Poor diesel mpg in winter
Discussion
Parrot of Doom said:
Why is diesel mpg generally lower, in cold weather like what we're experiencing now?
I usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
Are you sure about that? I'd have thought your style would have changed when faced with snow and ice, but if you've got the skills to deal with those conditions you adapt instinctively, so are not consciously 'trying' and so don't think you are. If that makes sense...I usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
You know I replaced 2 really manky air filters in Novemebr on my diesel where the dash had been telling me to sort it for 6 months and MPG dropped from a regular 40+ to 30-32mpg.Ive beem trying to suss it out ever since,...maybe its the temperature as you say.
Edited by andyc. on Tuesday 5th January 21:34
Dick_Phallus said:
Parrot of Doom said:
Why is diesel mpg generally lower, in cold weather like what we're experiencing now?
I usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
Are you sure about that? I'd have thought your style would have changed when faced with snow and ice, but if you've got the skills to deal with those conditions you adapt instinctively, so are not consciously 'trying' and so don't think you are. If that makes sense...I usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
My mpg in a petrol car is down too, and the main change in my driving over the last few weeks has been to slow right down. My 10 mile B road drive to work usually gives about 35mpg, 37mpg if I drive really slowly and about 15mpg on a de-stress drive home... At the moment I am getting about 32mpg whilst driving like Miss Daisy. I have put it down to running on choke for longer.
For those who are wondering, I don't get the calculator out after every journey, it just so happens that the on board computer thingy automatically displays the trip mpg.
For those who are wondering, I don't get the calculator out after every journey, it just so happens that the on board computer thingy automatically displays the trip mpg.
A few reasons really - And petrols are no different either...
1 ~ Cold air is more dense (meaning in effect more air in the cylinders), so more fuel can be burnt - Which means you get more power When you least want it
2 ~ As the ambient temperature is much lower, it takes much longer for the car to warm up, and as a result injector durations stay longer for longer (think - having teh choke on for longer in say, an old mini) - All assuming that is, that you drive a modern diesel with common rail injection (Which are mapped in much the same way as petrol engines now)
3 ~ Higher electrical loads - heater on longer, lights on morning and evening, heated rear screen etc) meaning the alternator has to work harder, creating a slightly higher load on the engine, which requires a sloght increase in fueling
Add in the fact that yu probably also leave the car running for 5 minutes or so in the morning whilst you defrost the windows, and Bingo, higher fuel consumption.
1 ~ Cold air is more dense (meaning in effect more air in the cylinders), so more fuel can be burnt - Which means you get more power When you least want it
2 ~ As the ambient temperature is much lower, it takes much longer for the car to warm up, and as a result injector durations stay longer for longer (think - having teh choke on for longer in say, an old mini) - All assuming that is, that you drive a modern diesel with common rail injection (Which are mapped in much the same way as petrol engines now)
3 ~ Higher electrical loads - heater on longer, lights on morning and evening, heated rear screen etc) meaning the alternator has to work harder, creating a slightly higher load on the engine, which requires a sloght increase in fueling
Add in the fact that yu probably also leave the car running for 5 minutes or so in the morning whilst you defrost the windows, and Bingo, higher fuel consumption.
Parrot of Doom said:
Why is diesel mpg generally lower, in cold weather like what we're experiencing now?
I usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
Winter diesel has a higher benzin content than summer diesel. The benzin reduces the tendancy for the fuel to wax at lower temperatures. The additional benzin content reduces the calorific value of the fuel, so for a given volume of fuel you will get less energy out of it - hence lower mpg for steady state driving conditionsI usually get about 450-500 miles per tank, for the last month or so I've been getting about 400-450. Driving style is completely unchanged.
wobert said:
Winter diesel has a higher benzin content than summer diesel. The benzin reduces the tendancy for the fuel to wax at lower temperatures. The additional benzin content reduces the calorific value of the fuel, so for a given volume of fuel you will get less energy out of it - hence lower mpg for steady state driving conditions
^ this - although it changes pretty early so it's not the whole story.Apart from the obvious cooler running and additional electrical loads, many diesel engines have a high power electrical heater embedded in the cooling system which assists warm up.
Deva Link said:
wobert said:
Winter diesel has a higher benzin content than summer diesel. The benzin reduces the tendancy for the fuel to wax at lower temperatures. The additional benzin content reduces the calorific value of the fuel, so for a given volume of fuel you will get less energy out of it - hence lower mpg for steady state driving conditions
^ this - although it changes pretty early so it's not the whole story.Apart from the obvious cooler running and additional electrical loads, many diesel engines have a high power electrical heater embedded in the cooling system which assists warm up.
It's only in recent years that "Winter Diesel" has been used in the UK, as it wasn't deemed to get cold enough here. From what I've heard, we now get WD from November through til the end of Feb
andy-xr said:
Idle is much higher on mine than normal recently, even when warm'ish. I guess the fuelling system is compensating for "other stuff"
My Kangoo snotter has also started this. Lumpy "chug chug" at the lights as normal then at the next set of lights a smooth "thrummmm" and 1k RPM ??????????????wobert said:
Deva Link said:
wobert said:
Winter diesel has a higher benzin content than summer diesel. The benzin reduces the tendancy for the fuel to wax at lower temperatures. The additional benzin content reduces the calorific value of the fuel, so for a given volume of fuel you will get less energy out of it - hence lower mpg for steady state driving conditions
^ this - although it changes pretty early so it's not the whole story.Apart from the obvious cooler running and additional electrical loads, many diesel engines have a high power electrical heater embedded in the cooling system which assists warm up.
It's only in recent years that "Winter Diesel" has been used in the UK, as it wasn't deemed to get cold enough here. From what I've heard, we now get WD from November through til the end of Feb
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