Hello everyone and welcome in this video
we're gonna be answering the question is it more efficient to coast in neutral or
Engine break when going downhill and really this will apply to either automatic or manual
Transmissions in this particular case I am in a manual transmission
2016 Subaru Crosstrek
And we're really going to be ignoring you know any of the negative consequences of doing either one of these all we're really
Focusing on is efficiency so whichever one's safer that kind of thing this isn't the place for that discussion
We're literally just talking about which is more efficient now. There are two different scenarios
I want to talk about to answer this question because of course the answer is it depends and so the first scenario
We're going downhill
We're starting at the top of a hill
And then we're going to stay on this simple straight path
To the bottom of that hill and then we're stopping there at the bottom and in this scenario the more efficient thing to do is
To leave it in gear and the reason why is because when you leave it in gear and you take your foot off the gas,
And you're just using engine braking your engine
No longer injects fuel so you're using absolutely no fuel as you go down the only thing that's keeping you going is
Gravity and inertia and your engine is actually working against you to slow the vehicle down so the engine is rotating yes
But it's rotating because the wheels which are connected to the transmission are forcing it to and it's eventually going to slow the vehicle down
To a stop if you run out of hill and so just a quick demonstration of that. I've got a you know video
That's showing my live fuel economy, and if I let my foot off the gas completely
You can see it goes to ninety nine nine
Which is the maximum it'll ever read and that's because the fuel injectors are shut off if I put my foot on the throttle
It'll go back down and you can see that
It's using fuel so the instant I touched the throttle you can see it is using fuel
but if I let off completely
It goes to 99.9 quits injecting fuel and you can see that that's an efficient way to run
Now if I do put it in neutral it now has to take care of that engine and use fuel to keep it running
So you can see that if I go slow enough so
Now I'm doing 25
And it 80 miles per gallon rather than 99 if I were to put it in gear so let me put it in gear
Still staying at 25, and you can see it goes up to 99.9
Because it is now shut off that fuel injection so to keep it idling it has to use some fuel and so that
Results in us seeing you know that fuel economy of 90 miles per gallon or whatever it may be
It's obviously not using much fuel it doesn't take much fuel to keep an engine idling, but if you're traveling really slow
And you can see that will of course start to drop because the amount of fuel you're using relative to how quickly you're moving has
Increased okay so our second scenario is there possibly a scenario where coasting and neutral would be more efficient and there absolutely is
So let's say you start at the top of a hill, and then you come down quite a bit
And then you go up another smaller hill and then you go down
And then you go back up another smaller hill and then you go down and you back up another smaller hill and so on
until you finally reach your destination
well if you put it in neutral as you're coming down that first big hill you're going to gain a lot more speed than if
You were to leave it in gear so by leaving it in gear yes, you won't use any fuel
But then you'll get to the bottom of that hill and you'll have to use fuel to work your way up over
It versus if you were in the car. That was coasting in neutral has now reached a high enough speed
I mean this is basically how
rollercoasters work
they have enough gravity to get over that next smaller hill that they go on and so the same thing applies in this scenario with
your car you can leave it in neutral you're not using much fuel and
You're able to use all of that
Momentum from the first hill to go over the second one and the third one and the fourth one and so on so in
scenarios where you're going down a steep hill and
You know you want to get over the hill in front of you using the least amount of fuel
Coasting a neutral can allow you to build more speed and therefore do it now you might exceed the speed limit
It's not exactly safe to be in gear because you have less control of your acceleration obviously
So there are reasons why you don't want to do it but from an efficiency standpoint
It would be more efficient to just coast in neutral in that scenario and roll over those smaller hills rather than use the engine
To you know put it in gear
And drive up those smaller hills which of course will use a decent amount of fuel, but as you can see here
You know we're just kind of coasting down at around 30 30 so miles an hour
The a/c is on so it's you know also running the engine for the air conditioning
and we're getting about 85 miles per gallon of course if I were to then stick it in third gear and
Release the throttle completely you can see you know it can continue to run that air conditioning even without using any fuel
simply by using the inertia of the vehicle to help rotate that engine and we're getting you know infinite miles per gallon because we're not
Using any fuel so as always to answer the question you know these kind of hypothetical questions
Which one is more efficient the answer is always it depends if you guys have any questions or comments feel free to leave them below
Thanks for watching!