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    (It's a 2015 Mercedes C220 Auto 7-Speed)

    When I started driving the car, I was getting between 65-80mpg on the main A roads, down to 45ish on town, and up to the 100ish mark on motorways after 20 minutes or so.

    Now, I'm lucky to get 20 in a town, the most I've managed on the A roads is 40, and even that's with coasting in neutral on half the time down the hills and such like which I wasn't doing before, and I've never achieved more than 60 on the motorway.

    Not using AC or any other thing like that, it's just got really bad economy in the last few weeks.

    The display shows the tyre pressures as normal, and there haven't been any payload differences.

    What could cause a new car to suddenly start using more fuel?
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    Surely if its new and under warranty, then you take it nack and get then you get the Mercedes people to sort it out?
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    (Original post by 999tigger)
    Surely if its new and under warranty, then you take it nack and get then you get the Mercedes people to sort it out?
    But I don't know what the problem is to start with!
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    (Original post by XMaramena)
    But I don't know what the problem is to start with!
    I'm assuming you bought this new or under warranty. Just pop by the dealer. You have a probkem with fuel economy, although you need to check what you are getting now is below what they advertise it will do.

    If you are getting poor mpg, then you need to tell them and its their job to check it and fix it. Thats what warranties are for. they should give excellent after care serbice, thats why you pay a premium. they are the experts, they might know the answer straight away or they can do diagnostics.

    Because its new then the responsibility is their to fix it if it is defective.
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    (Original post by 999tigger)
    I'm assuming you bought this new or under warranty. Just pop by the dealer. You have a probkem with fuel economy, although you need to check what you are getting now is below what they advertise it will do.

    If you are getting poor mpg, then you need to tell them and its their job to check it and fix it. Thats what warranties are for. they should give excellent after care serbice, thats why you pay a premium. they are the experts, they might know the answer straight away or they can do diagnostics.

    Because its new then the responsibility is their to fix it if it is defective.
    Not sure how to go about it, since I'm just a named driver on my dad's company car. But my dad is the worst person for sorting things out. He went 4 years without washing a new BMW 320d. It was disgusting by the end of it.
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    (Original post by XMaramena)
    Not sure how to go about it, since I'm just a named driver on my dad's company car. But my dad is the worst person for sorting things out. He went 4 years without washing a new BMW 320d. It was disgusting by the end of it.
    Just ring the dealer up. They might give you a quick bit of free advice if its an obvious problem. they might challenge you about being the owner, but you cna say your dads asked you to sort it out. Presumably its his car and company?

    They might ask for the log book to verify you are the owner/ person allowed to drive. Its not a big deal to sort out if you think there really is a defect..
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    (Original post by 999tigger)
    Just ring the dealer up. They might give you a quick bit of free advice if its an obvious problem. they might challenge you about being the owner, but you cna say your dads asked you to sort it out. Presumably its his car and company?

    They might ask for the log book to verify you are the owner/ person allowed to drive. Its not a big deal to sort out if you think there really is a defect..
    May press Info button for it. We have MBrace as part of our lease, and Info button could mean things like this. Not sure though, so been wary of pressing it in the past.
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    Just ring customer care for your dealer or mercedes and see what they say. You should have some proof of ownership documentation pr service manual somewhere. You will need to check that the mpg you are getting is below the spec.
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    Not sure if it actually happens with this model but perhaps the ECU has adapted to your driving style, resulting in lower MPG. Although your initial stated figures are too high anyway.
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    There is no way on earth you were ever getting 100mpg even on the motorway. How have you worked out these figures?
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    If you're going by the readings on the dash, it is probably inaccurate to start with.

    Best way, brim up the tank, drive 100miles or so then brim it up again. Do a calculation, if it is indeed true you're using more fuel then before, try resetting the ECU.

    Also have you changed brands of fuel recently?
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    (Original post by KCLeblanc)
    There is no way on earth you were ever getting 100mpg even on the motorway. How have you worked out these figures?
    I assumed he meant k.m.
    It shouldnt be too hard to look up what the stated fuel economy is and then compare them intelligently to what you have.

    Alternatively ccontact the people you paid ££££££ for it and use their knowledge to identify whether there is a problem and fix it.

    Cant see why this is so hard.
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    The only things I can thing of that get 100mpg are 125cc motorbikes...
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    Yeah, if it's a petrol then those latter fuel economy figures seem more accurate IMO, maybe a little low but not massively so if you have a heavy foot. Also, you shouldn't coast, but that's another topic for discussion Do as another poster said and work out your economy the proper way - brim the tank, do some driving, brim it again and compare the litres used the second time against the miles driven. With some basic maths you'll get your economy. Far more accurate than the on-board computer any way.
 
 
 
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