Jake of Teesside

Poor Mpg?

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The trip computer can often give a false reading - reset it / use brim to brim figures

AC can drop the MPG and it can come on automatically to defrost/ demist

The engine takes longer to warm up when it is cold outsde, so the "choke"/ mixture enrichment is on for longer, the cabin heater can take a lot of heat out of the system - this heat comes from burning fuel and running the heater can drop the engine temp so it is running in a less efficeint "zone" (worse on diesels - but can effect petrol engined cars too)

More electrical items are on in winter, shorter days mean you must put the lights on sooner/ for longer, heated screens are used, (apparently a heated screen uses a lot of power) wipers etc are used more, all this extra load on the electrical system means the alternator has to work harder, putting more load on the engine reducing economy

If you run your car stationary to warm it up/ while clearing the screen/ brushing the snow off etc this will affect MPG adversely - (the car could have driven miles in that time - how far can you drive in 5/10/15 minites?)

It may be that the 37mpg is correct, and there is nothing wrong with the car

25 years ago, 37mpg would have been a great MPG for a car, especially a car pithe the potential performance of your car, fuel is so expensive now and cars cost so much to run, that it draws attention to the MPG (EG - there was a time when you could put a tenner of fuel in your car and expect it to do 100+ miles on that!) - there is often much talk of 60-70mpg in adverts/ the media - much of which is hype / advertising propaganda - and not achievable in the "real world"

There are things you can do to improve the MPG of any car -

1 - Service it - Fresh oil can reduce friction, clean air filter improve economy etc

2 - reduce weight - get a box and fill it with all the junk you have been lugging around you don't need/ ditch the subwoofer/

spare tyre (get some tyreweld instead) (these are compromises, of course)

3 pump the tyres up to their recommended maximum - this can make the ride harsher but can sharpen upo handling

4 if you have any kind of roof bars/ roof racks - get rid of them

5 Keep electrical load to the minimum - this can be a bit of a "balancing act" - replacing most of the lamps, inside and out, can significantly reduce load - an LED uses approx 1/5th to one 1/10th the power of an incandescent bulb and is often brighter and lasts longer

6 driving technique - simply driving slower does not nessisarily mean better MPG - modern cars can have such high top gears that a higher constant speed may mean a better MPG "common sense" techniques may be counter- productive - some drivers go to extreme lengths (eg - techniques and car modifications ) to get the best possible MPG - its called "Hypermiling"

7 reduce the amount of time the engine is running when the car is stationary

8 AC/ heater - don't let the climate control put the AC on/ leep the AC off as much as possible/ keep the heater off when the car is warming up/ try not to take too much heat out of the system / run the heater up full but the fan low

I hope you find these suggestions useful, they may only add up to a few MPG but it can add up!

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I got a little APP for my phone and have been tracking the MPG now for 82 Days>> Brim to Brim

Miles per Gallon 46.19

Total Cost £720.53

Average cost per Mile £0.14

Total Miles 4872

Thats from a 1.4TDCI Fusion + on a 2005 Plate.

It has a roof rack and ladders on all the time.


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Every time i fill the car i hear a rush of air is this normal? also the fuel gage sometimes drops to half when i have a full tank, 10 minutes or so later it will go back to the full.

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Every time i fill the car i hear a rush of air is this normal?

also the fuel gage sometimes drops to half when i have a full tank, 10 minutes or so later it will go back to the full.

The fuel level drops as it is used, creating a vaccum, (modern fuel tanks are often sealed, to prevent smells/ emmisions due to fuel evaporation, and for safety - way "back in the day" they had breathers to equalise the pressure)

as you open the fuel filler cap the air can rush in to fill the vaccum, it is stonger/ more noticable if you have gone from a full tank to an almost empty tank without opening the filler cap

In this high tech age you would be surprised how "agricultural"/ basic the fuel level meter is -

it is simply a float on a pivot (like a toilet sistern) connected to a potentiometer (a variable resistor - a brush on a carbon track - the resistance is measured by the fuel gauge (an ohmmeter)

depending on the position of the float the gauge may read higher or lower if the car is pionting uphill, downhill or on the flat

Temprature can effect the reading (in all sorts of ways)

even without this the meter is highly non - linear (non proportional - it may be accurate at a full tank (unlikely) but inaccurate at half or empty)

When the gauge reads "empty" it may be just about to run dry or there could be 100s of miles of fuel left

a true "half full" might read as 3/4s or a 1/4 on the fuel gauge

I used to work for Alvis (rent-a-car) (or similar!) the customers were supposed to fill the tanks up in the cars when they returned them, if they were low, they were charged (lots) extra, they could be empty, 1/4 tank, 1/2 tank 3/4 tank or full tank (nothing in between) if it read a little less than full, it was a 3/4 tank

When a car came in (back from a customer) we would check the fuel level, if it was not full on the gauge (but NEARLY full) they would get a surcharge for returning a car with 3/4 of a tank of fuel, we would top the fuel up, often, we only put a cupful of fuel back in a car that was "3/4 full" or we had to brim the tank + the filler pipe untill the fuel was !Removed! out to bring the gauge up to full, - the customers probably only got round the corner and the gauge was at 3/4s again!

Avis (oops i mean Alvis) probably made a fortune out of this (if you add up all the surcharges added to all the "3/4" full cars)

Moral of the story - fuel gauges are not accurate - its just a rough guide

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Can i ask at what revs the 'box changes into top? My 1.6 Auto is reluctant to change into 3rd or top until 2800 / 3000 rpm under medium throttle opening, approaching 50 mph in 3rd; even lifting off doesn't always cause it to change. I'm only showing 32 mpg on a 12 mile journey to work, all dual carriageway (but with 13 roundabouts!). Is this normal: at 30 mph it never sees top gear!

I know that your's is the Durashift, but could this be your problem too?

(My recent Fiat 500 semi-auto would shift at 2500 rpm).

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Sorry, I mistook Duratec for the semi-auto option!


But I would like to know if the late shifting is normal, please.

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