rubbish m.p.g

[dci120matt]

hi all, just a quick question, when i bought my car the average mpg was 45mpg then after a few months i reset it and my mpg went down to 42, no matter what type fo driving i did, and i reset it again last week and it is now jumping between 36 and 37 mpg, i know you should never trust the computer in the car but i am slightly alarmed, i have about 3k miles before next service will this cure it? thanks

[cactusbob]

What kind of driving do you mainly do?

[nickbell69]

my 1.9 DCI has dropped from around 47 to 42 over recent months. I've been told that colder weather affects MPG.

[dci120matt]

i only really drive it weekends because i have a work van, but i do quite a few short journeys i admit just like popping to the shop and going to the pub and stuff. i probably do less than 100 miles a week in it.

[cactusbob]

Don't forget that you will get lower mpg in winter cos of the diesel mix

[potdci]

I would think it will start to go back up when it gets a bit warmer, i do similar driving to you and im getting 38.6 at the moment but im expecting 43-45 in the summer.

[BurntCarcus]

Ive noticed mine drop to around 33/35 but its preety cold at the minute, never gets above 7d and its 1 at the mo, hope mine goes up lol

[Deano16v]

high 30's around town and short journeys sounds about right, especially in this weather.
when i bought mine the previous owner only used it for school runs and shopping etc so the car was only showing an avg of 35.

[Gav]

Have you put more air in the tyres to compensate for the lower ambient temperature? Running with low pressures will increase the fuel usage.

[dci120matt]

no i have not done that, to be honest it never crossed my mind

[The Negotiator]

Well it shouldn't.

1) Assuming you last checked your pressure at a reasonable temperature, then of course you pressurised it under those conditions, hence relative to that, there is little change. I.e. if you last topped it up at 10 degC, then the current ambient of 7 degC is no difference.

2) Assuming you last checked your pressures at 22 degC and the current ambient is 7 degC, the change is pressure of the air is approximately 5%. That is, if you pressure is around 32 psi, your tyres are actually only at 30.5 psi. Unfortunately, not only do typical pump gauges only read to 1 psi (thus limit of accuracy is approximately +/- 1 psi), but the actual gauges are awful and just indicators, nothing more.

Don't blame tyre pressure differences on ambient weather conditions unless you last topped it up at 50 degC and it's now -20 degC, even then the difference would only be 20%.

[nickbell69]

You took the words right out of my mouth!!

[paul3383]

just like to say i have only had my 1.5 dci for about 4 weeks,
and i get about 47 mpg around town and about 60mpg driving to work and back, 20 miles round trip,
my previous car was an S-Type and use to get about 18 mpg and use to put £50 aweek in petrol and now about £15. unbelievable

[cactusbob]

Correct tyre pressures will help with mpg, but regular checking is all that is required. There is no need to tit around depending on the temperature. Temperature in this country varies wildly depending on the season, weather and time of day. If you want to be really anal about it you could compensate the pressure of the tyres with the annual average temperature - 11 degrees in England (bit lower in Scotland). Its really not necessary, as long as they are about right for the kind of driving you do it will make bugger all difference

[fac51]

My 1.6 VVT sits at a around 35mpg when doing rush hour traffic to and from work. It goes up to 45+ when clear sailing down the motorway which is unfortunately not that often.