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Hi,

Just wondering which fuel is best. Here in the UK we get either 95 octane unleaded or 98 octane enriched unleaded. Now the brand of 98 I use is Shell Optimax for my other car. To be honest I haven't noticed the difference, but I've been told it boosts the power output of the car in which it is used. Is this true, and if so, will my Merc benefit? I heard somewhere that the big mercs don't like super-rich fuel as it is meant to be too rich for them. Is this so?

Any info'd be much appreciated.

Cheers,

Jason
 

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1995 S600 (sold)
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1,127 Posts
Lower octane fuel can cause an engine to detonate (knock) sooner. This is a bad thing for engines. Many modern cars have knock sensors that will cause the onboard computers to retard engine timing to reduce/eliminate knocking. The problem is that this also reduces power. If you use higher octane fuel, the engine will not have to retard the timing, giving you more power. I did a little experiment a while back using 91 octane vs. 93 octane (I don't know if octatne is measured the same over here in the States, doesn't sound like it). I got less mpg out of the cheaper gas, so using the cheaper gas did not really save me anything. I think the difference in cost turned out to be $1.50 per tankful. I decided to keep using the good stuff. The engine runs better, and the better gas probably deposits less crud.
 

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w140 s300turbodiesel
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238 Posts
The best fuel is the one that's specified in your owners manual. If it says 95 then it's 95 for you which means pretty much any petrol station out there. If it says 97 the same applies. If it says 98 then it's shell, esso and a few others. Don't use optimax just because the commercials say your car would be more powerfull. I have a situation where one of my cars is mapped for 100 octanes and the only place where it runs nicely is in germany where they have v-power (100) and italy (99). But all of this is of no consequence, just use what it says in the manual (or on the inside of the fuel flap)
 

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1996 S600 (Sebastian), 1999 SLK230 Kompressor (Tie Fighter)
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638 Posts
benz has selected the type of fuel you should be using for a good reason. if they take themselves seriously (which they do), then they would not make idle suggestions. my suggestion is that you should take it seriously as well and enjoy your superior machine! [8D]
 
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