thaeni

I have a 2012 C250. When I use 91 octane I get allot better gas mileage than when I burn 89 octane. Just wondering why this would be ?

xsever

Because these engines are made and optimised to run on premium gas which is 91 or above in the North America. It says it in the manual. Running lower octane gas in them can cause you trouble on the long run.

dannyboy42670

If you care about gas never go muffler deletes.... I average 15.1 MPG on a good day..... :p

Carsy

Why would deleting a muffler give you worse mileage?.

In older cars it used to give improved exhaust flow & better mileage.

dannyboy42670

Some argue that the cats and resonators hold the back pressure, but a loss of back pressure can be felt with the muffler deletes; where -pressure = -MPG

Alfadude

Can't say I ever heard that. I would think that if doing that by itself would affect the mileage that would mean the engine would not be running as efficiently as it could and if that would be the case I would think you would get a check engine light. Maybe just more inclined to floor it more often than before now that it is louder. That would increase the mileage more than anything.