I have a 97 1.3 Fiesta with an endura engine. All through the summer I was getting 54 mpg. However now winter has come the consumption has fallen to 40 mpg. Is it usual for the winter consumption to fall so drastically The journeys are just the same, a 20 mile commute which is mainly rural driving. Any suggestions as to why the fuel consumption has fallen so much?

Possibly your tyre pressures? put a few tanks of premium petrol in as well, will help to clear the system of any muck that may have accumulated

The colder air of the winter is more dense which means there's actually more of it entering the air box.

A simple carburetta would add more fuel to stop the engine running lean. I should think a modern engine management system would compensate for air temp/pressure and control the amount of air entering the manifold. I'm not an expert. My old focus had an induction kit. I had to make a sock for it to wear over the winter.

As Marcr1 said check your tyre pressures, they might be down a bit. Remember fuel is also more dense and heavier so if you always have a full tank you will be lugging more weight around.

Alastair

Winter driving always takes a hit on MPG. Reasons I can think of are;

Colder engines are less efficient, thicker oil, petrol mixture running 'rich' for longer until engine warms up. Think this is the main culprit.

Engine running warming cabin whilst you scrap ice off windows.

All electrics running (heated screens, lights, blower etc) that are not used in summer adding extra load on engine

Weather wet and windy (although that sounds like this summer.....) causing more drag.

Tyre pressure drops a little increasing resistance.

I have a colleague with a BMW 320D who keeps detailed records of his MPG and it drops by a few mpg in winter. I mentioned that being a turbo intercooled Diesel the colder winter denser air should improve it abit but looks like the other things cancel it out.

Winter driving always takes a hit on MPG. Reasons I can think of are;

Colder engines are less efficient, thicker oil, petrol mixture running 'rich' for longer until engine warms up. Think this is the main culprit.

Engine running warming cabin whilst you scrap ice off windows.

All electrics running (heated screens, lights, blower etc) that are not used in summer adding extra load on engine

Weather wet and windy (although that sounds like this summer.....) causing more drag.

Tyre pressure drops a little increasing resistance.

I have a colleague with a BMW 320D who keeps detailed records of his MPG and it drops by a few mpg in winter. I mentioned that being a turbo intercooled Diesel the colder winter denser air should improve it abit but looks like the other things cancel it out.

+1 absolutely, you can add the lower calorific value of winter diesel to that list, re- diesels

if you spend 15 minites letting your car tick over as you scrape the windscreen etc, you could have driven 10 miles in that time (at a 40mph avarage) - this adds up if you do this all through the winter, and its not going to help the overall MPG

Agreed, although sometimes there is little difference between them, Summer and Winter have subtle differences that add up. To be honest, early 1800 summed it up quite nicely, temperature, thicker air, more air resistance, more drag, colder engine, and not all ECU's will compensate for the thicker air becuase it doesnt really detect it. If it does, it tends to overcompensate as well...

The colder season has dropped my mpg down by 2 mpg /: lol