Coasting in Neutral Vs. Coasting in Drive observation

[spyghost]

unfortunately, my engine is a carb engine

[NeilBlanchard]

Hello,

Really? A carbureted engine in 2000? I thought that the last carbureted vehicle sold in the USA was the Izuzu P'Up?

Oh wait, you are in the Philippines.

Sure -- then idling the motor and using your brakes is going to be the best way to save fuel.

[Jdublu]

I just added a scangauge to my 2002 Saturn Vue. In neutral it shows the throttle position as 1. As soon as I put the car in drive the TP goes to 2. When sitting at a light, you can see the MPG drop steadily about .1 MPG per 15 seconds when in drive. In neutral, the MPG drops .1 per 30-40 seconds. The instant mpg indicates approximately 50% higher when coasting in neutral than in gear.

Jay

[xbUser]

I had this question before when I know coasting in gear cuts the fuel above certain rpm. Which technique is better in which situation? My conclusion is following the traffic!! Use coasting in gear technique as engine brake to control the speed. Your safety is #1, other safety is #2, mpg is #3.

[PaleMelanesian]

I try to keep a buffer so I never have to use the brakes or do engine braking in traffic. There's definitely an art to it, but it's generally possible. That makes the choice much easier - use neutral.

[extragoode]

Originally Posted by PaleMelanesian

I try to keep a buffer so I never have to use the brakes or do engine braking in traffic. There's definitely an art to it, but it's generally possible.

It depends entirely on the other vehicles in traffic. Around here, if I leave a buffer of more than two car lengths some jerk merges into it!

[PaleMelanesian]

2 car lengths isn't much of a buffer. A single jerk can cut it in half, like you said. Now 10 car lengths... a single jerk takes out only 10% of your buffer.

It is possible. I've driven in Houston, Dallas, Chicago, San Francisco and San Diego in recent months. It's harder in busy cities, true, but it's still possible.

... and in my experience, the jerks that jump into your buffer are just as likely to jump back out a few seconds later.

[extragoode]

Originally Posted by PaleMelanesian

2 car lengths isn't much of a buffer. A single jerk can cut it in half, like you said. Now 10 car lengths... a single jerk takes out only 10% of your buffer.

It is possible. I've driven in Houston, Dallas, Chicago, San Francisco and San Diego in recent months. It's harder in busy cities, true, but it's still possible.

... and in my experience, the jerks that jump into your buffer are just as likely to jump back out a few seconds later.

I was using that as the low end extreme, meaning that's all it takes before someone jumps my buffer. If I leave a buffer of 3 car lengths, two jerks will jump in. 4 lengths, and I get 3 jerks and so on. That's just my experience. Also, my commute purposely avoids the freeway, so I'm talking about 4 lane, one way 35MPH speed limit in which everyone is going at least 40.

[saunders1313]

This is all very foreign to me. I have a motorcycle with a carb on it. So I'm not understanding how engine braking can give you better fe than coasting in neutral. Maybe it's just me, but I've coasted a lot using engine braking (before I knew what ecodriving was) and a lot just in neutral, and just by listening to the sound of the engine you can notice a huge difference in RPMs when engine braking. Is this something on newer cars? I had a '07 Dodge Caliber and it seemed about the same results. If fuel is usually cut off from the engine during engine braking, how does it continue to run?

[PaleMelanesian]

Carburetors usually don't do fuel cut. In that case, Neutral is the best option, period.

On cars with fuel cut programmed in, it's the wheels driving the engine. Just like the engine driving the wheels in normal operation. There's a direct (through gears and all) connection between the pistons and the wheels. When you let off the throttle, the car's momentum will keep the wheels turning. That, in turn, drives the engine. It'll keep turning whether or not there's any fuel burning, so why use any? The control unit turns off the injectors.