GLC300 4Matic very high fuel consumption
Thread Starter
Newbie
Joined: Jul 2017
Posts: 9
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GLC300 4Matic 2017
Earlier suggestion are very good.
can I add the following.
check Tyre pressures, try setting all at 36psi
buy a fuel tank and injector additive, add it to petrol tank and fill up, take care to try and fill as much as possible as you will need to do same technique when you refill normally later to try and obtain same fill level, that way you can manually work out mpg, using fuel added and miles driven.
borrow a hand held, vehicle map GPS unit and measure distance travelled to compare with speedo.
also use portable GPS to compare mph on gps to mph recorded in car, try it at various posted speed limits to confirm accuracy across all driving ranges - can be out by 2 mph I think, any more you may have an issue.
confirm you have minimal load in car and under trunk.
check engine oil levels and radiator while your at it.
my guess is the MAS sensor could be out or air leak in line of turbo, causing too much fuel to be burnt.
what colour are inside of exhaust pipes ? Are they very black and deep soot or fine grey and smooth ?
Dealer really needs to do fuel air mix analysis and download Veh telemetry to confirm
hopefully your brakes are not engaged and constantly slowing you down, lane assist can kick in and brake Veh very slowly if you travel close to the white lines and not in the middle of the road.
still sounds like fuel mix sensor with turbo or injectors malfunction with engine management system over compensating to make car work.
good luck, let us know how your get on.
can I add the following.
check Tyre pressures, try setting all at 36psi
buy a fuel tank and injector additive, add it to petrol tank and fill up, take care to try and fill as much as possible as you will need to do same technique when you refill normally later to try and obtain same fill level, that way you can manually work out mpg, using fuel added and miles driven.
borrow a hand held, vehicle map GPS unit and measure distance travelled to compare with speedo.
also use portable GPS to compare mph on gps to mph recorded in car, try it at various posted speed limits to confirm accuracy across all driving ranges - can be out by 2 mph I think, any more you may have an issue.
confirm you have minimal load in car and under trunk.
check engine oil levels and radiator while your at it.
my guess is the MAS sensor could be out or air leak in line of turbo, causing too much fuel to be burnt.
what colour are inside of exhaust pipes ? Are they very black and deep soot or fine grey and smooth ?
Dealer really needs to do fuel air mix analysis and download Veh telemetry to confirm
hopefully your brakes are not engaged and constantly slowing you down, lane assist can kick in and brake Veh very slowly if you travel close to the white lines and not in the middle of the road.
still sounds like fuel mix sensor with turbo or injectors malfunction with engine management system over compensating to make car work.
good luck, let us know how your get on.
Super Member
Joined: May 2017
Posts: 632
Likes: 57
From: Trumbull, CT USA
Mercedes-Ben GLC300 4Matic
Something is wrong with your vehicle unless you drive with an iron foot, have monster truck tires, or use sub-premium fuel. Overall in 19k miles, with all premium fuel, I’m averaging 25-26 miles per gallon with the 4MATIC, in a combination of city and hill-laden highway driving. The lowest I’ve gotten between fill ups is 22 mpg.
Do you always use the same gas station if so maybe try another one?
Outside of the definitely try to get the dealer to diagonose it . If your dealer is not responding maybe time to go somewhere else
Junior Member
Joined: Jan 2010
Posts: 40
Likes: 4
From: Calgary, Canada
2025 GLC300 4Matic
wow, that is shockingly high, my wife's 2018 GLC300 is in the range of 8-11 l/100km max, in fact it consumes 2-3 l/100 less that my c300 (v6)
