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I follow what is stated in my specific Mercedes Operators manual. My 2010 C300 4matic Sport says use premium unleaded 91 min. Around my area there is mostly 87,89 and 93, so I get 93.
My vehicle does not say E85 anywhere on the fuel filler flap so I dont use E85. Even though the manual says they are designed to operate on premium unleaded gasoline or ethanol fuel (E85), or any mixture of these two, it goes on to mention for best performance and drivability it is recommended to use either one or the other fuel. Who doesn't want there Mercedes performing and driving its best?
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Originally Posted by LogicalApex
My 2014 C300 can handle E85 fuel and is a Flex Fuel vehicle. Not all C300s are Flex Fuel, but some are. You can tell by looking at the fuel filler cap. It mentions it. You'll also see it on the VIN Decoder site as well.
That being said, you are not correct on the mixing. The car is designed to run on pure E85, 91+ Octane, or any combination of the two.
I haven't yet used E85 as the price is higher than 93 Octane here and it is less powerful... But if you have a Flex Fuel W204 you can use it in any combination you want. According to Mercedes...
Actually, E85 is more powerful and has much higher octane rating than E10 (10% ethanol gas). However, mileage sux and your cost per mile is higher than "normal" fuel. I have found that I get 30% less miles when using E85. So, unless E85 is 30% cheaper (which it is usually not), it is more expensive to use. You can mix E85 with other gasoline. Enjoy reading this:
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
@TimC300 Decode your VIN and check to see if you have Code 929 to know if your car is equipped to use E85. You never know if the fuel flap may have been replaced.
No 929 option. I do have the 917 PZEV Emission which from my limited research on the topic may be the reason why it doesnt recommend E85. When I was looking up replacement parts just to get an idea of cost I noticed the fuel filter/pumps and injectors are different part #'s than non-PZEV engines.
Since we're discussing this again, and I can't resist fuel and oil threads, here is my opinion. On port injected naturally aspirated engines, e.g. M112, I ran 89 octane mid grade, and sometimes 87 octane regular, for 100s of thousands of miles with no problems whatsoever. When I went to direct injection and turbocharged engines (M276 & M271) I ran 93 octane premium almost exclusively, dropping to 89 octane only very few times and then not running a full tank of it. Direct injection engines usually have a higher compression ratio and run with a much leaner fuel charge. Preignition (knock) is never a problem in DI engines because the fuel is not there until it's time to fire the cylinder. But the lean fuel charge and high compression can lead to inaudible detonation which can cause piston damage. A friend who runs an Audi exclusive shop showed me the results of an Audi 4 cylinder DI engine that had been run for years on 85-87 octane regular -- all 4 spark plugs were destroyed and all 4 pistons had visible damage. That was enough to convince me to stick with 91-93 octane in the newer engines.
