In some cases coasting in neutral will save fuel, in others it will not. This depends on the specific situation.
If you're coasting down a hill to a stop, then it's better to coast in gear to use approximately no fuel. If you're coasting down a hill to long level stretch of road it's better to coast in neutral to obtain kinetic energy. If one wants to follow speed limits it's sometimes necessary to first coast in neutral then use engine braking at the bottom of the hill.
The optimal strategy in all cases is actually coasting in neutral with the engine turned off, and then starting the engine when you need to increase your speed. (This advanced technique may be illegal, though).
Slight tangent but my car could fail the test then :) It automatically coasts (yep, engine back to idle and everything) when in it's most economical automatic mode.
Haha, yes, that's why I specified it as a tangent. I did think it was a weird feature though as I knew the controversy over coasting :) And yep, a red AMG A45!
Apparently Mercedes call it "glide mode" or "gliding mode" depending which bit of marketing you look at. I couldn't find a technical description though (beyond what you already said).
I've seen it called "sailing" (and the icon on the dashboard is of a sailboat). See https://www.youtube.com/watch?v=S4N8BlXro9w (see 48 seconds in) - but this could be a language difference between territories.
But if you're coasting down a hill and not braking, your engine is idling and you're making use of gravity. The engine will be turning over at ~1000rpm instead of 2000rpm in my diesel.
Understandably it is dangerous as you are not in control of the transmission and therefore the wheels, hence the failure in the UK. But I got through some incredibly scarce times by coasting a bit on the commute to work...
With automatics you would need to brake down the hill to stop the car "running away" as it wouldn't engine brake automatically to compensate for gravity's effect.
With automatics you would need to brake down the hill to stop the car "running away" as it wouldn't engine brake automatically to compensate for gravity's effect.
Most automatic transmissions (or at least the ones I've driven, which arguably is not more recent than late 90s) have low ranges where there is engine braking. That's the exact use case for them. Automatic doesn't (or didn't) mean that you must never shift manually.
Automatic transmissions in large vehicles like trucks and buses usually don't have freewheels either, so there is always engine braking.
> The engine will be turning over at ~1000rpm instead of 2000rpm in my diesel.
Right, but when you're coasting you're burning fuel to turn over, unless you have a perpetual motion engine. Whereas engine braking (on a car with an ECU i.e. one made since 1996 or so) you could be doing 2000rpm but burning no fuel (gravity is turning the wheels which are turning the engine).
Sure. Turning the engine is going to take energy one way or the other. But you can use energy that would otherwise be wasted heating up the brake pads rather than energy from burning fuel.
So if you're coasting you're spending fuel to increase your speed (relative to what you'd do by staying in gear). In the situation where you're considering coasting that's probably not a tradeoff you want to be making.
Every automatic car I've ever seen has had the ability to downshift to engage engine braking. (Even the CVT in cars like the Prius has an engine braking mode.) I've seen advocates of manual transmissions cite a lack of engine braking as a reason to switch in multiple conversations, so I've gotten the impression that a lot of people just aren't taught how to drive an automatic properly. (Do they not talk about this in driver's ed? I don't even remember anymore.)
> Even the CVT in cars like the Prius has an engine braking mode
Well, of course a hybrid has engine braking - that's kind of pivotal to the whole hybrid design. It freaked my wife out the first time we went down a 7% grade in ours in 'B(raking)' - once the battery charged holding down the brake pedal caused the second MG to disengage from the transaxle and spin at max RPM's to bleed off the excess energy.
But yes, every automatic car I've ever been in has had engine braking as well - going down the same grade by mother will shift her Chevy Impala into '3' and can easily coast down the same hill only applying the brake to turn corners.
Would be nice if our Prius didn't require holding down the brake pedal, but in a way I think it plays into the natural instincts of a driver to do so - but it's a habit that can get you killed driving a manual or standard automatic transmission by overheating the brakes, so hopefully my wife doesn't go down any grades in a car other than our own without me.
The e-brake in my automatic Volvo is shot, so my wife and I were practicing how to engine brake down from 50 km/h to a crawl. She was surprised that she was never made to learn this in driver's ed.
My current car has "regenerative breaking" that charges the battery(not a hybrid, just a normal BMW). I haven't tried any testing without cruise control on, but with cruise on it will definitely do a little breaking on highway downhills to maintain speed.
Every generation of car is getting better at all these things, so statements about efficiency almost all need a "cars built prior to 20XX".
Honda Civic 06 i-Drive (CVT) will shift into lower gear, thus engine brake, if you brake hard enough to trigger the shift threshold. And you can go directly into manual override whenever you hit the wheel paddles or push/pull the stick.
In the UK you will fail your driving test if you coast, and in some countries / states it is illegal - with good reason.
Just google it - not a single article supporting your argument.