Why use more petrol when its cold, than when its warmer?

[iCraig]

Can someone explain to me when its cold vehicles seem to be less efficient and get a lower MPG.

Yet when summer comes along MPG improves? Whats that all about? As I always thought fuel was denser when its colder?

Only reason why I ask is my car had being doing 31mpg on average all winter, and now its warmer its all of a sudden jumped up to 35mpg!
And I'm not driving it any different, well abit quicker if anything cos the roads are dry now?

Confused,

Craig

[Phil_G]

[Grav]

Air is less dense when it is warm and therefore can move more freely through your carb and filter system than cold air can. Also it mixes with fuel more efficiently and burns more evenly giving a better fuel economy.

Or summat like that.
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Dark Lord Of Custard

snigger.....

[R6jonny]

Colder air is denser, thus for a given volume you will have more oxygen, more oxygen requires/allows more fuel to be burnt hence you will use more in colder weather....

this is the premise behind free-er flowing air filters- they let in more air so more fuel gets burnt=more power!!

if that makes sense
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[iooi]

In the cold you have to use the choke to richen the mixture to aid starting and running till engine is upto a decent running temp. In warmer weather this is not needed.

Also remember in winter you are putting more load on the engine via the eletrics with heaters, fans and lights. More load = more fuel. Which is why air con knocks mpg down when used.
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Just because my bike was A DIVVY, does not mean i am......

[Dom_]

Would have thought this was an obvious one?!

Don't you own a turbo car, do you know what the intercooler does and why it does it?

[iCraig]

[Drew]

Have you not noticed your car is faster in the cold weather?

Cold air - dense air, more fuel required.

[5v3d3b0]

Always refuel in the cold - You get more for your money
And as said the fuel is denser in the cold so you essentially burn more.
But I love riding in the cold for that only reason, the bike feels like a beast.

[JonB]

I offset any MPG savings in the summer by pressing the "AC" button on me dash.
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[Dom_]

It's got nothing to do with how dense the fuel is Or what effect that does have will be very little.

If it's colder the air is more dense, more fits in the head, thus more fuel is put in. Thats exactly why you have an intercooler, to cool the air before it enters the engine.

[quacker_boy]