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Fuel economy is worse in the morning that the evening
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NY
Sep 28, 2015, 5:34:46 AM9/28/15
to
I appreciate that the fuel economy of a car will be worse until the engine
has warmed up and the oil has started flowing freely.
But my wife has noticed that the average fuel economy figures reported by
our new car for the 40-mile journey to work in the morning are noticeably
worse (by up to 10 mpg) than for the same journey in reverse in the evening.
This is for a reasonably level route (it's not predominantly downhill one
way) and for similar traffic conditions (not constant 70 one way and
stop-start going the other way).
The car will have been standing overnight so in the morning the engine will
be starting from cold and with oil pooled in the sump, having last been
drive about 15 hours before, whereas in the evening it will last have been
driven about 8 hours before. Is that likely to make any difference? How long
after driving a car will the engine and oil cool down to a point that the
last-driven time becomes immaterial? Surely after 8 hours the engine will be
"cold". To what extent does ambient temperature matter? For example if it's
5 degrees in the morning after a clear night before the sun has started to
warm up the air, and then 20 degrees in the evening.
has warmed up and the oil has started flowing freely.
But my wife has noticed that the average fuel economy figures reported by
our new car for the 40-mile journey to work in the morning are noticeably
worse (by up to 10 mpg) than for the same journey in reverse in the evening.
This is for a reasonably level route (it's not predominantly downhill one
way) and for similar traffic conditions (not constant 70 one way and
stop-start going the other way).
The car will have been standing overnight so in the morning the engine will
be starting from cold and with oil pooled in the sump, having last been
drive about 15 hours before, whereas in the evening it will last have been
driven about 8 hours before. Is that likely to make any difference? How long
after driving a car will the engine and oil cool down to a point that the
last-driven time becomes immaterial? Surely after 8 hours the engine will be
"cold". To what extent does ambient temperature matter? For example if it's
5 degrees in the morning after a clear night before the sun has started to
warm up the air, and then 20 degrees in the evening.
AnthonyL
Sep 28, 2015, 7:42:14 AM9/28/15
to
i) the ambient temperature is higher
ii) the car has been used that day (coupled I think with i) )
iii) I don't vary from 50mph in 5th
iv) The engine is hot
My 2002 Focus mostly didn't care, hot/cold, slow/fast.
VW are not the only people that should come under the spotlight. I'm
wasting nearly 10% fuel thanks to the newer tuning. I can pay ~£350
to have it reprogrammed which the dealer wouldn't do whilst the car
was in warranty.
--
AnthonyL
Unknown
Sep 29, 2015, 6:10:01 AM9/29/15
to
On 28/09/2015 10:34, NY wrote:
> I appreciate that the fuel economy of a car will be worse until the engine
> has warmed up and the oil has started flowing freely.
>
> But my wife has noticed that the average fuel economy figures reported by
> our new car for the 40-mile journey to work in the morning are noticeably
> worse (by up to 10 mpg) than for the same journey in reverse in the
> evening.
> This is for a reasonably level route (it's not predominantly downhill one
> way) and for similar traffic conditions (not constant 70 one way and
> stop-start going the other way)...
> I appreciate that the fuel economy of a car will be worse until the engine
> has warmed up and the oil has started flowing freely.
>
> But my wife has noticed that the average fuel economy figures reported by
> our new car for the 40-mile journey to work in the morning are noticeably
> worse (by up to 10 mpg) than for the same journey in reverse in the
> evening.
> This is for a reasonably level route (it's not predominantly downhill one
> way) and for similar traffic conditions (not constant 70 one way and
Check the air temperatures. For various reasons, fuel economy is worse
when the air is colder.
--
Colin Bignell
spud-u-d...@potato.field
Oct 2, 2015, 7:59:01 AM10/2/15
to
have a slightly rougher surface compared to the other which can affect economy.
Though to be honest it is far more likely to be air temp + residual heat
in the engine. Remember an engine will cool down far quicker at night than
it will during the day especially if the sun is shining on the car.
--
Spud
NY
Oct 2, 2015, 8:31:32 AM10/2/15
to
<spud-u-d...@potato.field> wrote in message
news:8kuPx.33895$ii6....@fx15.am4...
Most engines seem to reach operating temperature (according to the
temperature gauge) within no more than 10 minutes, even in cold weather and
with a diesel engine.
I can believe the effect of colder air at the intake, though I'm still
trying to work out whether that would make economy better or worse, given
that some turbos have an intercooler to make the intake air cold and hence
more dense, so a given volume of intake air will contain more oxygen
molecules and hence be able to burn correspondingly more fuel (or, for a
petrol engine, maybe burn the same amount of fuel more efficiently).
news:8kuPx.33895$ii6....@fx15.am4...
temperature gauge) within no more than 10 minutes, even in cold weather and
with a diesel engine.
I can believe the effect of colder air at the intake, though I'm still
trying to work out whether that would make economy better or worse, given
that some turbos have an intercooler to make the intake air cold and hence
more dense, so a given volume of intake air will contain more oxygen
molecules and hence be able to burn correspondingly more fuel (or, for a
petrol engine, maybe burn the same amount of fuel more efficiently).
spud-u-d...@potato.field
Oct 2, 2015, 11:00:38 AM10/2/15
to
On Fri, 2 Oct 2015 13:31:36 +0100
"NY" <m...@privacy.net> wrote:
><spud-u-d...@potato.field> wrote in message
They're designed to give you peace of mind, not tell you the actual temp.
That aside an engine can use quite a surprising amount of fuel when its cold.
>I can believe the effect of colder air at the intake, though I'm still
>trying to work out whether that would make economy better or worse, given
>that some turbos have an intercooler to make the intake air cold and hence
>more dense, so a given volume of intake air will contain more oxygen
>molecules and hence be able to burn correspondingly more fuel (or, for a
>petrol engine, maybe burn the same amount of fuel more efficiently).
Wish I could respond, but its something you'll have to take up with a
mechanical engineer or petro chemist. I have no idea.
--
Spud
"NY" <m...@privacy.net> wrote:
><spud-u-d...@potato.field> wrote in message
>> A long shot, but also if shes driving on dual carraigeway, one side could
>> have a slightly rougher surface compared to the other which can affect
>> economy.
>> Though to be honest it is far more likely to be air temp + residual heat
>> in the engine. Remember an engine will cool down far quicker at night than
>> it will during the day especially if the sun is shining on the car.
>
>Most engines seem to reach operating temperature (according to the
>temperature gauge) within no more than 10 minutes, even in cold weather and
>with a diesel engine.
Don't believe what a temperature gauge tells you - they're not linear.
>> have a slightly rougher surface compared to the other which can affect
>> economy.
>> Though to be honest it is far more likely to be air temp + residual heat
>> in the engine. Remember an engine will cool down far quicker at night than
>> it will during the day especially if the sun is shining on the car.
>
>Most engines seem to reach operating temperature (according to the
>temperature gauge) within no more than 10 minutes, even in cold weather and
>with a diesel engine.
They're designed to give you peace of mind, not tell you the actual temp.
That aside an engine can use quite a surprising amount of fuel when its cold.
>I can believe the effect of colder air at the intake, though I'm still
>trying to work out whether that would make economy better or worse, given
>that some turbos have an intercooler to make the intake air cold and hence
>more dense, so a given volume of intake air will contain more oxygen
>molecules and hence be able to burn correspondingly more fuel (or, for a
>petrol engine, maybe burn the same amount of fuel more efficiently).
mechanical engineer or petro chemist. I have no idea.
--
Spud
Unknown
Oct 2, 2015, 2:22:51 PM10/2/15
to
> I can believe the effect of colder air at the intake, though I'm still
> trying to work out whether that would make economy better or worse,
> given that some turbos have an intercooler to make the intake air cold
> and hence more dense, so a given volume of intake air will contain more
> oxygen molecules and hence be able to burn correspondingly more fuel
> (or, for a petrol engine, maybe burn the same amount of fuel more
> efficiently).
tyre pressures, both of which increase fuel consumption. Colder tyres
are also less flexible, which increases the rolling resistance, while
lubricants are more viscous at lower temperatures. None of these has, by
itself, a huge effect, but they accumulate.
--
Colin Bignell
Recliner
Oct 2, 2015, 4:46:25 PM10/2/15
to
resistance? Of course, the lower tyre pressures in cold tyres would have
the opposite effect.
Nick Finnigan
Oct 8, 2015, 5:33:19 PM10/8/15
to
On 28/09/2015 10:34, NY wrote:
>
>
> The car will have been standing overnight so in the morning the engine will
> be starting from cold and with oil pooled in the sump, having last been
> drive about 15 hours before, whereas in the evening it will last have been
> driven about 8 hours before. Is that likely to make any difference? How long
> after driving a car will the engine and oil cool down to a point that the
> last-driven time becomes immaterial? Surely after 8 hours the engine will be
> "cold". To what extent does ambient temperature matter? For example if it's
> 5 degrees in the morning after a clear night before the sun has started to
> warm up the air, and then 20 degrees in the evening.
I've been driving a diesel this week, and it has taken 3 miles to warm up,
> be starting from cold and with oil pooled in the sump, having last been
> drive about 15 hours before, whereas in the evening it will last have been
> driven about 8 hours before. Is that likely to make any difference? How long
> after driving a car will the engine and oil cool down to a point that the
> last-driven time becomes immaterial? Surely after 8 hours the engine will be
> "cold". To what extent does ambient temperature matter? For example if it's
> 5 degrees in the morning after a clear night before the sun has started to
> warm up the air, and then 20 degrees in the evening.
morning or evening, wet or dry. It is 10 years old though, and does not
have an mpg readout. If your 40 miles could be split into 4 legs of about
10 miles, with a mpg for each, you might see where things are worse.
NY
Oct 9, 2015, 5:10:55 AM10/9/15
to
"Nick Finnigan" <N...@genie.co.uk> wrote in message
news:mv6ner$dmt$1...@speranza.aioe.org...
Good suggestion. If the economy was worst when the engine was cold, I'd
expect to see the trip average (automatically reset when the engine is
stopped and restarted) gradually increase (ie better mpg) as the journey
progresses.
My wife is very jealous that her CR-V gets about 45 at best and 35 on some
mainly-A-road journeys to work, whereas my Peugeot has always been about 55
and after having a new cat and diesel particulate filter (at "ouch"
prices!!! *) has miraculously started to report an average of around 60-70
mpg since the last filling - though I'll have to wait until the next
tank-filing to see if that's real or just a change in average that the trip
computer reports.
(*) It all started with a warning message "Risk of filter blocking" which
wasn't cured by driving in a low gear to race the engine and force the DPF
to regenerate. The Pug garage said it would need a new DPF (at 160,000
miles, so it's had a good life) to cure what was essentially a rogue
warning, because they couldn't see anything in the diagnostics to show that
the DPF was *really* getting blocked. So I was prepared for a £500 bill and
took the car in. And got a phone call a few hours later: it would need a new
cat as well because one of the nuts that secured a pipe into the cat had
jammed and would neither unscrew nor re-tighten :-( Another £500. Now you
see what I mean about "ouch prices". Still, the cat was probably due fir
replacement as well at 160,000.
news:mv6ner$dmt$1...@speranza.aioe.org...
expect to see the trip average (automatically reset when the engine is
stopped and restarted) gradually increase (ie better mpg) as the journey
progresses.
My wife is very jealous that her CR-V gets about 45 at best and 35 on some
mainly-A-road journeys to work, whereas my Peugeot has always been about 55
and after having a new cat and diesel particulate filter (at "ouch"
prices!!! *) has miraculously started to report an average of around 60-70
mpg since the last filling - though I'll have to wait until the next
tank-filing to see if that's real or just a change in average that the trip
computer reports.
(*) It all started with a warning message "Risk of filter blocking" which
wasn't cured by driving in a low gear to race the engine and force the DPF
to regenerate. The Pug garage said it would need a new DPF (at 160,000
miles, so it's had a good life) to cure what was essentially a rogue
warning, because they couldn't see anything in the diagnostics to show that
the DPF was *really* getting blocked. So I was prepared for a £500 bill and
took the car in. And got a phone call a few hours later: it would need a new
cat as well because one of the nuts that secured a pipe into the cat had
jammed and would neither unscrew nor re-tighten :-( Another £500. Now you
see what I mean about "ouch prices". Still, the cat was probably due fir
replacement as well at 160,000.
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