Why is mpg worse in winter

myhooose

It is a generally considered fact that mpg reduces in winter an I've noticed this myself. I've kept my tyre pressures up which is an obvious cause. so what causes it to drop?

In the microlight aeroplane I occasionally fly the opposite is true. Some of this is due to the denser cold air generating more lift and giving more 'bite' on the propeller, however the engine itself seems to like the colder air.

Any suggestions?

Strider590

Because your using lights/wipers/heater in the winter AND the engine take much longer to get up to normal (most efficient) operating temperature.

Plus using your heating cools the engine because your ramming cold air through the small heating radiator inside the car as well as the big one under the bonnet.

Then there are secondary reasons like increased traffic due to 90% of the population forgetting how to drive in the winter.


A car does like cold air intake (once fully warmed up), your theory is correct regarding air density, but this is mostly outweighed by the other negative effects.

If your doing short mileage, you'll be lucky to see 3/4 of your regular MPG.

forgotmyname

I agree with the above post, You might be surprised at how much power it takes to turn an alternator.

I tried running one off an electric drill, Drill was 400 or 600 watts. Had a belt running from the drill to the alternator,
As soon as i added a load which was one 55W headlamp bulb the alternator stopped dead. The drill couldnt turn it.

So as mentioned with the lights, wipers and heater on your putting quite a load on the engine.

Lots of people dont like driving in the dark so drive slower.

thescouselander

The biggest thing is the cold start. When the engine is cold it needs to run a slightly richer fuel mixture and the colder temperatures of winter means the richer mixture is run for longer as the engine takes loger to reach running temperature. This really shows when you're only doing short journeys.

Weird_Nev

They change the fuel mix to a "winter mix" too - particularly in diesels to stop it waxing in the cold. This mix is less calorific and so returns worse Mpg.

harveybobbles

Biggest killer is stuff like heated rear windows and heated seats.

petrolhead69

as well as the above engine and gearbox oil are noticably thicker, bearings etc are tighter when cold. its noticably harder to push or bump start a car in cold weather as it is in hot weather.

[Deleted User]

I've just got 340 miles out of a 50 litre tank from brim to empty. Last time I brimmed the tank in the summer I got nearer 400 miles. But it could just be my driving.

Wig

And you need to watch out you are not running with an open thermostat, that will increase fuel big time in winter.

Your top hose should remain cold until suddenly the gate opens and it gets hot, the temp gauge should rise and rise and rise and then suddenly fall when the thermostat opens, at this time the top hose wil be suddenly hot.

LandyAndy

forgotmyname wrote: »

I agree with the above post, You might be surprised at how much power it takes to turn an alternator.

I tried running one off an electric drill, Drill was 400 or 600 watts. Had a belt running from the drill to the alternator,
As soon as i added a load which was one 55W headlamp bulb the alternator stopped dead. The drill couldnt turn it.

So as mentioned with the lights, wipers and heater on your putting quite a load on the engine.

Lots of people dont like driving in the dark so drive slower.

I don't doubt you did it:).

Why?

vikingaero

LandyAndy wrote: »

I don't doubt you did it:).

Why?

A bit like scratching our balls - it feels nice and we can.

As others have mentioned: cold starts, use of lights/heaters/rear window demist, changes in fuels. But also if it's raining you'll generally get a lower mpg due to the increased drag from the water on the road (there is a fine line between the presence of water which will decrease your rolling resistance and improve your mpg and that of rain which will harm your mpg).