I can’t believe how many people incessantly argue about the correct oil for a Diesel engine.  My name comes up more times than I care to imagine.  Then people start calling me wanting to know what’s the best oil for their BlueTec diesel. They don’t want a long explanation, “just tell me the best oil?”  No problem.  Use Redline 15W/40 diesel oil.

For those of you that want to understand this problem, keep reading.  The Redline 15w/40 is a decent oil.  It’s way better than the Mobil One 5w/30 ESP dealers are using.  But it’s not the ideal oil for most owners.

The EPA uses the API / SAE to tell all manufactures what the oil specs must be for all types of engines.  The EPA wants to reduce pollution by reducing the viscosity for better fuel economy. Better fuel milage means you burn less fuel.  The EPA regulations also force manufactures to constantly increase the combustion temperatures.  Higher temperatures reduce unburnt hydrocarbons.  Low viscosity oils breakdown as the combustion temperatures increase.  A BlueTec diesel needs higher viscosity oil to resist thermal breakdown from the heat.  It also needs the high viscosity to withstand the high fuel dilution caused by regenerating the DPF.  The EPA has also reduced the additives in oil.  They say those additives “poison” the catalytic converters and the DPF.  A BlueTec needs those additives to protect the Turbo bearings from extreme heat.  The engine also needs the additives to protect the timing chain from wear.  Zinc is a oil additive that protects the timing chain from stretching.  The EPA has reduced zinc to about 900ppm.  Timing chains need about 1,400ppm to 2,000ppm of zinc to keep the chain from stretching.  Mercedes admits the timing chains are all failing.  Fuel Dilution also causes extra soot to enter the oil.  Soot is abrasive and also causes timing chains to wear.  The oil in a BlueTec diesel has to work much harder than the oil in a gas engine.

The EPA has a long list of specifications the oil has the meet.  I personally think the NOACK Volatility test is the most important.  In order for a oil to achieve a low NOACK Value the rest of the oil specifications have to be very good.  A low NOACK value is the hardest to achieve.  When oil gets hot, a certain percentage turns into steam.  The EPA regulates the amount of steam or oil vapor the oil is allowed to have.  The EPA knows this oil vapor will eventually get to the catalytic converter and the DPF.  The EPA only allows diesel oil to have a maximum NOACK value of 13.5%. A NOACK value of 13.5% is not a good oil.  The Mobil One ESP that Mercedes dealers recommends has a NOACK value of 24% after 3 hours running.  That’s twice as much as the maximum the EPA allows.  Exxon Mobil admits to this in an internal document.  They even admit they intentionally hide the NOACK value from the public.   If the oil doesn’t list its NOACK value on its Material Data Sheet, it means it has the maximum the EPA allows.   Any oil with a low NOACK value is proud of that and they list it on their Material Data Sheet.

Really great diesel oil has a NOACK value of less than 5%.  That means the oil doesn’t vaporize & turn into sludge.  When oil gets hot, the steam that comes off is made up of the lighter chemicals in the oil.  Those boil away first and a thick sludge is left behind.  But the fuel dilution from regenerating the DPF washes past the Piston Rings and into the oil.  Now the thick sludge in the engine is thinned out by the diesel fuel.  Obviously this really upsets the chemical balance of the oil.  The better the oil is to begin with, the better it can handle the heat and fuel dilution.  Now multiply all of this by 20,000 mile oil changes.  Take a guess what the oil in your crankcase looks like?

Then you have the ambient temperature to consider.  If you live where it’s below freezing, it takes oil with a viscosity that’s designed for cold temperatures.  As you drive during the Summer, the engine oil picks up the condensation that naturally occurs.  When Winter arrives and the moisture freezes, it thickens the oil.  Ice crystals also form in the Oil Separator.  When you start the engine on a cold morning, the ice crystals hit the Turbo Impeller and act just like sand.  This is why Turbo’s have more trouble in cold climates.  The frozen condensation in the rest of the oil damages the pistons rings on cold starts.  That causes Blow-by which puts even more pressure on the Oil Separator.  It is extremely important to change the oil every 3,000 miles in freezing weather.  A Block Heater also keeps the condensation from freezing.

If you drive where it’s real hot, you’ll need high viscosity oil for high temperatures.  Like a 20W/50 or a 10W/60 oil.  These are listed and recommended in the current Owners Manual.  The problem is, there is no MB229.52 oil with these viscosities.  Speaking of the Mercedes oil rating system. The Owners Manual list several MB229.xx oils that are approved for the BlueTec diesel.  However, Mercedes has several Service Bulletins that say only the MB229.52 oil is approved for the BlueTec diesel.  Mercedes also doesn’t publish any Material Data Sheets for any of their oils.  What’s the big secret?  Why won’t Mercedes let owners compare the actual chemical breakdown of their oil with other oils?

So, what oil is best for your OM642 or OM651 BlueTec diesel?  As you can see, it all depends. What type of driving you do.  Do you drive in freezing weather?  Do you tow?  Do you drive in the mountains in hot weather?  Does your engine have a Catch Tank?  Does your engine have the 8.5 quart oil pan or the 13 quart oil pan?  Does the engine burn oil?  I’ve read hundreds of Material Data Sheets looking for the lowest NOACK values with the highest VI, (Viscosity Index).  The oil needs a VI above 160 to maintain it’s viscosity when it gets hot.  If you’ve got a Oil Separator that’s never been updated, you can have the best oil in the world, and the Turbocharger will suck it right out of the engine and into the EGR.  If the air filters are dirty it will cause even more oil to be sucked out of the crankcase.  The Air Filters must be pristine.  Oil is only one piece of the puzzle.

Let me explain how the EPA NOACK Volatility heat test works.  The EPA heat test only goes up to about 450F.  Your BlueTec Turbo sees temperatures of 1600F.  Some people don’t believe it is possible for the Turbo to get to 1600F.  I can send you the data directly from Mercedes and Garrett.  They both admit the Turbo runs at 1600F.  The EPA test don’t even get close to 1600F. The EPA knows that a BlueTec will hit temperatures way above their test ranges.  Mercedes-Benz and Exxon Mobil also know their recommended oil can’t come close to withstanding these temperatures.  They’ve known it for over ten years and they refuse to fix it.  They know their recommended service intervals will destroy the engines.  They advertise that you can go 20,000 miles between oil changes and then they publish service bulletins that tell dealers to “greatly reduce the service intervals”.  Mercedes knows their dealers will never pass that information on to the customer.

This is a direct quote from the FAQ section on the Garrett Turbo website.
Q.  Should my turbo/exhaust manifold glow red after driving?
A.  Yes, the turbo/exhaust manifold can glow red under certain driving conditions.  The exhaust gas temperature can reach over 1600F under high load operating conditions; i.e. towing, extended uphill driving, or extended high rpm/boost conditions.
Your engine oil goes through the Turbo.  Oil & air are the only things that cool this Turbo. If the DPF is regenerating while your driving up hill, the Turbo can even get hotter than 1600F.  Garrett makes the Turbo that Mercedes-Benz uses on your OM642 BlueTec.  This extreme heat is why the Turbo Impeller shaft bearing fails.  The oil gets so hot it turns into tar and the bearing fails.  There is now a company that makes a special Turbo oiler that pushes a quart of oil through the Turbo after you shut off the engine.  It prevents what’s called “Heat Soak”.

I get so many calls about oil that I don’t have time to help owners with their specific problems.   I’ve kept doing this in order to fund my Grandson’s college savings plan.  For $200 to his college fund, I will send you all the technical data and maintenance information you can think of.  I will look at your maintenance history and tell you what’s the best oil for your specific situation.  I’ll also explain how you can prevent expensive repair bills and get your engine back to good health. If you have a new Sprinter I will explain everything about breaking it in and how to keep the sludge out of your engine forever.
If your engine is burning a quart of oil every 200 miles, I’ll explain how to stop the oil burning without taking the engine apart.  If your engine has already locked up I can show you where and how to get a rebuilt engine for half the price Mercedes wants.

However, I just can’t answer dozens of emails and phone calls each day asking for free advice.  I know these diesel problems are quite stressful.  I’ve  heard all the stories.  I wish I had the time to answer everyones questions.  But it’s not fair to the owners who are helping my Grandson save for college.  If you don’t think it’s worth $200, you can always get answers from the Mercedes technical website “startekinfo.com”.  It is $60 for 24 hours.  You can also call 1-800-FOR-MERC and ask for customer assistance.  They will answer questions at no charge.

Another point has been brought to my attention.  Owners tell me my articles have caused quite a few discussions on various Owner’s Forums.  People have ask me to respond to criticism from a few regulars on these websites.  There are a few people on these Owner’s Forums who tend to dominate the conversations.  When someone is critical of Mercedes these people respond with some comment that belittles the original question.  They typically say they have never had any trouble with their BlueTec diesel.  They also think I’m long winded and full of crap.  Then I notice that these people have posted 5K, 10K and even 20K times.  Are you kidding!  That’s a full time job telling everyone you’ve never had any problems with your BlueTec.  Excuse me, that ain’t normal.
tom54stephens@gmail.com  (916.715.0665)