Driving in Neutral good or bad?

hi - I have a habbit of driving in neutral whenever possible. I do this just to save petrol. For eg - when I see that i am approaching a red signal, i put my car in neutral and let it drive itself. Whenever I am coming off a fly over, while i am declining, i put my car in neutral.

Obviously I do this based upon the traffic conditions and not all the time. I think this helps in saving petrol. But I have questions about this technique -

1. Is there any harm in doing this? Is there any impact on braking while the car is moving in neutral?

2. When the car is in neutral, does it consume no petrol at all?

Nilesh

-I'm not sure how but too much driving in neutral can damage the catalytic converter

-It is detrimental to the transmission of cars that have A/T

-You are left with no 'engine braking' NEVER do this, especially on downhill slopes

-Even if your car is in neutral but the engine is running, fuel will be consumed.

Hi Bhejdo - thanks for your answer. What would be the right forum for this question? I will move it there.

Similar kind of practice I follow with my bike. I always judge the amount of traffic or any crossing from about 200 meters and then accelerate till the speed of 60-70 and then decelerate fully and allow the bike to roll till the speed of 20-30. Then gear down to 2nd 0r 3rd according to the speed.

Gouri - Quick Question. Is there any diffrence in getting your car/bike in neutral vs taking your foot off the accelerator and let the car drive itself? from the petrol consumption standpoint, is it the same for both the cases?

I don't know too much technicals but I find it hard to put my bike in nutral at 70 KMPH. So I let it roll in 5th Gear only.

Don't know about after effects. But I have seen hike in my FE drastically. Earlier I was getting average of 40 but now I am getting 50 now.

If any expert can advice.

Modern ECUs put the IC engine into a complete fuel stop when the vehicle is above a certain speed (35 kmph, implementation dependent) - This is called as Deceleration Fuel Cut Off (DFCO) - this is useful when going down a mountain slope, where sustained braking is not recommended for brake pad wear concerns. When coasting in gear, the speed is not allowed to increase because of engine acting as a speed dampener. This is called engine braking, and is recommended over coasting down in neutral with heavy use of brakes for limiting speed.

DFCO is zero fuel consumption while the phenomenon is happening, but it slows down the vehicle a lot. So from pure FE perspective, it is not really very good. You would need fuel to speed up to the desired vehicle speed when you snap out of it.

Coasting in neutral results in small constant expenditure of fuel, for maintaining the engine idle RPM. The advantage here is the engine is completely disengaged from the wheels, and the wheels spin only under vehicle inertia. Substantial savings are possible when coasting in neutral - I can generally (depending on terrain) go about 600-700 meters at one go when slowing from 70 kmph to 40 kmph  => This is my default mode of highway travel.

When 40 kmph is reached, I shift to 4th gear (appropriate for the vehicle speed) and accelerate to 70. Then rinse and repeat. I can get upto 20% better FE using this technique, as opposed to steady state driving in the top gear with the optimal speed/throttle combination. So I can confirm Gouri's observation mentioned above.

OT: A more extreme way of saving fuel is to switch off the engine when coasting, but I advise people to research carefully and understand the safety concerns when doing this extreme stuff. Not for the beginners anyways.

I am no way any expert, but have tried a few things in the name of FE, and therefore tried to answer in spite of a call for expert opinion by Gouri. Hope you will excuse me.

Great details Krishna. Like you rightly pointed I wouldnt recommend switching off the engine completely because breaks dont work in that case and one of my colleagues ended up hitting a car in the front with this technique.

Driving the vehicle in neutral will result in over usage of brakes leading to overheating and consequent brake failure.  Driving the vehicle with the engine switched off is very dangerous, especially in modern cars, where brakes do not operate, when the engine is switched off.  Please read the owner's handbook carefully, where no such advice is given just to save some fuel at the risk of not only the occupants' lives, but also other road-users' lives.  While driving downhill, NEVER drive in neutral or with engine switched off.  While climbing down, use the same gear, which you used to drive uphill, that way, you use the engine brake to the maximum extent and the vehicle will be in your control.  Follow the instructions given in the owner's handbook scrupulously.  Our lives are more precious than the fuel, we can't afford to lose!

So krishna do you want to say that my technique is safe for me and my bike?