jstaneff

Well, I've been wondering ... and this conclusion may be wrong, but it's a step in understanding what's happening.

As we all know, the trip mpg is a cumulative computation from the preset initial value, depending on how you drive. On a trip of about 35 miles, I can easily get it up to a 28 mpg reading. On slightly longer trips I can get it to the 30-32 mpg range. (All in the C-300.) Most, but not all of this is highway. Yesterday I got it to 27 mpg on back roads averaging about 35 mph.

But the things is, it keeps on climbing. It's almost as if there's no maximum. Sure it may take a mile to get another 1/10th mpg, but it does come. Of course some factors limit this, such as rain (drying brakes with with wipers going?).

Today I was low on gas, so switched to the screen where it shows miles remaining. It stays this way until you reach the 1 gallon left mark where upon the "feed me" logo pops up and stays. When I immediately switched to the trip screen, I had 28 mpg. Four miles later when I got gas, it was at 29 mpg.

Watching it carefully, I was seeing 35 miles remaining when "feed me" appeared. So, does this mean that the instantaneous mpg at highway cruise, with the engine fully warmed up, is 35 mpg? Cool.

My guess is that's close. I still haven't taken this car on a long trip, and I know that some factors are strange (like it gets better mileage on a full tank ... heavier, closer to the ground, less frontal area?).

Anyone have similar observations? Anyone add anything to get instantaneous mpg on their 2008 C?

micropower99

Mine goes to a maximum 25 mpg Is yours 4Matic?

jstaneff

Nope, straight 2WD/RWD.

ShoremNJ

it's an anomoly, C300 just doesn't get 35 MPG unless you go downhill all the way coasting in neutral.

rb23lb

i can get 32-33 in my c350 on long trips in cruis control at 65 mph... pretty consistently too...

not bad for such a heavy car...

mat2hu

i've gotten around 32-33 MPG on a CONSTANT going 60 m.p.h the 7-speed really helps in the freeway because it keeps your RPM low and consistent. i believe i could even reach up to 35 mpg if i had been driving farther. BTW this is in a C350 not a C300, so in a C300 you could do slightly better also, or at least you should be able to.

ChopStickPhobic

never got over 30 mpg on my c350, but got close, 29.4mpg, i was cruising for the most part, but hit 120mph for a couple of sec because some a-hole driver in a jeep.
http://photos-f.ak.fbcdn.net/photos-...48509_6854.jpg

tanktube67

The best I got is 28 mpg

jstaneff

That's yet another question I have about how this car computes it's trip mpg. I'm informed, from another thread on this forum, that the 7-sp does not "free wheel', so it would be difficult to get great gains from driving downhill.

I do sometimes hit a downhill, and I can back off the gas, but the car is obviously using engine braking/compression and does not 'take off', but rather holds speed on the descent. That suggests it won't get great mileage from the descent, but it can raise the trip mpg about 1 mpg for about a mile of descent.

I understand that with the foot off the gas, the engine rpms will not cause gas to flow into the engine ...

mat2hu

BTW when i am saying that i got 32 MPG, it wasn't all downhill. It was mostly flat and some parts downhill and other parts uphill. It was a total mix and even one part was semi-steep uphill for about 4 miles but then it was a slight downhill after that for about another 5 miles

orie

the best i've been able to get a long road trip (6hrs) was around 28.2.

speed varied..probably averaged 65-70mph

orie

i've never sniffed anything close to 30 though

cdye12

I do 40 miles roundtrip per day and I usually average 23-25 MPG mostly freeway going around 75 MPH. With the recent Kleeman ECU tune I've checked the instant mileage while doing 70-75 MPH on the freeway for approximately 5 miles and I averaged 28-29 MPG. This if for the 09 C350, for reference, I'm running the stock conti's (for now) with 18" C63 Rims.

kimyoung_k

Nice..

Most I got from crusing at 70mph with My C300 4matic is 27mpg at 6000miles

Nuru

I can get 26+ mpg and I have a 4Matic, and that is on a 30 mile trip