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Active Member
Aug 29, 2003
A180cdi Avant Garde
I just heard on Radio 4 that Which magazine has published a report comparing 3 "superfuels", two petrol and one diesel brand, to the standard versions. Their conclusions were that there were no significant differences in either performance or economy. Have not found a link to this particular report yet, but found a similar article from What Car last year with similar conclusions:

I suspect, with current high prices, we may be seeing less of these fuels.
I know a few people who have tried it with bikes and maxi scooters and came to the same conclusion.
I've used a variety of enhanced diesel fuels and haven't noticed any significant increase in performance or economy although the engine is smoother and quieter so I'm happy to continue for this benefit.
the article i read this morning did mention that in the long run those fuels are probably better for the engine and should result in lower repair bills (on average)
When these fuels come into their own is in highly tuned supercharged or turbo charged engines with ECU's capable of adaptive behaviour. :) This is usually a function of ignition timing and variable boost pressure when certain constraints are applied to stop destructive phenomena such as pre-ignition. :eek: Higher octane fuels extend the range of engine performance slightly which can lead to greater efficiency= power generated V the thermal energy in the fuel.:bannana: This can lead to slightly better MPG figures but most drivers tend to exploit this benefit by using the extra power released instead. ;) To put it another way, if you drive a Subaru Impreza or an AMG Mercedes you may well experience a different driving experience with the higher grade fuel but if you drive a normally aspirated Mercedes saloon/estate/4x4 you probably won't notice the difference.:crazy:
I not so sure if we will see less of these fuels since the manufacturers seem to be moving to smaller engines capable of a wider performance range by supercharging,turbocharging or both, to replace larger displacement engines in their bigger cars. These may well demand higher octane fuel like the new direct injection petrol engines.;)
The day Mercedes start recommending them, I will use them.

Till then I remain convinced that the benefits as Which and What Car found are largely psychological.

As for adding fuel additives ourselves this is what MB say: -
"Do not use fuel additives, since they can lead to increased wear and damage to the engine. If you use special fuel additives this will limit your warranty entitlement." Page 388 from the E class handbook.
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I was told in no uncertain terms to only use high octane fuels 98ron or higher in my car.

Only if desperate then put normal unleaded in.

That was from the AMG guys at the factory, so thats what I'm sticking with...:)

I was suprised at this but having said that a freind of mine has a V10 M5 and only put the cheap unleaded in until I told him about what AMG had said so he has tried the super unleaded and now he reckons his mpg has gone up from 19/20mpg to 24/25mpg, he's happy.....;)


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