hello everybody,

first of all thanx for the replies...

I have w209 clk 200 kompressor, 2003

in turkey we have 95 and 97 octane gas do you know which will be the most recommended for my car?

97 Octane RON

i always try to go for the highest octane. we're lucky here in Australia to have a 98 octane petrol.

Note that lower elevations require higher octane, where higher elevations get by with lower octane. Here in Birmingham, Alabama (USA), we are about 650ft above sea level so we get 92/93 as our highest octane (R+N/2 method). Our friends in Denver, Colorado, elevation 5,000ft+ get only 89 octane as their highest. And that's all that is necessary as thinner air equates to lower PSI in the cylinder during the compression stroke. Octane is all about preventing early combustion do to the heat from the higher pressure levels in the cylinders of high-compressing engines (refer to Boyle's Law).

But dont mercs require at least 91 octane? I was under the impression that the higher the octane, the cleaner the petrol, hence the better it burns, the cleaner your engine will be and the better consumption youre gonna get.

The US uses AKI to state octane as Rudeney explains. Europe, SA, Australia etc state research Octane number or RON on the pump hence the higher number.

Octane has nothing to do with fuel quality. It is purely a measure of a fuels resistance to knock, preignition, pinging, detonation by whatever name you know it. Octane requirements typically rise as an engine fouls itself. Octane requirements drop with altitude as Rudeney has explained.

ok thanks for all the info. what about the E10? would that work with my cars? 04 CLK240 and 03 E320. cheers!

Only use E10 or other alcohol fuels in your cars if they are flex fuel cars. Otherwise you could suffer corrosion in your fuel system which can get expensive. That said most Benz cars will tolerate E10 or 12 but not more.

We have no choice here - our fuels are always E10 (10% corn-derived ethanol). This is our government's strategy for (1) subsidizing the corn industry, which is very rich and powerful, and (2) making people feel better that 10% of their fuel is "home grown" instead of imported from Middle Eastern countries.

The FlexFuel rated cars can run on E85 (85% ethanol) but few people do that. Even though E85 (when you can find it) is a little less expensive than "gasoline", it only gives at bet 60% of the power and fuel economy of gasoline, so it's not such a good deal in the long run.

thanks Glyn and Rudeny! also, would there be a significant change in performance since im used to 98 octane on my cars if i use E10? and would there be a long term effect on the engine or fuel system and what not? appologies to the OP. no thread highjacking meant.

Ethanol has 2/3 the energy content of gasoline, so E10 would only have you losing about 3% in efficiency over 100% gasoline. It's all we get over here and all the C240s seem to be just fine with it.

thansk again gentlemen! will probably alternate 98 and e10. or is that bad?

Thanks specially Glyn and also thanks for the other replies.. I was using 97 octane for my car but my service said that there is no need for 97. they recommend 95 octane.. Im not sure but when I use 97 octane I can feel that the performance of the car boosts? am I wrong may be it is psychological

97 Octane will give you better performance for sure.

baybarda, since Rudeney mentioned it, i tried E10 the other day and its not much of a difference from 98 octane that im used to...performance wise. there is a difference of course but i reckon its more psychological (for me anyway).