Here is the blog post in question:

http://www.stephensservice.com/bluet...ssuesproblems/

My dream car is a 2012-2013 Mercedes S350 diesel, but I am not an expert about these issues, so I'm really conflicted here. I am quite willing to buy used parts, even buy a used engine eventually to keep it in working order, but I read a blog post by an ex-Mercedes mechanic that absolutely said this engine (in particular the mercedes version in the S350) is a disaster zone in terms of design and complying with restrictive US EPA regulations and unwise engine oil requirements promoting fuel efficiency over longevity. He says 5W30 oil is absolutely the wrong oil in most climates, unless it's literally subzero all the time (I live in Houston).

He also said the 10,000 mile oil change interval is entirely inadequate for these diesel engines due to excessive heat associated with the turbo which gets fed directly into the engine oil (8.5 quarts capacity is actually worse because it heats up faster). He claims the diesel fuel mixes with the relatively thin oil and this allows the hot oil to cause major problems for the engine over time that just get progressively worse with age (due in part to vaporization). The only oil he recommends for OM642 engines is high weight motorcycle oil, like Amsoil. He says nothing else can withstand the intense heat, and even then, the proper oil interval is 5000 miles maximum. This oil tends to also be very expensive, but if it's protecting my engine it's arguably worth it. He also said, do not disable the bluetec system.

One possibility I'm considering is only buying a car that has been in California's mild climate it's entire life and been driven mainly as a highway cruiser, because the short stop and go abuse that most cars are subjected to is entirely unsuitable for this engine and the recommended oil and change interval. I know there are people who have owned these cars and haven't had any sort of major problems. I know a guy in New York that operates one of these vehicles as a luxury limo outside of New York and has 300,000 miles on his engine, so there's got to be a way to efficiently care for this car in a way that is economical if he's operating a business with one. Please convince me this isn't the worst decision I've ever make in terms of a used car.

Thank you.

 

I think this might just be a very small sample of a few that have had these issues. My neighbor has a 2011 GL350 since new and had 100k on it with no issues, and she drove it sometimes 3-4 times a day only going on small trips. Most of her travel wasn't long.

 

Thanks for that insight. I have no doubt these cars don't completely break down before 100K miles, but getting to 200K may be an issue for some in my view.

 

I appreciate your concern for reliability but you do realize in your signature you have the SC430 which is considered to be the worst car ever produced. It might be reliable but there is nothing else it is good at so maybe the S isnt the right car for you since you value reliability above everything else

 

I didn't realize this car was so poor when I bought it. I bought it on impulse because I liked the way it looked and seemed classy and unique.

 

I've read this before with different model engines. You can write the same review day after day and simply replace the line that says engine.
In my experience when it comes to pretty much any engine when it comes to oil changes change the oil as needed in relation to how you drive Gas or diesel. I change the oil on my BMW's and Mercedes gas engines every 7500 miles or one year from last service whichever comes first, Well below the recommended miles. When comes to diesel there are differing opinions. A fleet manager from Penske that I recently purchased an International from said they go by the hours not the mileage. My regular diesel mechanic says to change the oil and all the filters every 5000 to 7500 miles. I run dual oil and fuel filters as well as a 32 quart sump to extend the oil life to roghly 10,000 miles or every 6 months usually. It deopends how busy I am. I'm running two FL80's with CAT 3126 motors that are pre-emmisons and none wet sleeve motors that are tuned down to 210 HP each. that have over 600,000 miles on each one. These motors were designed to NOT go past 500,000 miles. It;s all about mainetence and quality of fuel.

With an emission diesel, you need to be even more strict when it comes to changing the oil and filters. On a blue-tech I would change it every 6000 to 7000 miles. In my experience it's those last couple of thousand miles that leads to the engine being coated and soot and the turbo pipes and one box filter getting choked up. Once that happens the regen process is useless.

 

Well I suppose the issue is it's almost impossible to find an OM642 that has verified oil change intervals less than 7000. I know because I've looked at the relatively small market of S350's in the US for weeks now. Often these cars are lease vehicles, therefore there's no incentive to care about engine longevity, and merdeces themselves seem to be encouraging the long term damage of these vehicles at 10,000 standard maintenance intervals, which is almost always seen in less than a year of driving. BMW was even worse for a while at 15,000 mile oil intervals, only recently switching to 10,000. It doesn't help the fact this may be a backdoor way to encourage planned obsolescence, because there's no way 10,000 mile oil change intervals are ideal for all driving conditions. I would challenge someone over 100,000 miles to prove otherwise on a 5-6 year old vehicle with an formal oil analysis.

 

I hesitate to post in this thread, given the tone of some of the posts, but it seems to be the most relevant thread.

I've just stumbled across the Stephens Service Centre web pages. They alarmed me. However ... I have a 2015 GLC 250d with the OM651 engine rather than the OM642. And I'm not in the US, so comments about how diesels were configured for the US don't apply to my vehicle.

So my question is ... how much of the Stephens material applies to my engine?

 

Australia is a fairly mild climate, so that helps a lot from what I understand. It's these very cold climates that seem to be doing a significant amount of damage to these engines before the oil reaches ideal temperature. But hot climates also hurt the engine, because the turbo engine runs so hot anyway. And since diesel fuel is mixing with the oil, it creates issues. If it's running the bluetec system to keep the emissions clean, then you will have a lot of the same issues. Regardless, these engines are oil burners, so you either change the oil super frequently to avoid the issues he spoke of, or you're going to do long term damage to your engine. We're talking about miles here, so I would not exceed 3000-5000 miles depending on your driving. If you do mostly long highway trips, then opt for 5k. If you're doing a mix of city and highway, do 3000. That's just my best interpretation of what the underlying issues are here. But if you bought the car used, there's likely already minor damage done to it, so do the oil flush he spoke of.

 

One thing I've learned over the years is to never take an advice from a mechanic. Why? Mostly because their perception and experience is of a person that deals with a problem after problem. They never get to see the "good" stories that no one ever talks about. And as you can tell by the forums alone, there is no good stories. Mostly people looking for resolutions to problems.

When it comes to reliability and buying used cars, here is my criteria.
1. Service records - has the car been well maintained. Before you even consider "general" reliability, this one is WAY more important in my eyes. Life of <insert any machine> depends on the maintenance of the item. I would rather take well maintained S class over neglected Honda or Toyota.
2. Condition of the car/previous owner - interior is usually a good indicator of the kind of a person that owned the car. Take a good overview look of the car and see if the owner cared.
3. More complex the car > higher the risk for failure

In general, here is my recommendations when it comes to S Class

Pro
- S Class owners usually tend to take their car to all of the scheduled maintenance, and it's recorded!
- Amazing car and most importantly feeling it give you/experience. Hard to put value on this. But whatever your happiness levels are in a given moment, driving this car will improve it hehe
- Quality of materials. Leather, Paint and many other items are simply hard to surpass.

Cons
- it is an extremely complicated/complex car, which means lower reliability (more things that can break). I simply accept that I can wake up tomorrow and the car might be totaled (this makes me enjoy and appreciate the car more). I also recommend having 3-5k ready to go at any given moment.
- If you are not handy/work on these cars, it will cost $$$ to maintain or bring it anywhere
- people think you have money and will charge you a premium

 

As a mechanic I can agree with this. Also the old timers with that much experience tend to hate every newer car. Every model has its share of problems, buying a used car you will most likely have to deal with problems. Just get a pre purchase inspection done on the vehicle by an experienced shop. I've seen a locked up bluetecs at 40k miles and have seen some sprinters with 300k+miles.

 

Hi guys please could you assist me regarding my s350 reason being when I drive it gives a small fish bite kind of felling

 

What does this even mean?

 

maybe the poster was meaning fish smell?

 

Does anyone know the recommended transmission service interval for a W221 s350 including the 4matic differential ? My owners manual says not required for the 642 engine ( V6 Diesel) @ 40K. I have changed the oil all Filters and changed the DEF. The Fuel Filter and Brakes were flushed @33K miles. I now have 39K and trying to get everything finished up.

 

My SA is a diesel fan and says that they wouldn't own a bluetec due to their complexity.

 

According to Maintenance book S-Class W221 with diesel engine OM642 has service interval for transmission every 70k miles. W221 with gas engine has service interval for transmission every 40k miles.
Source:
https://www.mbusa.com/vcm/MB/Digital...ce-Booklet.pdf