rbordel

I don't like to brag, but since you asked...

I've been keeping a log of my fuel consumption of my 2005 E 320 CDI for 3.5 years and about 47000 miles (the car currently has just under 70000 miles on it.) Over that span of time the average fuel economy has been 37.66 MPG, Which I consider pretty impressive. My driving tends to be about 80% highway, usually cruising at 70 mph. This economy was calculated using the (miles driven) / (gallons pumped) technique.

I've attached a graph of the data I've collected. The blue line is the MPG calculated at each fillup. The red line is a sliding average of the last 5 tanks. This tends to smooth out the variability due to not filling the tank to the same level each fillup. I normally let the pump run to its automatic shutoff and do not top off.

On long highway drives in good conditions (warm days with no headwind,) the computer will generally show better than 40mpg over 500 miles, and even higher in optimum conditions. The second attachement is a picture of the car's MPG computer taken at the end of a trip from Birmingham, AL to Fort Worth, TX that I made in March. On that particular day, temperatures were 70-80F and I had a 10-15mph tailwind most of the way.

It's interesting to note that back when I started logging data, diesel was $1.959/gal and fuel costs worked out to 5.8 cents per mile driven. At my last fillup, that has risen to $4.499/gal, or 12.5 cents/mile

As a comparison, I also own a Honda Fit Sport with a manual transmission and have been tracking the fuel economy on it, too. Over a 1.75 year period, its average economy is 39.04 MPG. Fuel costs on a per-mile basis is currently 9 cents/mile.

saffrontiger

Robert, That mileage is outstanding! The highway driving really helps with the MPG. Nice to see another Texan w/ a CDI.
Jay

saffrontiger

Very true. I would like to feel how the 7 speed feels on the hwy considering I have the 05 CDI.

mtetter

Have '05 CDI, 68K. Average 32mpg highway and city. have touched 40 mpg on highway at consistent 75 mph.

terracotta

Hi Robert,

That is very meticulous you have statistically recorded your mileage.
Your car appears to return a good mileage. I am at a loss to understand what may be up with my car. I have talked to blackcdi who is also in the bay area and he feels the air filter should be replaced at this point.

My car has 12,500 miles and it has been thro' the flex-A service. I did bring up the air filter with the service advisor at beshoff motors who said air filter is not replaced at 11,500 miles (the time it was in for this service), he said MB recommends replacing it at 25,000 miles for flex-B service.

I am confused what may be going on with my vehicle. It drives well and everything but I can achieve a max mpg of only 29.

One other thing to note, and that may be an important symptom. I do get black soot deposit on the exhaust pipe. I remember seeing an ad of the CDI where a saleman stuck a sandwich near the tailpipe while the engine was running and ate it - proving how clean the exhaust is on the CDI.

If I run a finger around the inside of the tailpipe I get black soot. Is this normal?

thanks,

-terry

seahonu

terracotta,
What you may be witnessing with the lower mpg, maybe due to intown/city driving. I've noticed the super great mpg (37+) on the highway but once I hit the city streets, the mpg drops pretty quickly. For example, my driving is around 60% city / 40% highway and finding it tough to achieve 24 mpg (my typical). Our CDIs showoff their efficiency at cruising.

rbordel

I think this is not unusual. When I wash my car I notice a lot of soot on the lower rear bumper, and on the tips and inside of the tailpipes.

In normal driving my exhaust is not visible, but under heavy acceleration it is. At night, I can sometimes see my exhaust backlit by following cars even during normal acceleration.

I believe seahonu has a point about city vs highway driving, and around SF I suppose you'll also have to contend with some pretty significant hills, something which is not much of a factor in the part of Texas where I live. You can consume a lot of energy accelerating a 4000 pound vehicle and then turning all that kinetic energy into heat if you drive a lot in stop-and-go traffic. I'm fortunate that on my 40 mile commute to work traffic is such that I can run on cruise control about 75% of the time.

One other thing that I noticed is that when the engine is cold, it is not very efficient, so you pay an additional penalty for short trips that do not allow the engine to properly warm up.

FWhite

A lot of fuel is wasted during low load and warmup operation in order to warm up the catalytic converter. There is a late injection event that increases exhaust gas temperature without performing much useful work.

TPAbnz

My measurements are based on calculating from tank fill-ups. The lowest that I've gotten is 23.5 city, the best 40.5 highway. Averages seem to be 26 city and 37 highway. I agree with the above poster that, at least according to the display, economy is better at 70+ than 55.

As an aside, it's amazing how well the CDI is holding its resale value.

jbec.keane

For comparison purposes only. I have a 2003 E320 with 178,000 miles. My driving is about 70% highway although there is about 10 miles of stop-and-go on the way home.

My summer mileage averages about 28-29mpg. I get about 10% less in the winter when they switch to winter gas.

JK

asg

We have been gettin around 27mpg mixed highway city on a '07 320cdi w/ 18" wheels.

Car has about 20,000 miles on it

CE750

I get 28 with mixed aggressive driving, but this is what makes $4.75/gal diesel attractive to me!

terracotta

How accurate is the dashboard mpg calculator? Do people usual get less actual mpgs than what the calculator shows?

terracotta

Thanks everybody for sharing the data, keep 'em coming in. I observe that people have quite a range of mileage experience. My commute to work is 11miles one way, of which it is about 8 miles of hwy. with this is get about 27mpg.

But I also did a 700mile trip from portland to SF bayarea (overnight driving), at the time this car had 7500 miles and I got only about 30mpg. That is where I think it should have been much higher.

What kind of a minimum distance would be a true test of hwy mileage?

CE750

My one time test of it's accuracy yielded that it was frighteningly accurate!

Untertürkheim

MB's fuel economy calculators were recently rated the most accurate of any make.

musicmax

I've got '05 CDI w/Renntech and have topped out at only 34mpg highway right after a B service and with brand new tires. I don't get it...

seahonu

Whoa, your temp reads 100 deg. Is it that hot out in FL?

Azla

I can get around 33 or 34 doing highway driving and with Cruise control enabled

CE750

I'm running E500 wheels with Continental ContiSport 2's and the temp is 100 degrees which helps efficiency.. it's also at 66mph with cruse control one, but I'm not sure why you're so far off my numbers..

I'm in AZ not FL btw... MUCH dryer and nicer in my view than even a 85 degree in Miami!

aceman

Guys -

How are your cars in the snow? Sorry - don't mean to hijack this thread but with all the CDI posters here figured i'd get a quick answer!

Aceman

CE750

Just spent the worse winter in Columbus OH history with mine and it was GREAT for a RWD car.. nothing like my 4WD X5 would have done, but again.. it's RWD.. I used the C mode on the transmission and it drove and handled well.

Most interestingly, it started right up everytime with less than a 2 second glowplug warmup.

Dieselpowr

Yesterday I ran 60 miles with a 70 MPH average and got 39 MPG, 76 degrees, no wind. Now i didn't reset it till i was up to speed but the numbers are accurate. There is even a 100 ft. elevation increase over that 60 miles so I am running slightly up hill during a fair portion of it.

I am thrilled with the mileage. If you add in stop and go traffic I average out to around 35 MPG realistically with mostly highway driving.

CE750

That's more in-line with most 2005-6 CDI's figures.. I think the new V6 and Bluetech are about 5mph worse however.

edspider

I was getting 21 out of the gas 350 doing suburban driving. When I started hearing that bluetec was only doing 3-5mpg better, I lost interest in it. With diesel running about $0.50 more than premium, it didn't make economic sense to me.