People keep 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 tells 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 also requires the combustion temperatures keep increasing to burn the fuel more completely and reduce the hydrocarbons.  Low viscosity oils can’t handle the high heat.  A BlueTec diesel needs higher viscosity oil to resist thermal breakdown from the heat.  The engine 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 bearing from extreme heat.  The engine also needs the additives to protect the timing chain from wear.  Zinc protects the timing chain from stretching.   EPA oil allows for about 900ppm of zinc.  The timing chain needs about 1,400ppm to 2,000ppm to keep from stretching.  Mercedes has admitted that the timing chains are all failing.  Fuel Dilution also causes soot to get in the oil.  Soot is abrasive and 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 is 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.  Ice crystals will also form in the Oil Separator and damage the Turbo Impeller.  Condensation in the rest of the oil freezes and damages the pistons rings.  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 is also a very good idea.

If you drive where it’s real hot, you’ll need a oil for high temperatures.  Like a 20W/50  or a 10W/60 oil.
If you make short trips where the DPF doesn’t have time to regenerate, the oil is contaminated with a lot more diesel fuel.  The oil needs to be changed very frequently.  If you drive on the freeway, the oil doesn’t get as much diesel fuel in it, & you can go farther on oil changes.

If you use B20 biodiesel, the problems get way worse.
There are other additives that I like to use in the oil.  I know Mercedes says no additives.  In my opinion, if Mercedes wants owners to take their advice seriously, they need to take responsibility for all of their known problems.  They leave owners twisting in the wind with vague and contradicting statements about the correct oil.  Mercedes knows exactly what they are doing.  They know fuel dilution is a major problem.  Mercedes knows the current oils cannot deal with 1600F.  There are no oils that can deal with those temperatures.  If 1600F is not a problem why does Mercedes build a water cooled Turbo and water cooled Intercooler for the Military and First Responders?   The new inline 6 cylinder Diesel engines in Europe, are all water cooled.  The new V8 diesels they send to Russia and China are all water cooled.  Why did America and Canada get stuck with the cheapest Turbo Garrett makes?  Why isn’t Garrett allowed to even sell a water cooled Turbo for the American OM642 Diesel engines?  Garrett makes the water cooled turbocharger for the OM642.  But Mercedes and the EPA blocks them from selling it in America.

So, what oil is best for your OM642 or OM651 BlueTec diesel?  As you can see, it all depends.  The EPA diesel oils are generally not good enough.  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 not 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.  Hopefully you’re beginning to see that 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.

BlueTec diesel owners need to understand that they are on their own when it comes to dealing with this engine.  Mercedes & the EPA know they don’t have oils that can withstand the temperatures the emission systems are required to operate.  This is one of the reasons I recommend Motorcycle oils in the past.  Those oils have no EPA rules & are made to withstand extreme temperatures in high performance motorcycles.  I still like Motorcycle oil, but it does need a additive to help with the soot in a diesel.  BG “DOC” is a good additive for helping Motorcycle oil handle the soot and acid levels in a diesel.  I think 5000 mile oil changes will keep the soot from damaging the engine.  You can also change the oil filter every 2500 miles.  There is also a company that makes a billet oil filter housing that will take the extra big oil filters that come on heavy off road equipment.  Those bigger oil filters are designed to filter out the soot in diesel oil.  Soot is abrasive and is one of the reasons for timing chain failures.  I shouldn’t have to tell people about this.  This is Mercedes responsibility.  They should clearly tell owners what’s going on and what oil they should use in all the different driving conditions.

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.

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 will tell you how to stop the oil burning without taking the engine apart.  If your engine has already locked up I will 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 hear 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 “”.  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.  (916.715.0665)