Winter Fuel Economy (Diesel)

[MondeoMan1981]

Does fuel economy tail off a bit in winter?

Since the start of the really cold snap here in Scotland I've notice my mpg dropping. Not just when sat in snow traffic obviously, but generally.

Had the joy of running in -12 last week and most of my running now seems to be split between -4 and 3 degrees!

[sparks_E39]

It effects most cars, my petrol car takes a bit longer to warm up, therefore my average drops.

[ROB_GTR]

I can't confirm this but my daily work bus is a Mondeo 2.0TDCi and i am loosing approx 100 miles per tank over the past month or so.....

[Egg Chaser]

It happens to most modern cars. It's mostly because the colder air is denser, meaning more air enters the cylinders, so more fuel is injected to prevent the mixture being too lean.

[flakeypaul]

Egg Chaser said:

It happens to most modern cars. It's mostly because the colder air is denser, meaning more air enters the cylinders, so more fuel is injected to prevent the mixture being too lean.

I'm not sure that this is correct my friend - if you get more air into the cylinder, and inject more fuel, you get more power so you don't press the accelerator as hard, the throttle body doesn't open as far, less air gets in so less fuel is used.

I think it's got more to do with (in the case of diesels) additives being added to fuel to prevent freezing. Diesel freezes at about -7 (I'm sure someone will coreect me to something more accurate on this one) so has to be treated or everyone with a diesel would break down every time it got a bit cold! Also in bad weather we spend more time on the drive with the engine running while we clear the ice from the windows, we drive slower as there is less grip and you use more fuel as you are on the brakes more, etc etc.

My diesel has dropped from 39-42mpg round town to 32-34mpg.

[zakelwe]

I've noticed it more on my current diesel stebox than the petrol car. Lost 5mpg or so according to watching the display.

Andy

[fatboy b]

Need to factor in the additives they put in this time of year to stop the gelling. That knocks it a few mpg too.

WRT to the comment about about denser air, therefore more air gets in the cylinder. Utter rubbish with today's ecu controlled engines.

Edited by fatboy b on Friday 17th December 07:14

[Silverdaz]

You have also got to take in consideration that you will be warming the car up to defrost it for 5 mins before setting off, heated rear screen will be on, heater on more than usual, heated seats on (if have them) Maybe sat in traffic more due to the weather. My BM is now averaging 19mpg compared to around 23mpg in the warmer months.

[madbadger]

I'm getting slightly better economy.

I put it down to slower average speeds.

[kambites]

Have you checked your tyre pressures since it got cold?

On long trips it should make little difference, although as someone says above it will obviously run cold for longer when you first start it.

Edited by kambites on Friday 17th December 09:02

[jsg612]

Mine too is a little lower, but I put it down to warming the car up, sitting in traffic through snowy patches and general tick-over to keep warm in the cab whilst stationary.

[anonymous-user]

Cold air is more dense, so your cars aero drag increases significantly at low temps

[DannyVTS]

[redacted]

[RenesisEvo]

flakeypaul said:

I'm not sure that this is correct my friend - if you get more air into the cylinder, and inject more fuel, you get more power so you don't press the accelerator as hard, the throttle body doesn't open as far, less air gets in so less fuel is used.

Didn't think diesels had throttle bodies. AFAIK, the cylinder is filled with air, then more/less diesel is injected according to the load and throttle position. Hence diesels using very little fuel whilst idling.

Also remember in winter, you tend to have your lights and heating on, the energy to power these comes from your engine, hence you will see lower economy regardless of petrol or diesel.

Max_Torque said:

Cold air is more dense, so your cars aero drag increases significantly at low temps

This makes no contribution below 40mph, at which point tyre rolling resistance is the bigger contributor to drag. Plus, the overall change is going to be marginal at best.

Edited by RenesisEvo on Friday 17th December 13:07