2005 Honda Civic LX gas mileage

Elle wrote:
> Your mileage should decline as the weather cools. In a nutshell, the
> engine requires more fuel to achieve the same speeds etc. at lower
> temperatures.

> In July and August, for seven fillups, the mpg varied from 40 mpg to
> 45 mpg (45, 44, 41, 40, 45, 40, 41). I almost always put in over 8
> gallons but rarely lately over 10 gallons. It does seem that I get
> better mileage if I don't drive as near to an empty tank as possible.
> (The fuel pump doesn't have to work as hard, reducing energy consumed
> to run it? That may be out in left field.)

The load on the fuel pump is virtually constant. It delivers fuel at
pressure
to the engine compartment where it is filtered and applied to the injector
pump while the volume not required is returned to the tank.


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

"Graham W" > wrote
> Elle wrote:
> > Your mileage should decline as the weather cools. In a nutshell, the
> > engine requires more fuel to achieve the same speeds etc. at lower
> > temperatures.
>
> > In July and August, for seven fillups, the mpg varied from 40 mpg to
> > 45 mpg (45, 44, 41, 40, 45, 40, 41). I almost always put in over 8
> > gallons but rarely lately over 10 gallons. It does seem that I get
> > better mileage if I don't drive as near to an empty tank as possible.
> > (The fuel pump doesn't have to work as hard, reducing energy consumed
> > to run it? That may be out in left field.)
>
> The load on the fuel pump is virtually constant.

The difference in pressure across a pump, among other things like flow rate
and fluid density, is what determines the pump load.

A higher head at the pump inlet reduces the amount of work it must do.

Higher levels in the fuel tank translate of course to a higher head at pump
inlet.

Thus my proposal. Admittedly the difference may be negligible. The theory,
with practical consequences in many applications and being a routine part of
pump design, is correct.

My '05 Civic LX coupe with automatic transmission delivers between 23 and
25 mpg in-town driving. Freeway driving will produce low 30's; so I'd say
you're doing good 32 mpg.


cinerama wrote:

> When I picked up my Honda Civic LX that I just bought on 9/7/2005, it
> had a full tank of gas. I drove it over 400 miles, did a fill up,
> divided the gallons into the miles and it came out to 39 mpg. I thought
> this was great, since I had the AC on at various times, did more city
> driving than I normally do, etc. But, with my next fill up, less AC and
> less city driving it came out to only 37 mpg. Then 36 mpg with the next
> fill up. It keeps going down. The last fill up it was 32 mpg. I don't
> do fast start ups or slowing down and I drive the car at 60-65 mph on
> the highway with no AC. I now have 3,200 miles on it. I called the
> Honda dealer and asked them if they could check it out to see what the
> problem is. To my surprise, they said that the better gas mileage I was
> getting before was a fluke! What I am getting now is normal. They said
> there was nothing for them to check unless I start getting around 19
> MPG or the service engine light comes on. They said the engine is run
> by computers so there is nothing for them to do. Is this right?
>
> Thanks,
>
> Roland

--
Tp,

-------- __o
----- -\<. -------- __o
--- ( )/ ( ) ---- -\<.
-------------------- ( )/ ( )
-----------------------------------------

No Lawsuit Ever Fixed A Moron...

Elle wrote:
> "Graham W" > wrote
>> Elle wrote:
>>> Your mileage should decline as the weather cools. In a nutshell, the
>>> engine requires more fuel to achieve the same speeds etc. at lower
>>> temperatures.
>>
>>> In July and August, for seven fillups, the mpg varied from 40 mpg to
>>> 45 mpg (45, 44, 41, 40, 45, 40, 41). I almost always put in over 8
>>> gallons but rarely lately over 10 gallons. It does seem that I get
>>> better mileage if I don't drive as near to an empty tank as
>>> possible. (The fuel pump doesn't have to work as hard, reducing
>>> energy consumed to run it? That may be out in left field.)
>>
>> The load on the fuel pump is virtually constant.
>
> The difference in pressure across a pump, among other things like
> flow rate and fluid density, is what determines the pump load.
>
> A higher head at the pump inlet reduces the amount of work it must do.
>
> Higher levels in the fuel tank translate of course to a higher head
> at pump inlet.
>
> Thus my proposal. Admittedly the difference may be negligible. The
> theory, with practical consequences in many applications and being a
> routine part of pump design, is correct.

I did say "virtually constant" and you missed a significant factor
(for in-tank pumps in the Honda/Rover cars) which is that the fuel is
sucked into the pump without being replaced by air from the outside
thus reducing the absolute air pressure in the tank. You can verify this
by listening for the 'whoosh' of air into the tank when you undo the
tank's filler cap.

From time to time, the depression is great enough to activate the
ingress of air through the filtered vent used as part of the emission
controls. This causes a strange sort of 'groan' from the valve when
the car is stationary and engine is off.

Since the head at the inlet varies by only a few inches, I doubt that
the difference in electrical load is measurable.


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

"Graham W" > wrote
> Elle wrote:
> > "Graham W" > wrote
> >> Elle wrote:
> >>> Your mileage should decline as the weather cools. In a nutshell, the
> >>> engine requires more fuel to achieve the same speeds etc. at lower
> >>> temperatures.
> >>
> >>> In July and August, for seven fillups, the mpg varied from 40 mpg to
> >>> 45 mpg (45, 44, 41, 40, 45, 40, 41). I almost always put in over 8
> >>> gallons but rarely lately over 10 gallons. It does seem that I get
> >>> better mileage if I don't drive as near to an empty tank as
> >>> possible. (The fuel pump doesn't have to work as hard, reducing
> >>> energy consumed to run it? That may be out in left field.)
> >>
> >> The load on the fuel pump is virtually constant.
> >
> > The difference in pressure across a pump, among other things like
> > flow rate and fluid density, is what determines the pump load.
> >
> > A higher head at the pump inlet reduces the amount of work it must do.
> >
> > Higher levels in the fuel tank translate of course to a higher head
> > at pump inlet.
> >
> > Thus my proposal. Admittedly the difference may be negligible. The
> > theory, with practical consequences in many applications and being a
> > routine part of pump design, is correct.
>
> I did say "virtually constant" and you missed a significant factor

Now it's "significant" huh.

> (for in-tank pumps in the Honda/Rover cars) which is that the fuel is
> sucked into the pump without being replaced by air from the outside
> thus reducing the absolute air pressure in the tank.

> You can verify this
> by listening for the 'whoosh' of air into the tank when you undo the
> tank's filler cap.
>
> From time to time, the depression is great enough to activate the
> ingress of air through the filtered vent used as part of the emission
> controls.

Contradicting your earlier statement.

> This causes a strange sort of 'groan' from the valve when
> the car is stationary and engine is off.
>
> Since the head at the inlet varies by only a few inches, I doubt that
> the difference in electrical load is measurable.

I haven't run numbers but I do /not/ maintain it's significant. I don't
know. I raised it only as a possibility above. The possibility is in fact
consistent with theory.

Now I'm outta this exchange because I know a pig when I read one.

You know what I'm talking about.

Others who have read my posts he Graham is the one. Open emails from him
with caution.

Elle wrote:

> Now I'm outta this exchange because I know a pig when I read one.
>
> You know what I'm talking about.
>
> Others who have read my posts he Graham is the one. Open emails
> from him with caution.

I have never ever emailed a person at your e-address. Please show
the headers of where I did or apologise for making false allegations!

I do not give other correspondants Trojans or Viruses or any other
nasties.


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

> I did say "virtually constant" and you missed a significant factor
> (for in-tank pumps in the Honda/Rover cars) which is that the fuel is
> sucked into the pump without being replaced by air from the outside
> thus reducing the absolute air pressure in the tank. You can verify this
> by listening for the 'whoosh' of air into the tank when you undo the
> tank's filler cap.

One should note here that, as long as the tank is not vented to atmosphere,
then the pressure due to the air above the fuel level in fact will be
reducing (contrary to the implication above) as long as the fuel level goes
down. Thus the pressure at the pump inlet will be even lower than if the
tank were vented to atmosphere.

With no venting, even more pump work is necessary than with venting.

It's mere theory, and in this application out in left field, because the
pump is such a low power device, raising say 1 gallon / hour a few psi, well
less than 1 hp of motor power, I'd guesstimate with some rough calculations.

Elle wrote:
>> I did say "virtually constant" and you missed a significant factor
>> (for in-tank pumps in the Honda/Rover cars) which is that the fuel is
>> sucked into the pump without being replaced by air from the outside
>> thus reducing the absolute air pressure in the tank. You can verify
>> this by listening for the 'whoosh' of air into the tank when you
>> undo the tank's filler cap.
>
> One should note here that, as long as the tank is not vented to
> atmosphere, then the pressure due to the air above the fuel level in
> fact will be reducing (contrary to the implication above)

It isn't contrary - that is exactly what I said - "reducing the absolute
pressure in the tank"!

> as long as
> the fuel level goes down. Thus the pressure at the pump inlet will
> be even lower than if the tank were vented to atmosphere.

Agreed.

> With no venting, even more pump work is necessary than with venting.

Agreed again.

> It's mere theory, and in this application out in left field, because
> the pump is such a low power device, raising say 1 gallon / hour a
> few psi, well less than 1 hp of motor power, I'd guesstimate with
> some rough calculations.

Your figures are a bit adrift though. Yes I know they are guesses but
since the pump needs to raise the delivery pressure at the filter so
that the engine's FI is supplied with enough fuel at the most extreme
of power demands and RPM, the volume at a guess is far higher than
1 gallon / hour. That fuel which isn't consumed by the FI injectors is
returned to the tank through a pressure relief valve. So at 90 mph
the engine will be burning around 3 gal / hr or more and that figure
doesn't include the amount returned to the tank.

Here are some figures to play with. The pump output pressure runs
at 2.3 to 3.0 bar (that's about 33 to 44 psi). At 16volts it can deliver
at nearly 60 psi. Figures taken from Haynes for my Honda engined
Rover 216 16 valve 1.6 litre.

How do those numbers run out at HP needed from the pump?


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

"Graham W" > wrote
> Elle wrote:
> >> I did say "virtually constant" and you missed a significant factor
> >> (for in-tank pumps in the Honda/Rover cars) which is that the fuel is
> >> sucked into the pump without being replaced by air from the outside
> >> thus reducing the absolute air pressure in the tank. You can verify
> >> this by listening for the 'whoosh' of air into the tank when you
> >> undo the tank's filler cap.
> >
> > One should note here that, as long as the tank is not vented to
> > atmosphere, then the pressure due to the air above the fuel level in
> > fact will be reducing (contrary to the implication above)
>
> It isn't contrary - that is exactly what I said - "reducing the absolute
> pressure in the tank"!

You seemed to be implying this reduced the pump work. On the contrary, lower
pressure on the fuel in the tank increases the pump work necessary to move
it to the injectors, etc.

That junk you posted did nothing more than bolster my original point, but in
a manner that muddies the issue.

> > as long as
> > the fuel level goes down. Thus the pressure at the pump inlet will
> > be even lower than if the tank were vented to atmosphere.
>
> Agreed.
>
> > With no venting, even more pump work is necessary than with venting.
>
> Agreed again.
>
> > It's mere theory, and in this application out in left field, because
> > the pump is such a low power device, raising say 1 gallon / hour a
> > few psi, well less than 1 hp of motor power, I'd guesstimate with
> > some rough calculations.
>
> Your figures are a bit adrift though. Yes I know they are guesses but
> since the pump needs to raise the delivery pressure at the filter so
> that the engine's FI is supplied with enough fuel at the most extreme
> of power demands and RPM, the volume at a guess is far higher than
> 1 gallon / hour.

Whatever "at a guess" means.

Of course the flow varies. Why would you suggest otherwise, except to be a
jackass?

I don't work with absurd numbers such as 90 mph, but instead numbers for the
typical driver in the U.S.

You're not greeted with seriousness or patience by me, because of that
vulgar email you sent.

Elle wrote:
> "Graham W" > wrote
>> Elle wrote:
>>>> I did say "virtually constant" and you missed a significant factor
>>>> (for in-tank pumps in the Honda/Rover cars) which is that the fuel
>>>> is sucked into the pump without being replaced by air from the
>>>> outside thus reducing the absolute air pressure in the tank. You
>>>> can verify this by listening for the 'whoosh' of air into the tank
>>>> when you undo the tank's filler cap.
>>>
>>> One should note here that, as long as the tank is not vented to
>>> atmosphere, then the pressure due to the air above the fuel level in
>>> fact will be reducing (contrary to the implication above)
>>
>> It isn't contrary - that is exactly what I said - "reducing the
>> absolute pressure in the tank"!
>
> You seemed to be implying this reduced the pump work.

But I didn't say that.

> On the
> contrary, lower pressure on the fuel in the tank increases the pump
> work necessary to move it to the injectors, etc.

Agreed.

> That junk you posted did nothing more than bolster my original point,
> but in a manner that muddies the issue.
>
>>> as long as
>>> the fuel level goes down. Thus the pressure at the pump inlet will
>>> be even lower than if the tank were vented to atmosphere.
>>
>> Agreed.
>>
>>> With no venting, even more pump work is necessary than with venting.
>>
>> Agreed again.
>>
>>> It's mere theory, and in this application out in left field, because
>>> the pump is such a low power device, raising say 1 gallon / hour a
>>> few psi, well less than 1 hp of motor power, I'd guesstimate with
>>> some rough calculations.
>>
>> Your figures are a bit adrift though. Yes I know they are guesses but
>> since the pump needs to raise the delivery pressure at the filter so
>> that the engine's FI is supplied with enough fuel at the most extreme
>> of power demands and RPM, the volume at a guess is far higher than
>> 1 gallon / hour.
>
> Whatever "at a guess" means.

The same as your guess.

> Of course the flow varies. Why would you suggest otherwise, except to
> be a jackass?

Ah, but the flow remains essentially constant. This is fact that you
have failed to grasp. Any fuel at say 2.5 bar which is not consumed by
the FI is returned to the tank.

> I don't work with absurd numbers such as 90 mph, but instead numbers
> for the typical driver in the U.S.

> You're not greeted with seriousness or patience by me, because of that
> vulgar email you sent.

Show me the headers! In fact show me the email.

And read more carefully what I have posted - you are trying to twist
what I say to suit yourself.


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro-society.freeserve.co.uk/ Wessex
Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.