hello everyone and welcome how much fuel
do you think it takes to start up an
engine another way of asking this
question how much time does it take an
idling engine to use the same amount of
fuel required to start up an engine now
if you knew the answer to this question
you could potentially save fuel if you
knew how long you were going to be
sitting in a stoplight or something like
that perhaps a train is crossing by and
you could also answer whether or not
start stop systems in modern cars are
actually doing anything now according to
a study published in the journal of
energy policy they asked 1300 u.s
drivers how long they thought it would
take before it was more beneficial to
shut an engine off rather than let it
idle and the average response amongst
1300 participants in that study was 3.6
minutes the good news is we don't have
to guess or ask our uncle or cousin or
whoever about how much fuel an engine
uses while it's idling it's well
researched the data is out there you
just have to go and read it and so this
is how much fuel a small four-cylinder
engine will consume while idling for 3.6
minutes and this is how much fuel it
actually takes to start that same engine
up small four-cylinder engine so this is
what the average american thinks it
takes to start up a four-cylinder engine
and this is how much fuel it actually
takes to start up a small four-cylinder
engine now if you're embarrassed because
you're an american and you had no clue
how much it takes to start up an engine
don't worry i'm sure plenty of the rest
of the world also didn't know how much
fuel it takes to start up an engine i
mean i didn't know
wait i'm american
so no more guessing in 2004 a study
published in the journal of sae sought
to find out whether or not engine start
stop systems actually improve fuel
economy the study took two identical
cars both with 1.5 liter four-cylinder
toyota gasoline engines and they
equipped them with fuel flow meters so
they could measure the fuel going into
the engine being consumed now to get a
baseline measurement of the engine's
idling fuel consumption they idled both
vehicles in both park and then in drive
for 90 minutes and measured how much
fuel they used during those 90 minutes
you then do a little bit of division and
you come down to the fuel flow rates for
an idling engine so this is how much
fuel an idling 1.5 liter engine uses in
just 10 minutes so if you had six of
these that would tell you how much it
uses in an hour so it's about .63 liters
or about one sixth of a gallon that this
idling engine will use every hour and of
course if the displacement of that
engine is larger then it's going to use
even more than this it's also
interesting to note that there really
wasn't much of a difference between
having the car in park and having the
car in drive as far as how much fuel it
was consuming while idling so next they
wanted to find out how much fuel does it
take to start up an engine and so in
order to do this they started and
stopped the engine a ton of times
basically what they did is they did they
started they stopped it they started
they stopped it until it had used the
same amount of fuel that the engine had
used while spending 90 minutes idling
from there it's a pretty simple equation
you take the total amount of fuel used
and you divide it by the number of times
that you started the car and that's
where they came up with the 1.1 to about
1.2 milliliters of fuel required in
order to start a 1.5 liter engine okay
you're still following right so if you
take the amount of fuel required to
start up the engine and you divide it by
how much fuel the engine uses while
idling in fuel per second then you get
how many seconds does this engine have
to idle in order for it to be more
beneficial to instead simply shut it off
so if you take 1.2 and you divide it by
0.171
cc per second which is the fuel rate at
idle then you get about seven seconds so
if this engine is idling or a 1.5 liter
four-cylinder engine is idling for seven
seconds if it's going to idle for any
longer it's more beneficial to simply
shut it off and then restart it once
traffic is moving again now i'm sure
this is where plenty of your heads start
exploding you say jason it's not safe to
turn your car off in traffic or i need
my ac look i'm not telling you how to
live your life or drive i don't really
care what you do what i'm telling you is
just the data behind fuel consumption so
if you want to save fuel if that was
your only goal how you drive is your
business do whatever you want to do but
just letting you know after you let that
engine idle for longer than about seven
seconds your wasting fuel had you just
let it shut off so that's the
justification for a lot of the systems
out there which do have start stop which
by the way they have completely
different starters which are used to
start those up so they're built for many
more repetitions many more starts and
stops they're designed for it from the
start it turns out engineers are capable
of thinking about these things knowing
that hey if you use a starter a ton of
times you probably need to design for it
they do it don't worry about it so if
you do want to save fuel using a start
stop system what this is showing is that
if your car is shut off for longer than
seven seconds then it could be
beneficial wait come back i see that
mine wandering on me again now you're
thinking jason but this isn't a 1.5
liter engine so surely in a larger
engine you know maybe that doesn't it
maybe it's longer than seven seconds
well you know that could be but here's
the thing the larger engine is not only
going to require more fuel to start up
it's also going to require more fuel to
idle so the ratio may remain somewhat
similar so estimating about seven
seconds eight seconds nine seconds isn't
that crazy to do because as the engine
gets larger it takes more fuel to start
up it takes more fuel for it to idle
okay now we get to the final part of the
study and this is really cool so what
they wanted to find out was whether or
not engine start stop systems actually
save any fuel and so what they did is
they took both vehicles they equipped
one of them with a start stop system and
then they had the other always running
when it came to a stop so the engine
would idle at a stop versus the other
one would shut off whenever it came to a
stop so they took both of these vehicles
and they drove the same route in four
different ways so four different types
of traffic so it was you know real world
driving uh just using real traffic and
they just put one car right behind the
other and this is city driving so we
don't have to worry about aerodynamics
playing a role here the front car you
know towing the car behind it uh the the
speeds are very low so real world city
driving test to show you know does this
actually save you any fuel uh you know
when of course start stop systems are
designed to save you fuel in-city
driving and so the cars are right behind
each other they're driving the exact
same route and the exact same traffic
and they range from light traffic to
heavy traffic and what they found is
that in all four of those scenarios the
car with start stop actually got the
best fuel economy and so it ranged from
about four percent better to as high as
8.7 better fuel economy with the car
that did have start stop equipped okay
so what have we learned well first of
all it takes very little fuel in order
to actually start up your car just about
1.2 milliliters to start up a 1.5 liter
four-cylinder engine especially when
comparing that to how much fuel an
engine uses while idling we also learned
that if your engine is idling for longer
than about seven seconds you're actually
starting to waste fuel and finally real
world city driving shows that you can
actually save about four to eight point
seven percent in fuel economy by using a
start stop system versus just letting
the engine idle when you come to a stop
now of course feel free to let me know
in the comments below why everything
about this video is nonsense thank you
all so much for watching