driving in neutral to save fuel

computershack

kaya wrote: »

qualified electrical and mechanical engineer,

So none as a vehicle mechanic then. Thankyou for confirming my suspicions.

almillar

OP's friend thinks too much for an automatic driver. Auto drivers should just be sticking it in D and leaving it there. If you want more control, get a manual.
The opinions stated here are quite correct, officially (apart from the 'it's illegal' one!). You do lose a lot of control by not being in gear and having the drivetrain all connected up. And most fuel injected cars do cut off the fuel supply when slowing down in gear.
I think that with experience, coasting is fine. If I need to slow down, I stay in gear - this means my brakes don't need to work as hard and also means no fuel burnt. If I don't want to slow down too much I'll coast - for example when I can see that I'm coming up to a queue of slow moving traffic, in urban conditions, I'll coast. I'm only using idling fuel, will get to the back of the queue and match their speed, and back into gear.
Anyone who tells me I'm not in control of my vehicle in this situation is a pedant!

GSXRCarlos

almillar wrote: »

Anyone who tells me I'm not in control of my vehicle in this situation is a pedant!

Like always there's a time and a place, as long as you are aware of your surroundings i see no problem with this attitude :j

Wig

Recently driving a punto with a fuel use display, I experimented
Driving in gear with supposed overrun able to kick in if it it exists on the vehicle
fuel display eventually reached 141.3mpg and stayed there
Driving with my clutch down fuel display eventually reached 141.3mpg and stayed there

So unfortunately the exercise proved nothing. The only difference was, as always, driving in gear the car slowed down quicker and had to be helped along earlier (thus using more fuel).

cyclonebri1

It's simple. Out of gear the car has to have fueling to prevent the engine from stalling. In gear, the fuelling is reduced to zero untill the revs drop typically to below 1100, whereupon the fuel program engages to keep the engine running.
It is a no brainer

Wig

cyclonebri1 wrote: »

It's simple. Out of gear the car has to have fueling to prevent the engine from stalling. In gear, the fuelling is reduced to zero untill the revs drop typically to below 1100, whereupon the fuel program engages to keep the engine running.
It is a no brainer

Except as I have shown, Vauxhall says not all cars have this feature, and no-one has yet been able to show that all petrol/diesel cars after a certain year has this feature (contrary to what vauxhall says) no-one says how many seconds it takes before fuel is shut off because no-one knows.

And even on cars with this feature, they will slow down quicker in gear and require accelerator pedal to be used to bring them back up to speed, thus using quite a bit of fuel over the same distance, compared to the car idling with "clutch in" using very little fuel and coasting along happily with very little resistance (by comparison) to slow the vehicle down.

iltisman

I used to commute 130 miles each way to and from work and I tried all methods to save fuel and knocking out of gear saved most fuel.I did this more to pass the 6 hours than save money and on one trip I freewheeled 33 miles.
I now expect incoming from the "you cant control your car" nutters.

hundredk

hothothot wrote: »

I ask because I was in a mates car which is automatic transmission and I asked him why he slipped it into N whilst going down the hill and he said to save fuel. is this good moneysaving and would it work in a manual gear car too?

This is more efficient than coasting in neutral but you need a manual car.

prowla

From the Highway Code:

Coasting. This term describes a vehicle travelling in
neutral or with the clutch pressed down. It can reduce
driver control because
• engine braking is eliminated
• vehicle speed downhill will increase quickly
• increased use of the footbrake can reduce its effectiveness
• steering response will be affected, particularly on bends and corners
• it may be more difficult to select the appropriate gear when needed.
The vehicle is also less likely to be heard by other road users.

dixie_dean_2

On a slightly different note, I did actually turn the engine off whilst coasting down a hill as was VERY low on petrol (and don't know much about cars). Crapped myself when I had to break and found the breaks stop working after a while with no engine on! I have a ford focus - don't know if this is the same for all cars.