I read on some autowebsites that some people drive / switch their cars in NEUTRAL Gear:
1) on downhill
2) before approaching a stoplight
3) before coming to a complete stop.
to save some gas and thereby increasing MPG.

My question: Will this actually save gas and have bad effect on the car's transmssion or engine or any mechanicals ?

Please reply.Thanks.

 

I'm not sure about the benefits, but I was told in a defensive driving course (after going a tad faster than I ought've) that it's illegal in Texas. No idea whether other states take this position...

 

There was an article on this topic in the May 2008 issue of Road & Track magazine.
"Coasting is a boon to fuel economy, for sure, but staying in gear might even be better. That's because the engine is supplied with idle speed fuel whenever the transmission is in neutral. However, if left in gear, the computer will likely turn the fuel injectors completely off for momentarily infinite fuel economy. The injectors will eventually re-open to maintain at least engine idle speed, so if the gradient is shallow, then coasting in neutral will garner the least fuel consumption."

 

Coasting downhill is dangerous. Much better to use engine braking in gear for more control.

If you have a BMW with Efficient Dynamics such as the LCI, it does the gas saving for you. None of this neutral nonsense is required.

 

It's certainly unsafe. If you need to suddenly apply power you will be "dead in the water".

 

In the UK that will make you fail your driving test.

 

I don't understand how coasting in neutral up to a stop would save you gas. The thing's at 0 throttle position anyway, and engine braking doesn't burn any more fuel than neutral.
Coasting in neutral down a hill is dangerous. As other have written, you haven't the ability to speed up if needed, and the car's handling is actually compromised due to the trans being disengaged. With it in gear, the rear drags, taking some of the weight off the front. If you ever watch road racing, and see a bike get a false neutral coming into a turn, they always have to bail on it, and ride straight off. Othewise the front would have too much weight, and the thing would lose traction and low-side. No way to take some weight off with the trans coming in, and no way to shift weight to the rear with the throttle coming out. Just an example...

 

I agree, a gear should always be engaged when you are driving.

 

In most fuel injected cars fuel injectors are turned off when coasting in gear (at least for a manual tranny). I know this for a fact because you can see this with a scan tool. So you would use more fuel in neutral than if you were in gear, when coasting to a stop or on the hwy.

In a car with a carborator this is different story.

 

+1. Newer cars have EFI (Electronic Fuel Injection) system which does the gas consumption adjustments for you. It's the same concept as NOT needing to warm up your car for a few minutes when you first start it in the morning.