Pump works loose and jams the Timing Chain.  (OM642 and OM651)  That breaks the Camshaft Gears.  This is an easy $8,000 repair that’s easy to prevent.  The mounting bolts have been hardened and are made with thread locker; p/n: 001.990.93.03.  The 3 bolts cost less than $5 and take less than 5 minutes to replace.  It’s your call.  See Service Bulletin LI07.16-N-070308 dated 9/2019.  (If the bolts are tight, and you still have the knocking noise, the fuel does not have enough lubricity.  You should not ignore a knocking noise from the High Pressure Fuel Pump.

Over the last few weeks I’ve had a heart to heart talk with owners about what they honestly think about the article and what type of help they would like to have. Most like the technical details, but it scares the hell out of them. Several people have new BlueTEC Sprinters on order. After reading the article they wanted to cancel their order. NO, please don’t cancel your order. Several of them have friends or a relative who were BlueTEC mechanics. Some work at dealers. They all advised against buying a new BlueTEC. NO, please don’t cancel your order. But, I need to simplify this article. New BlueTECs are great vehicles if you understand a few basic preventive maintenance items. Seriously, do not cancel your orders. Once you understand how the BlueTEC works, it’s not so scary. When you start off with the proper maintenance, they will be great. Dealer mechanics can’t tell you about all the preventive maintenance. Their hands are tied. I hope this article hasn’t given people the wrong impression. All of the new and used BlueTEC problems can be solved. The longer you wait the more it cost, but Sprinters really hold their value. Over the next few weeks I’ll start simplifying the article. I was afraid of this. It’s all true, but maybe it’s better if I verbally explain it and sugarcoat it a little.
I’ve asked owners for feedback about the cost of personal help. Some owners have a substantial mechanical background. They’re easy. I send pdf files about the problems in every system. Mercedes publishes their information in a disjointed method. I rewrite everything so it explains all the problems so it makes sense to owners. Then I spend a few hours explaining and answering questions. Some people have complicated problems or they don’t have mechanical experience. Some people don’t have access to a good BlueTEC mechanic or their fighting with their dealer. I have 6 owners with Sprinters in the shop for over 3 months. These take more time. I understand and I’m ok with more explaining. But I have to charge $500 for more comprehensive help. We’ll talk about it before you decide to commit. I’ve retired and the money goes to my Grandson’s 529 College Savings account.

Every vehicle and owner is different. If you send me a email, I’ll explain what you can expect. The pdf attachments are large. Gmail works the best. Other email servers will often reject the attachments.
If you want more information you can email me at: tom54stephens@gmail.com. (Tom Stephens 916.715.0665)