[LINK] Fuel consumption

[Darryl (Dassa) Lynch]

|> -----Original Message-----
|> From: link-bounces at mailman.anu.edu.au [mailto:link-
|> bounces at mailman.anu.edu.au] On Behalf Of Bernard Robertson-Dunn
|> Sent: Friday, May 27, 2011 10:14 AM
|> To: link at mailman.anu.edu.au
|> Subject: Re: [LINK] Fuel consumption
|> 
|> On 26/05/2011 8:48 PM, stephen at melbpc.org.au wrote:
|> > This is off-topic for Link, but, am wondering if the
|> physics/engineering
|> > (whatever) people here can suggest how to resolve something I've
|> been
|> > wondering, besides doing road tests.
|> >
|> > If a vehicle has an overdrive gear that kicks in at 80 klm/hour,
|> would it
|> > be better for fuel consumption to drive at 75 klm/h and higher revs,
|> or
|> > faster at 85 klm/h but with lower revs?
|> 
|> You don't say at what speed the overdrive gear drops out at. You could
|> try getting up to 80 k/hr, let it kick into overdrive and then slow
|> down
|> until just before the car changes up again.
|> 
|> BTW, there is another strategy that is quite useful. When coming up to
|> lights or a roundabout, change down and let the car drive the engine.
|> Fuel consumption drops to zero. That's because an idling engine
|> requires
|> fuel.  If you let the inertial of the car provide the energy, you
|> don't
|> use fuel for idling.
|> 
|> My car can show instantaneous fuel consumption. I've noticed that
|> changing from 5th to 4th makes no difference to the consumption, but
|> the
|> changing down strategy makes a significant difference. It also reduces
|> wear on the brakes.

I'd have to say that you do use fuel idling, while ever the engine is
running you are using fuel, you will use less fuel if you coast in either
neutral or with the engine off.

My car has an overdrive gear that kicks in at about 98 Km, if I run at 100 I
get far better fuel economy than if I run at 95. In the order of 3-4 Km/L.
When the overdrive kicks in the revs drop so I can travel the same distance
in a shorter time meaning the engine is running for less but at the same
revs or lower, hence saving fuel.

Darryl (Dassa) Lynch