Fuel efficient driving.

cyclonebri1

skiddlydiddly wrote: »

Yes I am getting coasting and free-wheeling mixed up.Interesting how rolling down a hill in neutral uses more fuel than being in gear when you'd maybe expect the drag of the gearbox to increase fuel used.

Well does it? There's arguments both ways that all make some sense.

It should be possible to prove given some sparetime, (and petrol:eek:), and a car with instantaneous fuel consumption read out, a stop watch, an empty downhil road etc etc. So quite difficult

almillar

Coasting and freewheeling is the same thing. It's rolling along without a gear engaged (ie in neutral or with the clutch pedal pressed). Idling petrol used.
You need to separate this from simply taking your foot off the accelerator whilst in gear. This cuts the fuel in most injected cars, but is 'stalling' the car and the engine stays alive through the movement from the wheels connecting it through the gearbox. This running of the engine causes drag and makes the car slow down. This can be useful for holding the car back when going down a hill instead of the car running away with you, or melting the brakes!
So when deciding what is more fuel efficient, you need to decide 'how quickly do I need to slow down?'. If you're approaching red lights - are you going to stop? Keep it in gear. Are you going to make it through? Let it roll, planning to accelerate again just as the lights change when you approach the junction.
Judging these situations well is very good driving, can save big stops and starts (or at least slow-downs and speed-ups) and save loads of time and fuel, and wear!

skiddlydiddly

Obviously I was referring to free wheeling in neutral.I know all about the rest of your post though thanks .

Harry_Flashman

I came home over the pennines this evening and managed 2.3 miles downhill out of gear - the motor (and it's a big heavy one) just about maintained speed all the way. In gear without the accelerator I'd never have achieved that - it must be cheaper to freewheel in these circumstances.

John_3:16

Sorry not had time to read all the posts, I will do latere.

I have found that keeping my car clean (washed) and polished helped mpg. It seems a slippy car cuts the air alot better.

A small amount of time to also help.

cyclonebri1

Harry_Flashman wrote: »

I came home over the pennines this evening and managed 2.3 miles downhill out of gear - the motor (and it's a big heavy one) just about maintained speed all the way. In gear without the accelerator I'd never have achieved that - it must be cheaper to freewheel in these circumstances.

But as I said it's going to take some proving.

Go on then spanner in the works time.

Out of gear with engine running or not??:A. I know I know, no power assited brakes, no abs, no pas, no speedo and not to mention the possiblity of putting the steering on lock.

I bet someone on here has tried it by turning the ignition of and quickly turning it back on but without starting the engine.
The ultimate in economy and stupidity in one move;);)

standard disclaimer;
please don't try this at home (try it on the road instead)

Harry_Flashman

No matey - out of gear but with the engine running. The brakes and steering are both power assisted so that would be daft.

artybee

Would it also be true to say that accelerating whilst going up hill is wasteful?

jeferey

artybee wrote: »

Would it also be true to say that accelerating whilst going up hill is wasteful?

Yes. Better to increase speed through gravity going downhill (and maybe a bit of throttle if required) and 'bleed' your speed going up the hill on the other side.

cyclonebri1

Harry_Flashman wrote: »

No matey - out of gear but with the engine running. The brakes and steering are both power assisted so that would be daft.

Actually Harry it was very tongue in cheek.;)

Since the earlier posts I've played around with this a little and regardless of the "correctness" of coasting out of gear, I'm now convinced that it does give the max fuel return. Trying both methods on a daily undulating road, for the same fuel usage I can get both further and travel more quickly by coasting rather than in gear/foot off driving.