MPG
 

Hi all: I am new here. I live in Boston and have an 2008 S550 with 224,000 miles on it.

Can anyone tell me the best possible MPG one can get on a highway?

I was hoping for 24 mpg but I am concerned that I might be fooling myself. Also, do you use 93 octane or 91 octane? Any help here appreciated.

One more thing; I was told that the rear wheel drive 550s rides more smoothly than the 4Matic because it does not bite the road in front as it is simply being pushed from behind? BTW, I love this car.

Thanks!

S550 uses (at minimum) 91 octane gas. It's the S600 with the V12 that I believe requires 93.

My 2008 S550 gets me just under 10L/100km (approx 24 mpg) on highway at cruising speed of ~120km/h.

My 2008 S550 averaged 28 MPG on a round trip from Phoenix to San Diego this year (140k miles on the odometer). The high MPG was 30MPG at 75MPH, which considering my wife and two adult sons were in the car ... seemed pretty good. It's great going to the beach without filling up along the way.
https://cimg8.ibsrv.net/gimg/www.mbw...197bd5e900.jpg

Not sure how the older generation of the engine can get better mpg than the new turboed engine in my 2013 s550. The best I've seen is 8.7L/100km or 27mpg on mine.

All I can say is WOW! I would be thrilled to get that. Tell me, do you use 93 octane?

No, just the 91 RON at either Costco or Chevron. I do stick with Top Tier fuel. https://www.toptiergas.com/

Thanks so much my friend!

I'm confused., are you saying Costo gas is better than others?

Costco Wholesale and Chevron are listed in their list: https://www.toptiergas.com/licensed-brands/

That means they adhere by the fuel quality standards listed there, which means, in theory the fuel should be better than other stations that are not listed.

Oh, that's good to know, very cool. Recently, a few times I got gas at Sheetz and Pilot stations, and the one time I swear I got less miles to a tank. Wonder if that could be the reason or just coincidence?

I hate when they add the oxygenated stuff to the gas here for the winter. You always get less MPG and it sucks.

Just got 26 mpg on trip to Boston with AC on, that means I'd get more with it OFF. I would think w222 would be similiar. 35 psi in tires. Make sure yours aren't low. To me, that's incredible gas mileage on a NA car!

The owners manual states to use 91 octane minimum, and if you have to use 87, only fill half the tank with 87, until you can fill up with 91 again. Running 87 octane in an S550 is like drinking Sutter Home wine at Morton Steakhouse.

Usually get about 26mpg in my 550. There was a time where i got 27.1.
also its easy to get high mpg if you only drove 10 , 15 , 20.. miles. To say that you get a good mileage and accurate you gotta drive id say at least 50miles , the more the better and more accurate.

So here's the funny question. I wonder if the NA engine gets better mileage than the Turbo'd one.... The EPA figures for the NA engine on MPG are way off and underestimated for sure. I realized that as soon as I got this car, way off. In a good way.

Well along those lines I was wondering if the direct injection on the M278 (turbo engine) would over time lead to lower MPG due to carbon buildup common with direct injection engines...

Just for reference on the MPG, I observed 28MPG for the round trip from Phoenix - San Diego - Phoenix, about 700 miles. Keep it running, do ALL the maintenance, keep the tires aired up. Honestly it's an amazing machine.

That's the issue with the M278, haven't had high mileage ones out long enough to know, BUT, this is true. Turbo's do go bad, and when they do, thousands $$$, and if just one goes bad, you really need to replace BOTH as a pair. Mercedes screwed everyone on the used market, and I think over time, while Mercedes thought making smaller engines, that aren't as heavy, etc, will bite them in the butt with huge repair bills.

Thanks for the response and the information. As an aside, I love Mortons!

You are right. I read this last night and decided to drive to see my brother in Maine. 200 miles round trip at 75-80 mph. Got 24.8 mpg.

I think that is OK.

I am not unhappy with that.