Best method of coasting for MPG+?

[tomcoolj]

I'm pretty obsessed with fuel economy on my Fiesta 1.4 MK6.


When coasting up to a to a roundabout is it better to be in neutral gear, or have the clutch pedal down, i say for example 4th gear?


I'm asking this because I noticed that in Neutral gear the engine speed is 1000RPM, however in gear (clutch down) its at around 700RPM?


So, whats the best action to take in terms of fuel economy?

[Prince]

Hi tomcoolj, welcome to TorqueCars! I wouldn't really advise coasting... I would say that you should approach a roundabout in gear, but a gear you can move off in!

In answer to your question though clutch down is slightly better for fuel economy, but the difference won't really be noticable. I'm still not going to condone doing it though!

[HDi fun]

If you're coasting in gear with foot off the accelerator then surely there's no fuel delivery at all. as soon as you select N or declutch then the ECU delivers fuel to maintain idle speed.

I can verify this with the instantaneous MPG readout on my car's trip computer.

[pgarner]

like hdi says just lifting off the throttle cuts fuel delivary until around 1400rpm where the ecu will start again to prevent stalling

[waynne]

When the car is in gear there is no fuel going into the engine at all wheras in neutral or with the clutch down there is to prevent it from stalling. The engine braking caused though will slow up the car but I still think with this tradeoff it is better to coast in gear to junctions.

I have noticed that mpg increases if you momentarily lift off the throttle during a constant speed run. I can't explain how or why but at say a constant 47mpg if I ease off momentarily and then hold the same speed the mpg climbs to 50mpg?! Anyone else get this in their cars?

[HDi fun]

Can't say I have experienced that. Does it pan out in practice?

[pgarner]

it might be the vvt adjusting as its noticed youve eased off and no longer accelatating

[waynne]

It might be. Does yours do the same thing?

[pgarner]

yeah it jumps up a couple of mpg for a while the drops back again

[waynne]

Mine tends to stay up at least until I change from holding engine speed to accelerating again. The next part of this debate is:-

Is it better to accelerate to your cruising speed quickly or build it up slowly? I would say that because the car is more economical at the "cruising speed" this is the zone you want to be in so briskly accelerate to this speed as soon as possible. What do you guys find works best?