Does do C350 really needs the Premium fuel or should we go with the cheapest? Im using the cheapest and the engine seems to work fine. What do you guys think?

2008 C350 4matic

I average 29-30mpg on the highway at 60-65mph.

On the non premium fuel issue - modern ecus will adjust timing and mixture to prevent knock due to differences in fuel characteristics, so using regular instead of premium won't damage your engine - but you won't get 268 hp or the published mileage figures either. It'll make less power and increase fuel consumption, so you won't be any further ahead.

Running a lower than required octane can cause engine damage from preignition and carbon buildup. Plus, the losses to fuel economy will cost more than the premium fuel. If you can not afford the fuel, you should not be driving the car.

<<<6. Let off the gas and coast or put in neutral when heading towards red lights or stale green lights. Why have your foot on the pedal or the cruise on when you are going to be stopping anyway. >>

If you think this saves gas, you should learn something about modern fuel injection.

When you lift off the gas pedal when slowing, fuel flow stops, resuming when idle speed is reached. Even my 25 year old Porsche's Motronic system does this.

Therefore, you are using more fuel, not less, by coasting in neutral because the engine will be idling and using fuel. This is also illegal in most jurisdictions because it's unsafe.

I say use premium. the 20 cent different is a tiny percentage of gasoline price these days. Just find a more affordable good name station to help make up the difference.'

Why not have the car perform and run as intended? $100 bucks a year if you use a tank a week like me or something, not worth it.

Isn't the octane higher in Europe? I know in Holland regular is 95 and super is 98.
It will make the car run a little warmer and help with fuel consumption.
My friend in Holland told me he just paid $1.67 for 1 LITER of regular. That's like paying almost $10 for a Gallon!!

No. They just calculate octane differently. 93 us is about 98 European

I had my C350 in for it's 26,000 mi service last month and the damn dealer reset my trip computer! Pissed me off. Another thing that REALLY pissed me off - i went out today to check my tires and the original tire valve stems that came with my C350 were gone. There are now cheap gray plastic ones on there. I'm positive someone at the dealership did it. A regular thief would not have replaced the stems! If any of you would do me a favor and post a few pics of your original C350 tire valve stems, I would appreciate it!

Here are the current readings since the reset. I have to say that I drive my car much more normally than when I started this test. Now I just drive it to have fun and really pay no attention to the MPGs. So 24.1 MPG avg is pretty darn good for a car that has 17/25 on the sticker with a 20 combined MPG avg.:

4123 mi
24.1 MPG
111:04 h
37 mph avg.
total mileage on car: 27,808

Gray plastic valve caps are standard from what I have seen and are what is on my car. What did you think your old valve caps looked like?

Since this thread was re-hashed I'll comment on this as well. You can use lower octane but won't get the best performance from your car. Notice the "recommended" octane notice for your car but it's not a must. Your ECU will just pull timing(loss of horsepower) if the lower octane causes detonation under certain conditions. Your motor will be fine as it pretty much takes care of itself but again you won't get the best performance from your motor and some people think what's the point of buying a car with "X" amount of power if you can't achieve it by running cheaper fuel.

As far as feeling the differences in power that will all depend on the conditions and how much timing is pulled. If all you do is light acceleration and cruising then lower octane is fine as there will be no difference.

They were sort of silver colored plastic, and longer than normal. They were much better quality than the cheap gray plastic ones that are on there now.

In the city I get about 25.4 mpg, but in a highway 500 miles trip it hopped to 32.2 mpg.

guys i have 13mpg is it normal ?

My 08 averaged this on a trip today.