Coasting in Neutral is claimed to save you fuel but does it? And, should you rest your hand on a manual gear shifter?
AH, THE INTERNET. It and your best friend’s cousin’s dad are filled to the brim with information that sounds pretty good but is actually rubbish. Like some of the other myths we’ve covered, on the surface it sounds like there could be a little bit of truth in slotting neutral when you’re travelling downhill, taking the strain off the engine and letting momentum do its thing.
And the idea probably comes from bike riders. I’m not sure about you, but whenever I rode down a hill on my bike I used the hill as a chance to take a rest, because I’d just had to ride up the hill. Not pedalling and letting the bike roll down was like being rocket propelled. Unfortunately, it doesn’t work like this for vehicles.
See, when you take either your manual or automatic out of gear and into Neutral when driving down a hill you end up using, at the minimum, the same amount of fuel and perhaps more because the engine is still working and the fuel is still flowing. So the argument that you’ll save fuel doesn’t work, because you won’t. See, many modern vehicles will, when the system detects the vehicle is coasting (no load being applied via the throttle), shut off fuel supply or in those with the technology deactivate cylinders to reduce the amount of fuel being consumed. Thus, coasting in gear will in 99.9% of cases use less fuel than when you slot Neutral and try and rely on momentum.
Another issue with slotting Neutral is that you’ll have no ability to accelerate because you’re not in gear, all you’ll be able to do is slow down via the brakes and this lack of control will mean, potentially, you won’t be able to avoid a hazard.
One of the biggest issues of all, especially for an automatic transmission, is to shift from Neutral into Drive while travelling at speed. Basically, you’ll be slamming gears and bands together, and while it’s likely you’ll only damage some inexpensive parts inside the transmission it’ll cost a bomb to get to those parts. It’s the same for a manual transmission, only the meshing forces are different because you could slot top gear, whereas the automatic will go straight into first gear from Neutral.
So, don’t coast down a hill in Neutral in either a manual or automatic transmission, you won’t save fuel and you could break your transmission when you move from Neutral to a Gear, oh, and you won’t have any way of accelerating when you’re in Neutral, so your vehicle control is greatly reduced. More than that, it’s illegal to ‘clutch coast’ in all States and Territories in Australia; it’s considered “not maintaining control of the vehicle” and will cause an instant fail on your driving test and more if you have an accident and it’s revealed you were coasting in Neutral.
What about resting your hand on the gear shifter. This one relates to manual transmissions. From time to time we’ve all been guilty of using the shifter as a hand rest, whether you’ve lingered on the shifter between gear shifts, or are just hanging your hand on it in the same way someone might fat arm on the window sill.
This is not really a myth that needs busting, more a bad practice that can bugger your manual transmission, but given there was a tenuous link to clutch coasting we thought we’d mention it.
Besides reducing your car control (you should always be driving with two hands on the wheel) resting your hand on the shifter between gear shifts can result in premature wear of the transaxle shift forks. Basically, connected to the shift lever are forks which push a collar to engage a gear; by resting your hand on the shifter you could be applying ‘an amount’ of pressure to the forks that are thus being pushed slightly against the collars in the transmission, causing premature wear of the forks.
Short story, don’t rest your hand on the shifter because you could cause wear inside the transmission.
For my automatic, coasting in D with no throttle input is around 1200rpm on the engine, whereas coasting in neutral is 700rpm. How’s it possible neutral isn’t saving? If newfangled electronics can shut down cylinders in D-coasting, wouldn’t the same electronics shut down N-coasting as well?
For manual, how would shifting from neutral to top gear cause damages compared to shifting from 4th to 5th? I’d imagine there should be no damage to the transmission provided engine rev is matched by blipping the throttle?
Thanks
The issue is that when the vehicle is coasting in neutral it needs to use fuel to keep the engine ticking over and avoid stalling. Not an issue while coasting, but a big issue when you want to start going back up a hill as it will need the starter motor to restart the engine, and this at the same time as someone trying to re-engage the transmission…
Alternatively, when you’re coasting in gear, the engine is still connected to the wheels, so the momentum of the vehicle keeps the wheels turning which in turn keeps the engine ticking over. This allows the engineers to cut fuel completely when the vehicle detects this. i.e. Zero fuel use. Starting on up that next hill only requires the engine to reintroduce fuel. No starter motor, no surprise re-engagement, no worries 😉
Hope that helps.
(technically, stop-start technology could be employed to overcome part of the issue above, but in-gear coasting is much more practical.
it is not complete there. in neutral like you said it may consume a little bit of fuel to keep the engine running but we are taking advantage of the overall momentum of the vehicle when it is reaching the lowest point of the slope either to climb another hill or to get Extra distance covered.
it is definitely not safe but we are discussing about fuel efficiency on distance traveled.
however when we are in D, engine breaking slows down the car significantly and even in the highest gear so you don’t get as much momentum as if you were in N to climb the next hill or to continue extra distance.
I know that my English isn’t that good but i hope you understand what I am trying to say.
In gear coasting or engine braking creates a vacuum that sucks more fuel through costing will only use as much as an idle and won’t be reving and sucking fuel as you roll down the hill. If you know how an engine works you’d know that more fuel gets sucked through when you engine brake
Many modern cars except like…. Mondeo diesel. Leaving it in gear uses way more than popping it into neutral. Even its instant sous consumption gauge confirms the usage difference off-throttle vs neutral.
Even if it saves fuel, what is the real saving dollar terms? I suppose it depends on the opportunities to coast. I’ve done it in an old car when I was desperate to get to the next fuel stop (remember when most were not 24 hour and self serve?). I ran out of fuel just as I entered the servo’s driveway and coasted to the pump. Beats walking for k’s with a 5 litre can of fuel!
Any real saving would require the ignition to be turned off. I did that in my XW Falcon once or twice. You can’t do that in cars with power steering.
It’s not hard to prove that coasting down hill in gear saves fuel compared to coasting in nuetral. The Instant Fuel Use gauge drops to zero when coasting down a hill. Shift to nuetral and the injectors turn back on the keep the engine idling … and the display shows fuel usage.
The car coasting down hill has to spin the engine at a minimum rpm before the injectors turn off. It might be 1500rpm. If engine rpm drops back towards 1000rpm the injectors light up. Shifting back from 6th to 5th or 4th spins the engine marginally harder and the injectirs turn off again. Yes it’s an academic point. Or a point that might be important for economy run competitors.
Here’s a trap for young players. What happens if when coasting at 80kmh you engage 2nd gear (but hold the clutch in so you don’t buzz the engine). You buzz the clutch friction plate possibly hard enough to fling the friction material off!! And then you have to phone the boss “Chooker” to tow you back to the depot with the Dodge truck!
Depends on the fuel system, if injected it’ll save fuel because the EFI computer will close the injectors almost completely when you have no throttle input preventing the vacuum from sucking fuel through, but if it’s a carburettor it will create a vacuum in the intake manifold and suck a shit load of fuel through the carb
…….unless you have a modern one that does it all by itself.
Are there any new German cars that DON’T coast.
Appalling trait to have whilst motoring as I have seen this in action yeas ago and have been aghast to the scenario if the Brakes failed or the steering locked for some reason.
Most of these comments miss the most important point:- Coasting isn’t driving. If you don’t have instantaneous control over the car’s ability to accelerate out of unforeseen trouble, you ought to be in the passenger seat. Simple.
You missed the point that with many automatics the transmission oil pump does not operate in N , hence no flow through the oil cooler.
“It’s the same for a manual transmission, only the meshing forces are different because you could slot top gear, whereas the automatic will go straight into first gear from Neutral.”
Uhh…what? If you shift from neutral into drive in any auto vehicle since the 90s it’ll shift into the correct gear. Sometimes when I’ve coasted down a hill I’ve shifted it into drive and the engine will rev-match the transmission, although it’s not as good as rev-matching manually. Done right it will feel absolutely seamless.
In my town, there is a 3-mile 1% downgrade and then a 3-mile level grade road with no stop signs or street lights. I can usually coast this 6-mile road (unless there’s a strong wind) all the way in neutral in my automatic transmission car. So I’m only idling the car for 6 miles. If I coast down the grade in gear, then I need to apply the accelerator for 3 miles on the level. So if I leave it in gear, I use no fuel for 3 miles, but I use fuel for 3 miles. I think it uses less fuel to coast/idle than to coast in gear half-way and drive in gear half-way. The 1% downgrade doesn’t cause me to go over the speed limit coasting in neutral.
The person who wrote this article is an idiot. My car lasts 2 weeks before I need to fill gas when coasting and only 1 week if I keep gear engaged in drive. I have an automatic btw.
If you apply no throttle and roll in gear your engine will eventually be slowing you down (engine braking) this creates a vacuum in the intake manifold and possibly within the cylinder itself In turn this sucks fuel into the engine through the carburettor or injectors to be ingnited. The carburettor will suck alot more fuel through where as injectors will be limited to the same amount of fuel they use at an idle.
If you apply a small amount of throttle (just enough not to be engine braking) it will open the carb or injectors and use about the same amount as if you were engine braking except you’ll be going faster than if you were engine braking.
If you disengaged the gearbox or transmission, your motor will idle as though your sitting still at traffic lights, many newer cars automatically shut of the motor when in this state and older cars will just consume as much as they usually would at an idle.
The idea that the momentum of the vehicle helps the motor turn over and therefore requires less fuel to run is absolutely ridiculous, your engine is still firing and still consuming the exact same amount of fuel required to idle if not more (especially if it’s carbureted) if your car were using any less fuel the motor would stop firing which it clearly doesn’t otherwise you wouldn need to pop the clutch or crank the starter again.
Obviously your best option is to stop being a tight ass for one but go fuel throttle down hill as to increase your momentum so you don’t need to convert as much fossil fuel into energy and less energy into momentum to get up the next hill or down the road. Every time you convert energy there’s energy loss via inefficiency’s such as noise, heat and light in the motor, gearbox, diffs, tires and more
A basic understanding of a combustion engine and the year 10 science curriculum could of answered this but the article and many comments seem to be based upon personal opinion.
Wrong wrong wrong. Coasting downhill absolutely saves fuel. As a driver with many years of experience driving long distances I have raw data thta proves this. So, once again, you are wrong.