Do i have to fill up my 550 with the premium gas ?

 

yes. why wouldn't you use premium on a 100k car

 

good point

 

I believe it says to use premium fuel on the sticker inside the gas cap.

 

What he said... Seems like it would be an obvious choice.

 

if you do use good ol regular, update us on its performance.

my thinking is that before purchasing the S class, one would know about the mileage & premium gas so why fret over it?

 

Only premium gas should be used.

 

What is premium gasoline in the United States? In Europe we drive with regular gasoline. 95 octane

 

Premium is 91 or 93 octane depending on which part of the US. In California it is 91.

 

The two Infinitis I've owned both stated clearly in the manual that Premium was recommended but not required.It went on to say that use of 87 octane would cause no damage to the vehicle but would result in "reduced performance".MB,OTOH,*requires* Premium in all gasoline vehicles it sells in the US (although I think some can take E85).Why take the chance with anything less than Premium? A couple of dollars a tankful is what you're talking.

 

different measurements.

RON in europe, R+M/2 in the us.

 

2 yrs ago I switched to unleaded 87 octane on my S550 and the only thing that happened is my milage increased 2 to 3 mpg..

 

Interesting....Higher MPG sounds counterintuitive...would love to hear your current MPG and previous Premium MPG?

Also, I've read that regular (87) tends to create more carbon build-up than Premium (91+) but some gases with detergents (exxon/Chevron/shell) mitigate that.

Aside from the extra gas mileage, have you noticed any other effects long term, both good and bad?

 

Maybe its just me, others may not notice the difference, but why buy S550 and not enjoy it to its full potential. it might run fine on 87 but you're not getting the smoothness and power that it truly built to provide.
If you're using 87 because of gas prices, you might want to look in to S350 or perhaps a lighter car with smaller engine.

 

I've got a friend who drives a C350 coupe and only puts in 87 octane gas. There is a unquestionable knocking sound when there is a load in the engine, say going up hill or sudden rush of gas into the engine (aka flooring it).

 

I get a knock (under heavy acceleration only) using the California Premium (91) from Chevron. Can't imagine with 87 would do to it.

 

The owners manual states to use 91 octane mininum, and if you have to use 87, only fill half the tank with 87, until you can fill up with 91 again.

 

I only use top tier gasolines not that I think it's necessary, but it's recommended on the bmw 750 and has always kept my bimmers free of carbon build up and very powerful.

 

I use premium 93 but dont touch anything but Mobile or Shell. I know these 2 might not be the best but somehow both my S550 and CL600 respond best to these 2.

 

Actually both of those are top tier gasolines, including: Chevron, Exxon and a few others. They just add a cleaning agent I believe its techron not sure but hey they are highly recommended for many high end cars.

 

I accidentally filled up with regular the S550 started to knock. I was down to a quarter of the tank and as soon as I was able I added more Premium. Now that the tank has been refilled with premium it does not knock

 

Do you mean "decrease"?

 

Stay away from cheap premium gas. WalMart etc. Those type sellers are cheap not because of volume but because elective additives are omitted in the "WalMart recipe" refinery blend. Stay w Chevron, Exxon, Shell etc.

 

Some interesting info...

I just had a discussion with a guy that's had 4 S classes and has only put 87 octane in all of them.

Also, his friend that owns a Mercedes dealership, and 3 other dealerships, put 87 in every Mercedes they sell when they put a full tank of gas in your car at the dealer at the time of sale...

 

87 can give you better mileage
The difference in the octanes are the rate at which they burn -
A the higher the octane the faster it burns -
This is the reason you get lower performance from lower octanes
High performance engines should use higher octanes
Also the timing on the cars specified with a certain octane are set to that octane
This is another reason you can get knocking from lower octanes

Hope that helps
I have a viper and s63 and I use premium - my wife has a Lexus gs 300 and she drives it very slow and we use 87 even though it says premium - no knocking at all w 126k miles - if she had an s550 I would use premium as it is a high performance car even though she would still drive it the same way
Your preference but hope this helps