Poor Mileage 15 Plate Merc AMG C Class- Auto

Daff_Duck · 18 Aug 2020 at 12:11

Just wanted to pick your brains. I have the above with 125K on the clock and recently it has dropped from an avg of 34 mpg in urban areas to 26-28 and I cant figure out why. The journeys are roughly the same and I dont drive with windows down and Tyre pressure is at the recommended levels, not using air-con.. mechanically its sound as had it serviced 4 weeks ago and nothing flagged - I asked garage to take a look at the engine no faults, also checked with my fault meter and nothing shown apart from the usual which can be cleared down.

So what gives, any ideas..

MrRockliffe · 18 Aug 2020 at 12:13

Is it a diesel?

sovietspybob · 18 Aug 2020 at 12:21

Look for a sticking brake caliper, see if any wheel is warm after a decent run.

Daff_Duck · 18 Aug 2020 at 12:58

Thanks for the brake caliper idea, sorry, its a petrol

Greebo · 18 Aug 2020 at 13:16

Check the air filter. I once had my car serviced at main dealer and my economy plummted afterwards. Turns out the dealer had left a cloth wipe they had used to clean out the air filter box when changing the filter and it was blocking the air intake and the car was running rich all the time.

[TW]Fox · 18 Aug 2020 at 13:21

27mpg urban from a petrol automatic C class sounds excellent. 34mpg sounds unrealistic.

ShiWarrior · 18 Aug 2020 at 17:29

thats good mpg to me ?

i get 28 mpg for a 2009 1.8 focus petrol manual

IAmATeaf · 19 Aug 2020 at 10:07

sovietspybob said:
Look for a sticking brake caliper, see if any wheel is warm after a decent run.

This, my sons Golf gave pretty poor MPG, my son just accepted that it was probably just a combination of the car and his driving style but it wet in around 7 months ago to have the discs and pads changed all round and they found that it had sticking calipers. After the change he noticed an immediate improvement of 4-5 mpg.