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Falling MPG any ideas?

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  • Kev27
    Kev27 Posts: 394 Forumite
    Part of the Furniture 100 Posts Combo Breaker
    edited 17 November 2014 at 3:14PM
    Throw a bottle of Cataclean in the tank mate and give it a good thrash up the motorway, might just need a clean out.

    http://www.eurocarparts.com/ecp/p/car-accessories/engine-oils-and-car-fluids/car-additives/fuel-treatment/?542770410&0&cc5_169
  • Strider590
    Strider590 Posts: 11,874 Forumite
    edited 17 November 2014 at 3:22PM
    Mr_Mink wrote: »
    Stryder
    The heater sadly has never been the quickest (I've always just attributed that to the poxy little three-pot engine in it). Is checking the coolant thermostat an easy enough job to do or am I better off sending the car to the garage for that to be checked?

    It's simple, start the car, let it idle until it's warm, go for a drive, if the engine temperature drops more the faster you go, then the thermostat isn't working properly.

    They don't last forever, they're basically a valve with a small piston filled with wax, which melts at a given temperature, forces the piston open and allows engine coolant into the radiator. It then opens/closes the whole time your driving to regulate the temperature.

    I replaced mine a few months ago and went from 33mpg to 38mpg.
    “I may not agree with you, but I will defend to the death your right to make an a** of yourself.”

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  • alleycat`
    alleycat` Posts: 1,901 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    As previously mentioned.

    When was the air filter done and was it done "properly".

    After the last service on my dads c-max it was "crushed in" and the car was running less than optimally.

    Re-seating it made the car run much better.

    Likewise what tyres have you had had fitted? Are they like for like and are they correctly balanced.
  • Mr_Mink
    Mr_Mink Posts: 264 Forumite
    Ninth Anniversary Combo Breaker
    On the tyre front I've gone from Continental Premium Contact 2's to Nexun N-Fera's, according to the fuel consumption rating they're both a 'C'. But there was still this constant decline in mpg whilst I was on the Conti's e.g. last summer 62 mpg to this summer 54 mpg.

    As for the fitting, I get my tyres done at a place owned by the company I work for's sister company so they tend to take good care of us when doing any work. So far nothing seems untoward on the wear front (the little wear that there is anyway) and again wouldn't explain the issue also being present when looking at a summer to summer comparison.

    I had considered some sort of juice for the tank and a bit of a thrashing but wasn't sure if that would be of any use for this car?
  • Mr_Mink
    Mr_Mink Posts: 264 Forumite
    Ninth Anniversary Combo Breaker
    Strider590 wrote: »
    It's simple, start the car, let it idle until it's warm, go for a drive, if the engine temperature drops more the faster you go, then the thermostat isn't working properly.

    They don't last forever, they're basically a valve with a small piston filled with wax, which melts at a given temperature, forces the piston open and allows engine coolant into the radiator. It then opens/closes the whole time your driving to regulate the temperature.

    I replaced mine a few months ago and went from 33mpg to 38mpg.

    I'll give that a go. I'm going to go ahead and guess that if it is the problem it's a wear and tear issue.
    alleycat` wrote: »
    As previously mentioned.

    When was the air filter done and was it done "properly".

    After the last service on my dads c-max it was "crushed in" and the car was running less than optimally.

    Re-seating it made the car run much better.

    Likewise what tyres have you had had fitted? Are they like for like and are they correctly balanced.

    The air filter (I think, need to check the docs I have a home to confirm) was done at the 30,000 mile service which was about 4 months ago. It was done at a VW dealership though I know that's no guarantee of a job being done properly (this is the second dealership I've used after the shoddy job/everything the first dealership I used did).

    Tyres wise, I was explaining while you posted so is in my previous post.
  • alleycat`
    alleycat` Posts: 1,901 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    Mr_Mink wrote: »

    The air filter (I think, need to check the docs I have a home to confirm) was done at the 30,000 mile service which was about 4 months ago. It was done at a VW dealership though I know that's no guarantee of a job being done properly (this is the second dealership I've used after the shoddy job/everything the first dealership I used did).

    Yeah my dads air filter was done at a ford dealership so it's not a guarantee of good workmanship sadly.

    Needless to say they've not had his business again.

    Does that previous service tie in with the "drop off"?
    Did they do any software / ecu updates to the car?
  • Mr_Mink
    Mr_Mink Posts: 264 Forumite
    Ninth Anniversary Combo Breaker
    alleycat` wrote: »
    Yeah my dads air filter was done at a ford dealership so it's not a guarantee of good workmanship sadly.

    Needless to say they've not had his business again.

    Does that previous service tie in with the "drop off"?
    Did they do any software / ecu updates to the car?

    I kind of wish it did because at the last service they had to replace and reprogram (how you do both I don't know) the ECU. Well, I say at the last service, they reprogrammed the old one then had to get me to take the car back a few weeks later to replace the ECU. Really fills you with confidence eh.

    But sadly I've been seeing this decline over the course of a year to a year and a half which is what has made pinpointing any specific event as the problem rather difficult since in that time I've had it serviced twice, a new ECU, new tyres on all 4 wheels and new front brake disks and pads and just this continual (quite steady) drop in mpg the whole time.
  • Ultrasonic
    Ultrasonic Posts: 4,265 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Photogenic
    Due to wear, the circumference of the tyres is now smaller which increases the number of revolutions per journey. This will increase the fuel consumption.

    Are you referring to the trip computer indicated mpg or the real mpg there?
  • EdGasket
    EdGasket Posts: 3,503 Forumite
    Due to wear, the circumference of the tyres is now smaller which increases the number of revolutions per journey. This will increase the fuel consumption.

    I'll get some bigger wheels then, will save ££'s now yay!
  • Something that's not been picked up on as far as I've noticed - you say you had new brakes fitted. If the pads were fitted incorrectly or perhaps were too tight in the caliper/carrier, it's possible you've got a bit of brake bind


    After a decent run and some brake usage, feel the wheels with your hand and see if they're all the same temperature. If one's appreciably hotter than the others, may be that you've got a sticking pad/caliper.
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