Rob
A buddy of mine was telling me that if you coast with a car, you'll get better fuel economy. He said that those hyper-miler guys coast to a stop - which is one way they get such high fuel economy. He's suggesting that when coming to a stop or driving down a hill I should put my transmission in neutral. This lowers the rpm of the engine, which lowers the amount of fuel being used.
This makes sense. What are your thoughts?
Ken
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Let me first start by pointing out that Chapter 318, Part 3, Article 197 of the British Columbia Motor Vehicle Act states:
"When travelling down grade a driver must not coast with the gears of the vehicle in neutral or the clutch disengaged."
Unfortunately, things are not as cut and dried in other provinces. Most information concerning this often controversial subject is contained in driver handbooks for new drivers. In every handbook I was able to obtain, the same theme is evident. Do not coast a vehicle in neutral. The reason is simple: the driver will not have the same amount of control as you would with an engaged transmission.
Alright Ken, legalese aside, there is no reason to place a transmission in neutral - for any reason - including increasing fuel economy (FE). Since the advent of micro-processor controlled fuel injection and drivetrain management, fuel delivery to the combustion chamber has been turned into a science. All manufacturers utilize Closed Throttle Deceleration strategies in their respective computer programs. This means that if the engine management system detects a closed throttle combined with steady or a reduction in vehicle speed and the transmission switch engaged (yet another computer sensor), fuel delivery is reduced to negligible or in some cases is turned off.
I did my own research on this subject. Every week I get to test drive a different vehicle. Over the past couple of months I've driven BMWs, Porsches, Hondas and Acuras. I just turned in an Acura ZDX. I mention this because many new cars have trip computers built into the instrument cluster. One of the features of these gadgets is an Instant Fuel Economy read-out.
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I live on the side of a mountain that has a two kilometre stretch of roadway on a 6 per cent grade. Using the ZDX as an example, I coasted down the hill in gear and in neutral.
The fuel economy numbers were very surprising. In neutral, I got FE numbers that ranged from 3.0 litres/100 km to 5.7 litres/100 km. But with the transmission in gear I consistently got 0 litres/100 km. That's hard to argue with, not to mention that if I needed to control the vehicle in case of an emergency, I was fully capable with the transmission engaged.
Ken, back in the halcyon days of carbureted engines, it might have made sense to shift to neutral, but now, it's not legal or safe and your fuel economy worsens. So gear down in control of your car as well as your fuel - don't coast out of control.