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When any internal combustion engine - not just our particular MB units - is started from a cold condition, some of the fuel that is delivered to the combustion chamber and is yet to be ignited or remains unignited during the combustion process is going to be forced into the crankcase between the piston rings and the cylinder wall. (This is not the only time fuel dilution happens but it is a significant time.) There are multiple reasons why.

One reason is that during a cold start the various metals that comprise the engine parts are not yet heated to the temperatures at which they are to designed to most effectively/efficiently operate. Different types/shapes/sizes of metal parts have differing expansion and contraction rates. Until all of the various metal parts in an engine have reached their optimal operating temperature and therefore their optimal expansive state, the gaps/tolerances/clearances/whatever will not have reached their design parameters and there will be (for lack of a better term) a misfit, however minuscule, between the piston rings and cylinder wall. This misfit will allow for the compression forces in the cylinder to more easily than normal push unignited fuel between the rings and wall into the crankcase. While the high compression ratio, turbocharged engines such as ours provide for better overall performance they may actually be a negative factor in a cold start situation as the increased compression forces could serve to push a greater amount of unignited fuel into the crankcase until the engine is warmed up. Further complicating the equation is that a direct injection engine such as ours uses a very high-pressure injection system to deliver fuel directly into the cylinder (as opposed to a port/throttle bore injection systems and carburetors). Add into the mix that the fuel to air ratio is increased (more fuel, less air) during cold start-up in order to enable immediate driveability and you have a recipe for fuel dilution to the oil, in my mind. The more cold starts you do, the more fuel gets dumped into the crankcase. It seems inevitable.

So, you may ask, why doesn't every turbocharged, direct injected engine suffer from consistent, pervasive and massive fuel dilution to the oil. Operational factors and conditions account for some, or maybe even a significant portion, of the reason. Design and implementation are also important. (I can't help but wonder if the Eco mode operation and engine cut off mode during stops may even be a contributor.) If you cold-start your car, get out on the highway (not stop and go operation or extensive idling, which are also contributors to dilution) and drive for some distance, the fuel that makes it into the oil at start-up will eventually evaporate as a result of the oil becoming heated to a point that will promote evaporation. If an engine sees nothing but long-duration operation after every cold start there is a high likelihood that dilution will never be a major issue absent some mechanical malfunction. Several factors come into play with evaporation from usage as a fuel dilution control method; how long does it take to get the engine oil to a temperature that evaporation will occur (more variables at play here) and how long will it take to evaporate all the fuel that is there given the oil temperature at which the engine is designed to operate (even more variables at play here). Since we do not know and MB will likely never voluntarily disclose the answers to those questions, it is really a guessing game for us in determining if our engine suffers from dilution. But the guessing game can be a bit less guess and a bit more scientific with testing. Unfortunately, no one (including my obsessive self) is going to realistically be able to make all the tests that would be necessary to ascertain all the pertinent answers.

However, I have concluded (through oil analysis) that at some even moderate level of dilution, with respect to the engine in my car, evaporation through even extended operation is not sufficient to purge all previously accumulated fuel from the oil. Perhaps if MB were to design the engine to operate with the oil at a higher temperature level, it would be more conducive to quicker and more effective evaporation of fuel. My seat-of-the-pants thermometer (tactile contact during my multiple testings and changes) suggests to me MB doesn't allow the engine to operate with a very high oil temperature at all. So why not? One of many factors could be that the hotter the oil runs, the quicker it deteriorates and the sooner it will need to be changed. This would not be conducive to MB recommending a 10,000 mile/one year oil change interval. They may have to shorten the change interval or revert to the "olden days" of engine technology where a manufacturer would make one oil change interval recommendation for normal usage and a shorter interval recommendation for severe service usage. And if you are too young to remember, short trip usage was one of the severe service categories. Why? Fuel dilution because of incomplete evaporation from use is one reason.

Then why doesn't MB have differing intervals of oil change recommendations based on use patterns? Maybe they want to appear to be on the cutting edge of technology and not be seen as living in the olden days. (If so, they should implement an algorithm like other major manufacturers which would more accurately estimate when the oil needed changed instead of using a single time/mileage recommendation. But then that probably would not result in many 10,000 mile change intervals.) Maybe they want to appear environmentally friendly by establishing extended change intervals, or governments may even be forcing promotion of environmental conservation. Maybe they want to sell more replacement parts/engines to subsequent owners of a second-hand MB who are clueless that despite records to indicate all service was done at the manufacturer's specified interval the engine is prematurely worn out because of an improper oil change specification. Maybe they want an entry-level MB purchaser to be so impressed with the ease and economy of MB ownership they will buy another one - sooner rather than later. (Think how unimpressed with MB someone would be to learn they needed to service an engine every 2,000, 4,000 or 6,000 miles, especially if they have to pay for it at a dealership. ) This last "maybe" happens to coincide with one of MB's stated reasons for introduction of the GLA to the US - lure first-time, younger buyers into the MB culture and lifestyle then upgrade them to a more expensive MB on their next purchase. One could argue that MB has essentially dumbed-down the oil change interval decision for marketing purposes, all to the detriment of good-faith owners who want to do the right thing as it relates to maintenance of their cars.

I realize MB is in business to make money. I do not hold that against them. But I am preparing myself for a big run-around on this issue. And I will hold that against them. I refuse at this point to accept MB's (or anyone else for that matter) suggestion that consistent, pervasive and massive fuel dilution is an innocuous condition. Just be up front and honest about it MB.

My overall point is that it is up to every owner to make good, informed decisions for themselves. If you wish to own a car that has a turbocharged, direct injected MB engine for the long term, following MB's oil change recommendations MAY not be a good decision. The only way to know what is the best oil change interval for your engine is to inform yourself --- do periodic testing under your typical operating parameters until you have isolated an interval that presents no problems (or benefit from the testing of someone else whose operational parameters are similar). One size does not fit all. Sure, it is a PITA and will potentially increase your maintenance costs. (And it may force you to become a gear-head. There are worse things to be.) At least for me, I consider it worth it. If you decide to undertake testing, again let me suggest a lab that uses gas chromatography for their test method as your preferred choice.

Now, if you do not plan to keep your car past the warranty period, do not let all this cause you undue concern (unless it is based on principle). Your car will likely make it through any available warranty period with no problems resulting from fuel dilution, and of course any resulting malfunction during the warranty period will be repaired by MB except for oil use of up to 0.9 quarts per 600 miles (15 quarts per 10,000 mile oil change interval or 2-1/2 times the capacity of the engine sump), which sounds like overly excessive oil use to me. (Seems as though MB covered themselves here in the event of early ring/cylinder wear due to inadequate lubrication resulting from severely diluted oil). As ours is the 3rd generation of this engine design, I imagine MB can tell you (if they would) with an astonishing degree of accuracy what percentage of units they will have to repair/replace and at what point in time/usage given the operating conditions it will take place. But we, the owners, will only know the beginning of problems associated with fuel diluted oil when we hear of worn timing chain guides being replaced, worn cam phasers being replaced, stretched timing chains being replaced and complaints of excessive oil use. We should really pay close attention.
 

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Which engine is this happening with the M270 of the GLA250 or the M133 of the GLA45?
 

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Discussion Starter · #3 ·
Which engine is this happening with the M270 of the GLA250 or the M133 of the GLA45?
My engine is the M270 but I will suggest that ANY gasoline, direct-injection engine is susceptible to the phenomenon. This suggestion is based not only my personal experiences with this and another brand car but on anecdotal evidence (which I have no reason to disbelieve) on other forums. It is that anecdotal evidence that initially led me to discover the problem with my cars. As I contend in my missive, operating parameters play a very important role in the equation. Not everybody's are the same. The ONLY way to know if your particular unit exhibits the condition is to test within your typical usage patterns. (Again, let me emphasize in this new thread that I have absolutely no vested interest in any oil testing laboratory or related business.)
 
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