Hypermiling in a Diesel

[Jay2TheRescue]

I agree. Neutral is very effective on diesels.

[Bolgerwalsh]

I coast in neutral as often as I can in my 2010 Bravo with 104k on the clock. It seems to work okay for me. Having said that, I rarely go above 95km/hr on the motorway.

[Jay2TheRescue]

There is a fine line between DFCO and Neutral coasting, and it is different on each vehicle. Knowing when to choose which procedure is a big key to maximizing your mileage.

[jostlehim]

On HDi engines, which most are now, then coasting in gear but no throttle will use no fuel at all. Coasting in neutral uses some fuel, so you end up using fuel going downhill. This is, however, for systems with a fixed connection between engine and gear (e.g. manual, DSG etc). I'm not sure whether that is true for a torque converter, as you aren't able to push start these either.

So, you need to weigh up the ∂fuel used for acceleration (assuming you haven't been travelling at your desired speed anyway) vs the ∂fuel used keeping the engine idling in neutral.

[trollbait]

Many torque converter automatics do have fuel cut off while coasting in gear. If all new ones don't do it now, they will soon for better CAFE numbers.

Older automatics will take some testing, and likely a scangauge or equivalent, to determine if they do. Then they may only do so under limited circumstances.

[Jay2TheRescue]

I realize that there is fuel used in Neutral. The problem is that DFCO does slow the vehicle down. Moderate descents where the vehicle would lose speed if left in gear (and then requiring extra throttle to get back up to speed) is where Neutral would be best. If the descent is steep enough that you can go down in gear and not lose speed, then DFCO is your better option. It all breaks down to how well your particular vehicle coasts.