Does anyone know the actual fuel consumption when an engine is at idle? Say
the very common 3.8 GM engine for instance.

Every gas saving tip articles says not to let your car warm up for long but
they never say how much you are burning.

Edwin Pawlowski wrote:
> Does anyone know the actual fuel consumption when an engine is at idle? Say
> the very common 3.8 GM engine for instance.
>
> Every gas saving tip articles says not to let your car warm up for long but
> they never say how much you are burning.
>
>

Not easy to measure BUT it would be burning a higher amount than when
you let it idle after it had warmed up. The computer looks at water temp
and air intake temps to calculate fuel delivery when in open loop (plus
a few other items) Due to both being colder the ECM adds fuel (just like
the old choke) to keep the engine running. The thinking is that by
driving while it is using that fuel you do two things. One the engine is
working harder so it warms up faster. Plus you are covering some
distance to your destination.

I can tell you that my 4.3 uses about 1 gallon while idling 2 hours.
That is idling with the heater on, 4 ways working and powering 600 watts
of light-bar. I leave it running when on calls to keep the lights on and
so I don't have to head back to the station in a cold rig.

--
Steve W.
Near Cooperstown, New York

Edwin Pawlowski wrote:
> Does anyone know the actual fuel consumption when an engine is at idle? Say
> the very common 3.8 GM engine for instance.
>
> Every gas saving tip articles says not to let your car warm up for long but
> they never say how much you are burning.
>
>
no matter how much or how little you actually burn, you are getting 0 MPG

"Steve W." <csr684NOT@yahoo.com> wrote in message
> I can tell you that my 4.3 uses about 1 gallon while idling 2 hours. That
> is idling with the heater on, 4 ways working and powering 600 watts of
> light-bar. I leave it running when on calls to keep the lights on and so I
> don't have to head back to the station in a cold rig.
>
> --
> Steve W.
> Near Cooperstown, New York

OK, lets call it an ounce a minute. At $3.58 a gallon, it works out to
..028 per minute. A 5 minute warm-up with a remote starter costs about 14¢ or
so.

Thanks, I was just curious what the price of comfort was.

"why, me" <kleingt-misc@yahoo.com> wrote in message
news:dQlMj.3422$vF.1531@newssvr21.news.prodigy.net ...
> Edwin Pawlowski wrote:
>> Does anyone know the actual fuel consumption when an engine is at idle?
>> Say the very common 3.8 GM engine for instance.
>>
>> Every gas saving tip articles says not to let your car warm up for long
>> but they never say how much you are burning.
> no matter how much or how little you actually burn, you are getting 0 MPG

Some people probably actually care too.

On Apr 12, 9:38*pm, "Edwin Pawlowski" <e...@snet.net> wrote:
> Does anyone know the actual fuel consumption when an engine is at idle? *Say
> the very common 3.8 GM engine for instance.
>
> Every gas saving tip articles says not to let your car warm up for long but
> they never say how much you are burning.

If my memory serves, our 3.1 Buick uses around .2GPH according to the
Scangauge.

I'll have to hook it up later today when I go out and get back to you
with the exact number.

The cost is much higher than that. His estimate was based on a warm engine
idling. A cold engine uses much more fuel than that, much of which washes
oil off of the cylinder walls and contaminates the motor oil, both
contributing to accelerated wear. An idling engine takes -much- longer to
warm up and remains in this destructive mode longer than one that is being
driven gently for the first few minutes.

Lee Richardson
Evansville, Indiana


> OK, lets call it an ounce a minute. At $3.58 a gallon, it works out to
> .028 per minute. A 5 minute warm-up with a remote starter costs about 14¢
> or so.
>
> Thanks, I was just curious what the price of comfort was.
>

"Lee Richardson" <mechtech@evansville.net> wrote in message
news:vZOdnYBZqPxZyZ_VnZ2dnUVZ_j2dnZ2d@sigecom.net. ..
> The cost is much higher than that. His estimate was based on a warm
> engine idling. A cold engine uses much more fuel than that, much of which
> washes oil off of the cylinder walls and contaminates the motor oil, both
> contributing to accelerated wear. An idling engine takes -much- longer
> to warm up and remains in this destructive mode longer than one that is
> being driven gently for the first few minutes.
>
> Lee Richardson
> Evansville, Indiana

Perhaps, we were taught that many years ago. I completely agree with older
engines, but I don't think newer ones have the same wear during warm-up as
the '57 Chevy with carburetor and choke coupled with wider tolerances of
rings. That engine also idled at a very high rpm compared to the computer
controlled injections systems we now have.

As for longer to warm up and stay in "destructive mode", that too is subject
to some analysis. If an engine idles at 800 rpm and sits for five minutes,
it has turned 4000 times in that period. Is there more wear than the car
being driven cold at 3000 rpm for two minutes? I don't know the answers to
that, but it makes some sense that total number of plug firings is going to
be a determinate of engine warm up to operating temperature.

Whether the air-fuel mixture is enriched on a cold start by using a
mechanical choke or by electronic fuel injection really makes no difference.
While there is no doubt the more modern system is capable of metering the
fuel more accurately, the fact remains a cold engine requires a -much-
richer mixture than a warm one. And an idling engine remains "cold" much
longer than one that is being driven. Anything that can be done to shorten
the length of time an engine runs cold will lengthen it's life and reduce
fuel cost. And even in that cold, fuel wasting state, the engine can still
be propelling the car down the road instead of sitting in the driveway.

Lee Richardson


> Perhaps, we were taught that many years ago. I completely agree with
> older engines, but I don't think newer ones have the same wear during
> warm-up as the '57 Chevy with carburetor and choke coupled with wider
> tolerances of rings. That engine also idled at a very high rpm compared
> to the computer controlled injections systems we now have.
>
> As for longer to warm up and stay in "destructive mode", that too is
> subject to some analysis. If an engine idles at 800 rpm and sits for five
> minutes, it has turned 4000 times in that period. Is there more wear than
> the car being driven cold at 3000 rpm for two minutes? I don't know the
> answers to that, but it makes some sense that total number of plug firings
> is going to be a determinate of engine warm up to operating temperature.
>

"Lee Richardson" <mechtech@evansville.net> wrote in message
news:wo6dnfprm8l2FZ_VnZ2dnUVZ_gCdnZ2d@sigecom.net. ..
> Whether the air-fuel mixture is enriched on a cold start by using a
> mechanical choke or by electronic fuel injection really makes no
> difference.

Again, in principle you are correct, but the electronic fuel measurment is
far superior than a thermostatic choke and light years ahead of a manual
choke. What I do not know, and evidently you don't either, is how much of a
difference there is. 5%? 50%? The old mechanical chokes stayed on until
you hit the gas pedal even if it was 20 minutes. Not so today. When cold,
my car runs about 150 - 200 rpm more than normal at starup and soon goes
down to normal, the old car was an additional 500+ rpm until I hit the gas
pedal or was driving and used the gas pedal.

> While there is no doubt the more modern system is capable of metering the
> fuel more accurately, the fact remains a cold engine requires a -much-
> richer mixture than a warm one.

But do we know how much? The idea of driving slowly goes back decades and I
think the practicality has changed. How rich is rich? What is the fuel air
ratio? What is the curve?


> And an idling engine remains "cold" much longer than one that is being
> driven. Anything that can be done to shorten the length of time an engine
> runs cold will lengthen it's life and reduce fuel cost. And even in that
> cold, fuel wasting state, the engine can still be propelling the car down
> the road instead of sitting in the driveway.

But you did not address my other idea. How does an engine get warmed up?
By burning fuel, or course, and it still takes a given number of cycles to
get from the cold start of say 0 degrees up to the water temperature of 210
and an even higher oil temperature. While driving shortens the clock time,
does it lessen the number of revolutions of the engine needed? If it needs
10,000 revolutions, does it matter if that takes place at 800 rpm over 13
minutes or 3000 rpm over 3.5 minutes? What is the fuel consumption either
way? I know you get 0 mpg while idling, but you've not presented real data
to the above questions. I doubt that many people know the real answer
outside of some engine design engineers or test lab guys.