Hope this helps!

I drive a GLC 300 4matic (gasoline) with 18" winter tires when these screenshots were taken for the fuel economy.

Highway - country roads, curves and hilly:
Best 6.6L/100km = 35.6 mpg (USA)
Usual 7.5L/100km = 31.3 mpg (USA)
Most efficient at 70-90 km/h. I can get it down to 5.9L/100km = 40 mpg during at these speeds.

Combined highway (mostly) + city = 8.4L/100km = 28 mpg on my vehicle during the summer with stock run-flat wheels + tires. My winter Michelin X-ice 2s seem to be more efficient, rides smoother and quieter.

Then again, I drive like a grandma despite actually being just 25-years-old. I was also very careful breaking this engine in. There are a few tricks in getting a good fuel economy however.

 

Just got back from a ski trip. Continental snow tires, and averaged 31 mpg. Worst mileage was the slog to from New Mexica from Fort Wrth, averaged 27-28 mpg at 80-85 mph. In ski country at 6500-10000 ft averaged 35 mpg at 50-60 mph. For the 2100 miles, averaged 31 mpg (US, 41 mpg UK). The GLC 300 did great at Altitude.

Anyone know what altitude the GLC300 maintains Sea Level HP???

 

Remember a British imperial gallon is about 20% more than a US gallon.

on my GLC43 in the first two weeks observing:
- 18mpg on short runs
- 24mpg driving smoothly in comfort or eco on 80+ mile runs doing about 70mph

 

To put it on perspective. My 5 yo Ford Escape na V6 awd gets 18 city and 22 hwy and about 20-21mpg combined. It's only 240hp with a 6sp tranny. These are US gallons hand calculated to validate the car's mpg display. If my new GLC43 gets the same mileage as my old grocery-getter I will be very pleased

 

I am not sure if my driving skills are not compatible with fuel economy. I am getting around 15L/100km (~15mpg US) in city and 11L/100km (~21mpg US) on highway.
I don't think I am particularly heavy footed and my service agent is telling me that it would improve after a break in period. Did the OP or anyone see the improvement?

 

What model are you driving, may be an idea to put it on your profile.

 

2017 GLC300. my service advisor said it would get better once i break in after 3,500km or so but not sure lol.

 

Just finished a 2500 mile road trip with a GLC 43 and my mileage ranged from 20-30 US mpg with the average around 26mpg. I drive fast and in Sport mode 90% of the time. My open freeway speeds were 85-90mph. In traffic speed was governed by the traffic volume.

If you are getting 21 US mpg from a GLC 300 there is something wrong.

 

I got 5.14L/100km - 45.8 mpg (US) on a recent 200 mile drive.

Over a three day period I covered a total of 625 miles (1,006 km) and according to the trip function still had enough fuel for a further 98 miles (158 km)......and I wasn't hanging about.

That was about 4 weeks ago when the car was 6 weeks old.

The diesel is pretty frugal.

 

On my 250d the average consumption during my daily commute is 5.9 l/100km (40 miles per US Gal). This route includes highway and surface streets.

Highway only travel returns a consumption of 4.9l/100 km (48 miles per US Gal). Average speed is usually about 120 km/h which is just over 70 miles an hour.

These consumption figures have been constant since new. The car has now done about 19 000 km.

When I tow a 1400 kg caravan, I get an average consumption of 7.8 l/100km (30 miles per US Gal) when driving at an average speed of 95 km/h

 

On last 2 tanks I have got 24 british MPG from 43, really happy with that as only got 31 british mpg from discovery sport 190 bhp diesel.

 

There is quite heavy traffic in downtown Toronto - my average speed as per the computer is 25km/h due to heavy heavy traffic. Would this still result in such a low mileage?

 

Heavy traffic can indeed have a serious impact on fuel economy. While visiting the Seattle area for a day earlier this week, it took about 40 minutes to drive 10 km on I-405 between Lynnwood and the Woodinville exit. The rest of the day's driving was primarily on freeways, with some in-town driving, but the damage to fuel economy had been done. Still, the total at the end of the day was better than the numbers you're seeing. (The car is a Canadian-market 2017 GLC 300, with about 9000 km. on it.)

 

My wife and I just finished a 5300 mile road trip. This included non-freeway travel using the old 2 lane (one lane in each direction) US highway system, in town streets and freeway. We averaged 27 MPG (US). It was very interesting seeing the differences in MPG based on winds, vehicle speed, traffic etc. All MPG in this post were calculated using trip odometer miles and fuel used, not the automatic calculation done by the car although they were close. Our low was 22 MPG heading west on a freeway in Texas cruising @ 80 ish MPH (that was the speed limit). We were fighting a headwind that day. Our high, 33 MPG, was on the Florida turnpike southbound following our son who was towing a travel trailer. Nice windbreak that was. Most of the time the calculations showed 25-27 MPG for any given tank of fuel. Although not significant we started the trip with just over 1000 miles on the odometer and finished with 5400.

 

Filled my 2017 GLC 300 with 93 octane and took a 300-mile round trip up to Maine today, sticking pretty close to the speed limits: 65 & 70 on the interstates, variable on US 1 going through towns along the Maine coast. The trip odometer, which usually reads about one mpg optimistic, showed 32.2 mpg so hand-calculated should yield about 31 mpg.

Very pleased, of course, but one thing that puzzles me is the Bonus Miles in the Eco Display. For today's trip it showed about 90 bonus miles for a 300 mile trip, which seems way over the top to me. I've read the manual and still cannot figure how this number is determined. It must be compared to a baseline that MB considers "normal" or "expected mileage" but I have no clue as to what that might be, other than it must be awfully low to beat it by 90 miles during a 300-trip. Any insights?

 

On second tank of fuel, 928km on the clock - still running in. Getting 11.7L/100km ( 20MPG U.S, 24MPG U.K.). Mainly city driving in Eco whilst running in. Not bad for a V6 bi turbo, pretty happy with that. Of course this will change when im able to get it into sports mode..

 

MY17 GLC300 4Matic
20.6MPG combined
27MPG Highway (75-80MPH)

 

Here is my post from Jan. 2017:
My 2016 GLC 4MATIC now has 15,300 total miles and I've had it for one year. My overall fuel economy is 28 mpg combined. On a trip I usually get 31-33 mpg. My daily commute is about 70% highway driving. I only use Shell 93 octane premium gasoline. Traffic permitting, I drive 5-10 miles/hour faster than the posted speed limit (Valentine One radar detector). The GLC is my fifteenth Mercedes and may be the best one I've ever owned. It is a great SUV!
Update October 2018:
I now have 40,850 miles on my 2016 GLC 300 4MATIC. I reset the trip computer at 15,300 miles and since then my combined fuel economy is 28.6. The GLC is teriffic!

 

I've been tracking on Fuelly for 6500 miles and am at 23.7 combined.

Like other 2.0DIT cars we've owned, the GLC seems to do awesome on the highway and trips, but will chug fuel on short trips or if you get your foot into it too much.

 

Almost 63,000 miles on my 2017 300 GLC now. Overall average for the spring and summer months around 31 MPG traveling mostly at or a few MPH above highway speed limits. I expect it to go down as the weather turns colder.

 

Guys.... i got a GLC coupe 250 Gasoline.... and i do drive in the CITY, thing is even without heavy traffic i never drop bellow 12-13 L/100......

 

my glc350e got 56 MPG (US), mainly city drive.

 

I track every fill-up in a logbook, then transfer to a spreadsheet for analysis. Over 31411 miles, I've averaged 25.5 mpg, with a best-tank mpg of 30.4 and a worst of 21.3. These numbers are calculated from actual miles divided by actual gallons, as the trip computer is consistently about 1 mpg optimistic, as others have noted above.

 

Anyone knows if the MPG can be changed to L Per 100KM? pic credit @dejongj