Fuel (Lack of) economy - Winter's here! | Motoring discussion | Back Room Forum

Sat 1 Feb 2014 10:56

Fuel (Lack of) economy - Winter's here! - mss1tw

Fuel light came on well before the normal figure of 400 miles...according to FuelLog, the Berlingo did 33.6 mpg to the last tank!

The last fill up on the 18th worked out at 38.4mpg, looks like the winter diesel switchover has occured.

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Sat 1 Feb 2014 11:32

Fuel (Lack of) economy - Winter's here! - RT

The difference in energy content between summer diesel and winter diesel is very small - the reason for reduced economy is the cold weather which extends warm-up times and for many people the reduced amount of "leisure" trips.

The winter diesel supply period is from mid-October to mid-March - so the switch over was about 3 months ago!

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Sat 1 Feb 2014 11:49

Fuel (Lack of) economy - Winter's here! - mss1tw

The difference in energy content between summer diesel and winter diesel is very small - the reason for reduced economy is the cold weather which extends warm-up times and for many people the reduced amount of "leisure" trips.

The winter diesel supply period is from mid-October to mid-March - so the switch over was about 3 months ago!

Hmmm. I guess I should be grateful it's only recently economy has plummeted then!

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Sat 1 Feb 2014 13:21

Fuel (Lack of) economy - Winter's here! - Armitage Shanks {p}

SFAIK it is mainly a temperature related effect. With useage unchanged the fuel consumption in my 2 ltr Focus has dropped by 6 mpg since September.

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Sat 1 Feb 2014 13:35

Fuel (Lack of) economy - Winter's here! - Cyd

Have a look for other potential causes too. Check your air filter condition - round us there's a lot of building going on for example, so air filters are getting dirty quite quick. Also, is it due a service?

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Sat 1 Feb 2014 14:40

Fuel (Lack of) economy - Winter's here! - corax

'Winters here!'

Really?

Feels like Autumn to me.

If your car is returning worse economy now, imagine what it will be like when winter arrives.

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Sat 1 Feb 2014 15:06

Fuel (Lack of) economy - Winter's here! - Armitage Shanks {p}

It was about average temperature in January. Check out this chart.

www.gov.uk/government/statistical-data-sets/dukes-...s

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Sat 1 Feb 2014 15:47

Fuel (Lack of) economy - Winter's here! - Ordovices

Add to the winter diesel effect the fact that air at a 15 deg temperature drop will be around 5% denser, given the same car at the same speed then that could be a 5% fuel usage increase. The extra dense air would be a bonus if it were for a stationary generator or alike and would add to the efficiency, but not if you're shoving a box through it.

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Sat 1 Feb 2014 15:58

Fuel (Lack of) economy - Winter's here! - RT

On modern cars, diesel or petrol, variations in air density are detected by the sensors and the ECU causes more/less fuel to be injected AND less/more throttle to maintain the speed - the net result on fuel economy is zero.

Very different it was on carburetted cars, though.

Edited by RT on 01/02/2014 at 15:59

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Sat 1 Feb 2014 16:17

Fuel (Lack of) economy - Winter's here! - Armitage Shanks {p}

So how have I lost 6mpg when all that has changed is the winter mix petrol and the temperature?

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Sat 1 Feb 2014 16:25

Fuel (Lack of) economy - Winter's here! - RT

So how have I lost 6mpg when all that has changed is the winter mix petrol and the temperature?

The temperature - warm-up time is longer, requiring more energy to heat up the car and it's occupants.

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Sat 1 Feb 2014 17:13

Fuel (Lack of) economy - Winter's here! - Armitage Shanks {p}

Observed increase in fuel consuption, in cold weather, discussed here. The phenomenon does exist! green.autoblog.com/2009/11/12/greenlings-why-does-.../

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Sat 1 Feb 2014 17:22

Fuel (Lack of) economy - Winter's here! - RT

Is there a difference in US winter/summer gasoline, on which the article is based, and European winter/summer fuels - just asking ?

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Sat 1 Feb 2014 17:38

Fuel (Lack of) economy - Winter's here! - SteveLee

On modern cars, diesel or petrol, variations in air density are detected by the sensors and the ECU causes more/less fuel to be injected AND less/more throttle to maintain the speed - the net result on fuel economy is zero.

Very different it was on carburetted cars, though.

True if we all drive accelerating at exactly the same rate etc, most people drive robotically ie just plonk the accelerator down the same amount as usual etc - in which case cold dense air will cause you to burn more fuel, you will be accelerating quicker than usual but just won't notice. PS CV type carbs would also automatically compensate for air density just by the nature of the way they work.

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Sat 1 Feb 2014 20:21

Fuel (Lack of) economy - Winter's here! - focussed

Increased fuel consumption in cold weather is not solely due to any one thing, it's a combination of:-

Tyre pressures decrease in cold weather - higher rolling resistance.

The thermal mass of the engine and cooling system takes longer to warm up and

lube oil in engine and transmission takes longer to warm up-more drag for longer.

Diesel fuel reformulation in winter -more lighter fractions(kerosene) less dense, contains less energy, more needs to be injected to maintain the same power.

When driving at higher speeds for long periods the cold air that the car is pushing through is more dense so offers more resistance(drag) so needs more fuel to maintain speed.

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Sun 2 Feb 2014 00:35

Fuel (Lack of) economy - Winter's here! - unthrottled

PS CV type carbs would also automatically compensate for air density just by the nature of the way they work.

No, they don't. Venturis accurately meter volume flow, but they are oblivious to the density of said fluid.

Carbs should be more economical in winter because the mixture will be leaned out with denser air.

Regardless of the fuel delivery mechanism, denser air means more air resistance=worse economy.

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Sun 2 Feb 2014 16:07

Fuel (Lack of) economy - Winter's here! - SteveLee

No, they don't. Venturis accurately meter volume flow, but they are oblivious to the density of said fluid.

Carbs should be more economical in winter because the mixture will be leaned out with denser air.

Regardless of the fuel delivery mechanism, denser air means more air resistance=worse economy.

The needle or slide is raised based on the volume of air going through the carb and the pressure differential that provides - that's why CV type carbs are (to a point) self-calibraring for air density. Air density will affect volume.

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Sun 2 Feb 2014 12:16

Fuel (Lack of) economy - Winter's here! - Ordovices

You seem to have missed the point.

The air density affects the economy because the car has to push its way through more air, ie more molecules per unit volume. This will require more work to be done to maintain a comparable speed than in warmer, less dense, air. It's to do with drag rather than engine efficiency.

All other things being equal drag force is proportional to air density.

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Sun 2 Feb 2014 09:55

Fuel (Lack of) economy - Winter's here! - mss1tw

Have a look for other potential causes too. Check your air filter condition - round us there's a lot of building going on for example, so air filters are getting dirty quite quick. Also, is it due a service?

Nope oil is just less than 5000 miles old and the air filter is fine. It doesn't smoke excessively. Thanks though!

Edited by mss1tw on 02/02/2014 at 09:56

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Sun 2 Feb 2014 11:03

Fuel (Lack of) economy - Winter's here! - Armitage Shanks {p}

IMO cold starts, thicker oil and denser air are not going to fully explain a drop of mpg from 30 to 24.

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Sun 2 Feb 2014 13:37

Fuel (Lack of) economy - Winter's here! - madf

Cold starts are dramatic on fuel consumption. If you average 9say) 40mppg ariound town with a warm engine., expect 20mpg with a cold one - for at least a mile until it warms up. (If a diesel.. MUCH longer).

Based on observations of indicated mpg.

Add sticking handbrake initailly when starting due to rust (alloys/rain/rear disks)...acceleration when cold etc.. and a 20% increase in average fuel consumption is easily achievable. especially with an unsympathetic driver. Add heater, lights, demisting etc - especially with a cold engine - or leaving the car to warm up running - and it's easy to do worse.

I watch people leaving cars idling for 5 minutes outside their house on cold mornings.. Money to burn.

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Sun 2 Feb 2014 15:48

Fuel (Lack of) economy - Winter's here! - unthrottled

If you've ever tried pushing a cold car as opposed to a hot one,the difference is like night and day.

The wet mild winter is probably worse for economy than a cold dry one. The tires have to fight their way through water and the transmission stays cold.

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