Freewheeling, downsides?

Leyburn
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Joined: Fri May 25, 2012 5:15 pm

Freewheeling, downsides?

Postby Leyburn » Fri Jun 08, 2012 5:22 pm

Hi

Usual nanny message is don't freewheel because instant power isn't available if required for manoeuvring. But assume that driver skill can eliminate that risk.

My understanding is that older petrol cars with carburettors and no fuel cutoff on the overrun will use petrol when travelling in gear with foot off the accelerator (engine braking); with newer fuel injected cars the ECU senses no load on the engine when travelling in gear with foot off the accelerator and cuts the fuel supply. However, with freewheeling (coasting) some fuel is used to keep the engine idling. So does freewheeling save fuel? I've tried a couple of comparisons using the onboard fuel consumption indicator (instantaneous) on a couple of cars, can't see a difference over short distances, eg 1 mile.

Is there a definitive source of data to confirm that freewheeling saves fuel?

Also, some cars with manual gearboxes have a pump in the gearbox to maintain lubrication, any recorded issues of gearbox failure following extended freewheeling? Leyland LT77 springs to mind.

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frv
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Re: Freewheeling, downsides?

Postby frv » Sat Jun 09, 2012 11:25 am

I use more coasting in 'N' than I used to and my Ultra-Gauge has confirmed to me that this saves the most fuel most of the time. The steeper the hill the less benefit as less speed is lost through engine braking. It's a balance but freewheeling wins for me!
'15 Audi A3 Sportback SE CoD S-Tronic - 5+ year average 55+mpg
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(Retired) '06 Honda FR-V 2.2 i-CTDi - Best/longest tank: 67.92mpg (+51.6%) / 815.5 miles.

Leyburn
Posts: 5
Joined: Fri May 25, 2012 5:15 pm

Re: Freewheeling, downsides?

Postby Leyburn » Sun Jun 24, 2012 2:48 pm

Ok, thanks FRV.

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frv
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Re: Freewheeling, downsides?

Postby frv » Mon Jun 25, 2012 6:53 am

No problem - let us know how you get on...
'15 Audi A3 Sportback SE CoD S-Tronic - 5+ year average 55+mpg
Image

(Retired) '06 Honda FR-V 2.2 i-CTDi - Best/longest tank: 67.92mpg (+51.6%) / 815.5 miles.

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