Slowing down in neutral vs in gear

[cos]

Doesn't slowing down/coming to a stop in neutral use less gas then slowing down in gear on a late model car? I've been throwing all my manual trans cars in neutral for yrs - I just figured it was less wear on the engine, and brakes are relatively easy to replace compared with a timing belt or chain.

 

[Quattro Pete]

Nope. On fuel-injected vehicles, when you're in gear and off the gas, the engine uses no fuel at all, as long as the rpms are above around 1200. So, if you know you're going to have to slow down or stop (like when coming to a traffic light that is red), it's more economical to do it in gear.

There's also a saftey factor that comes with being in gear. If need be, in emergencies, you can always quickly accelerate (like to get out of someone's way). If you're in neutral, all you can do is steer or hit the brakes.

 

[Cujet]

Quattro, While that is true for many cars, it is not true for all. Ford had a habit of opening the idle control valve when the throttle is lifted. This was an attempt to keep the catalytic converter hot.

Some Ford products actually do not slow down much at all under "lift throttle" conditions. These are the ones you always see the brake lights coming on in fairly smooth rush hour traffic. The drivers are unable to manage speed with the throttle alone, like most cars can. Certain year Taurus' are particularly bad.

 

[Palut]

I always leave my car in gear when slowing or stopping, but I don't downshift. This way there is no wear on the clutch or transmission, less wear on the brakes, and I figure that worse case I'm using the same amount of fuel as idling to a stop. Doing this allowed me to do 40,000 miles of pizza delivery averaging 28-29 mpg in a car rated for 25 city and has allowed my brakes to last forever. My front brakes were on the car when I bought it, I've had it for 98,000 miles and they still have 45% of the pad left!

 

[Quattro Pete]

Cujet, just to make sure we're on the same page: We are talking about cars with manual transmissions here. Are you saying Fords with manual trannies don't slow down when in gear and off the throttle? What happens when the car is in neutral? Does it run on insanely high rpms? Also, just curious, what % of Tauruses came with manual trannies? I thought that was a rarity...

 

[toocrazy2yoo]

I slide the car out of gear in my 5 speed on a long drift into a stacked up light, or an intersection I know to have a long red.. No clutch, just ease it into neutral and coast. If the way ahead clears, back into third, fourth or fifth, no fuss, no muss. It's the right lane, not like I'm impeding traffic..

 

[Jim 5]

My fuel economy indicator in the 330ci shows the highest possible fuel economy slowing down in gear (manual trans). The fuel economy is significantly higher than in neutral with the brakes on.

 

[brianl703]

Quote:

---

Are you saying Fords with manual trannies don't slow down when in gear and off the throttle?

---

I hope not, because that isn't true (based on several Escorts, a Mustang, and a couple of Contours, all with manual transmissions).

 

[Cujet]

I was just making the point that some cars do hold the idle control valve "more open" than idle conditions under decel. This a software function, and drivers may or may not be aware of it. There are some manual trans cars that do this also.

I personally like shifting into neutral and coasting to a stop, as I have a few rural spots this works well at.

Please do not misunderstand my point. I was only trying to say that not all cars cut fuel upon throttle lift.

Chris

 

[Quattro Pete]

Understood. I guess I wasn't aware that some cars do that.

 

[brianl703]

My understanding is that Ford vehicles gradually close the idle air control valve upon decel so as to act as a dashpot.

 

[mazduh30]

Thought it was illegal to have a motor vehicle in neutral when driving or coming to a stop?

 

[brianl703]

It is in Virginia. Dunno about anywhere else. A 3-point violation, as I recall.

 

[Cujet]

""Thought it was illegal to have a motor vehicle in neutral when driving or coming to a stop?""

OOOPS, I meant to say, I never do this.

Chris

 

[Quattro Pete]

What's the reasoning behind this? Inadequate control of the vehicle?

I mean, I don't do this myself, but to give out points for this is a bit harsh...

 

[OriginHacker21]

I have ScanGuage and ... when I slow down by downshifting it shows considerably less LOD (load) on engine than if I put it in neutral. In neutral (idle) the LOD is 23-30%. When I am downshifting the LOD is 7-10%. I would imagine that less load = less fuel being used. Interesting how much load there is on the engine to keep it idle.

In a manual - I was under the impression that when stopped you don't want to leave it in gear (with the clutch in) - so I usually have it in neutral when sitting at a light.

In a manual - if I am coming up to a stop sign or a light and I don't need to downshift (feeling lazy/no one behind me) - I'll put it in neutral and coast. The difference in MPG can't be that much... Never knew it was illegal to do that in some states. Wonder how they check this?

 

[brianl703]

If I had to take a guess I'd say it is because a car's engine can stall while coasting in neutral, resulting in the loss of power steering and power braking, making it that much harder to avoid an accident. It is also harder to avoid an accident if you must put the car back into gear to accelerate (if accelerating would help you avoid the accident).

Some say it's because older cars had 4-wheel drum brakes which are fade-prone and coasting down a hill in neutral could cause a loss of control due to brake fade.

It might also be because it is easy to loose control of a heavy-duty truck if you go down a hill in neutral. The truck will speed up if the brakes overheat, and it will be impossible to put it back into gear for engine braking. Perhaps they decided not to differentiate between the two (heavy-duty trucks and regular cars/trucks) for the purposes of this law.

 

[Patman]

That is crazy to have a law against slowing down in neutral! In my Corvette if I'm driving in light snow or ice I find the car slows down much quicker at lower speeds if I throw it in neutral, as then the engine isn't fighting against the brakes.

 

[brianl703]

Here's the actual law:

§ 46.2-811. Coasting prohibited.

The driver of any motor vehicle traveling on a downgrade on any highway shall not coast with the gears of the vehicle in neutral.

(Code 1950, § 46-218; 1958, c. 541, § 46.1-200; 1989, c. 727.)

Looks like it's ok on level ground, not that we have much of that in this state.

 

[Quattro Pete]

Quote:

---

not that we have much of that in this state.

---

Oh how I miss those spirited runs on curvy and hilly VA and WV roads. I am dying of boredom driving down here in FL... no hills, no curves... just going straight.