I always thought C mode would give me better MPG so I switched to S mode and see what happen. Now I can easily get 26-27 MPG vs 24-25 MPG in C mode.

a lot of times its the way you drive, heavy foot in low rpm gives the engine more trouble than lighter foot in high rpm given the same acceleration to achieve, thats why it makes sense

I am of the same mindset, but seeing this...I think I'll check out my S mode for more than just gunning it!

I have also found that I get better mileage in S mode and it's a lot more fun to drive in S mode. I have reserved C mode for winter weather conditions only.

This does not make sense actually. It sounds like the same misunderstanding as when a bigger engine is claimed to reach better mileage because it does not have to work as hard as the smaller engine.

You are correctly setting the conditions same, the comparison would not make sense otherwise but if you have a look at the engine efficiency figures, it would give better mileage for the same given power at a lower rpm but higher load.

I've attached an example of an older MB engine, it should give an idea even if the data is not fresh.

For a given acceleration at a given speed you need certain engine power. The figure shows that this power is reached at a higher efficiency at a lower rpm in all typical cases rather than at a higher rpm where the engine load unavoidably gets reduced. This of course only works at the power levels that are reachable with a lower gear (which is always the case if we talk about transmission mode C against S).

My wife just drove 60 miles and got 21 mpg (all highway)

Funny thing is I did the same drive in my family's S550 and got 26 mpg .....WTF

I drive it in C because the smoother shifting. That is about it. Not sure if it should be that much of a difference in MPG though. Ummm

That's really ....not very good.

I typically get 30-31 mpg on my Sunday 200 mile drive. Its almost all highway driving with the cruise control set to 70mph.

Your wife my just not have driven far enough to get a true miles per gallon. Were you using the "since reset" or "since start" figures?

It was since start. I checked at night so I suspect there was some city driving involved. She does not drive with a heavy foot, and even driving on my own very lightly Ive never seen more than 24 mpg. Must be the 4matic....


Edit: btw filled up the night before and it was on 3/4 tank last night so the computer is actually showing higher mpg. (17 gallon tank which means about 4 gallons was used which should have taken me 80 miles not 60)

Geez... I only get 21-22 mpg at best in C mode. Maybe I drive too aggressively. S mode is NEVER better than C, especially on the highway because I believe S mode never sees 7th gear.

lkevinl

Its 1st gear that doesn't happen in "C" mode. 7th gear kicks in at around 53 mph. If you want to test it, drive 55 mph and move the transmission shifter to the left briefly. Note that your rpm increased and your dash display shows 6th gear.

I to have tried both modes when i switch to C mode i get mileage of 27-28 mpg and when i switch to S mode i get mileage around 25 mpg ..

The only thing C mode does is start the car off in 2nd gear. From there, all is the same. Also, if you go WOT from a stop even in C mode the car will use 1st gear. It should make absolutely no difference with MPGs, you're seeing things.

Using "s" mode also causing the transmission to have slightly higher shift points.

I took a nice 80 mile drive out to The Hamptons today sticking my cruise control on 55 mph and on the C mode ...... well was i pleasantly surprised when i saw that i was able to hit an all time high mark of 33 MPG !! Driving back home still using the C mode but a little bit more aggressive drivign at about 65 / 70 mph i was still at about 25 MPG which i still dont think is that bad

Soo with that being said if S mode provides better mileage....... what would've my MPG been in the morning if i was in S and doing 55 mph WOW ??