Hi,
I have a 2003 Mercedez-Benz C230 1.8L Compressor (i.e. it has a supercharged engine). I have been feeding it premium (91) gasoline so far, and am wondering if I can switch to 87/89 grade? Will performance go down?
The manual 'recommends' premium fuel, 91 grade. I remember reading that I can safely user lower grade fuel on most cars that recommend premium, but not on those with supercharged engines.
I live in the San Francisco area, and 90% of my driving is on the freeway.
Thanks for your feedback!
--FOF

 

I do think it is a good idea. Because, if the manufacture recommends 91 octane fuel for your car, it means the engine calibration was developed based on 91 octane fuel to delivery the optimum engine performance. However, as part of engine protection strategy, the engine calibration does have the ability to operate with "bad fuel" in case the non-recommended fuel used by customer, but the engine performance will be degraded due to retarded spark advance to prevent the engine knock. Otherwise, your engine will be generating knock and eventually lead to mechanical premature failure.

Secondly, you think you might save money with low octane fuel, actually, it is not. Because, when the engine operating with retarded spark, the fuel consumption goes up. Therefore, it is not good idea to use non-recommended fuel to save money.

 

This is to continue my previous note since I just realized that you have a super-charged engine. You have to stay with OEM recommanded fuel, otherwise the low octane fuel will damage the pistons. Trust me on this.

 

Stick it with the 91 Octane. I am not with the oil companies but I had proven experience.

I had a Mazda Millenia Type S which had a supercharged engine.

In Iowa where I lived before, there was this 89-Octane gas with 10%Ethanol. It is 10-cents cheaper than regular 87-Octane.

It is veeeeeery veeeeery tempting, so I used it in lieu of the recommended premium gas.

Guess what! After several years of minor knocking and clunking, it killed the supercharger. $4,000 to repair it!!

So, here is my bold statement: ONE MUST BE STUPID TO PUT NON-PREMIUM GASOLINE IN SUPERCHARGED CARS.

I am one of the earlier ones in that line of stupid people.

 

Yeah, stick with premium to avoid engine damage from pre-detonation (knocking). It's the increased compression ratio of a supercharged engine that will cause the problems. Retarding the spark advance helps a little but will not prevent damage in the long run. Unlike turbochargers, superchargers run almost 100% of the time making engine damage more likely. That is, even if you "take it easy" the supercharger will be running and increasing the compression ratio from lower RPM. Single turbochargers usually begin spooling at higer RPM, so unlike a supercharger, you can avoid using it--mostly.

 

Thanks for your replies; they were very informative. I won't be switching to lower grade fuel.
Another point is that I *won't* be saving a *lot* of money by switching, as my mileage will also go down with the lower grade.
--FOF