Switching to neutral while driving downhill on automatic?


#1

I tried to call to ask this question: is it good practice to shift to neutral, while driving downhill on automatic transmission? the owner manual does not recommend, would like to know why.
it makes sense to save gas, while doing this. (i used to do it while driving manual)


#2

No it is not a good practice.
In addition to being illegal in many states, it DOES NOT save gas on a modern car.

If you want further explanation, you can use the search function on this board to locate the many, many threads on this exact topic.


#3

It’s never really a good idea to shift to neutral when driving downhill, regardless of the type of transmission you have. In neutral, you’re just freewheeling downhill and don’t have as much control over the vehicle. Depending on the steepness of the downhill grade, and whether or not you’re towing/hauling, if anything you should downshift to a lower gear; this will save A LOT of unnecessary wear and tear on your brakes, because you won’t need to use them as much to control your descent. In other words, what you save in fuel costs by freewheeling downhill in neutral will most likely result in the premature need for a major brake job costing BIG BUCKS. I would most definitely NOT recommend the practice of coasting down any hill in neutral.


#4

“In other words, what you save in fuel costs by freewheeling downhill in neutral will most likely result in the premature need for a major brake job costing BIG BUCKS.”

That’s half-right.
Yes, doing this will result in more wear and tear on the brakes, thus resulting in higher repair costs. However, it DOES NOT save gas on a modern fuel-injected vehicle.

So–the OP is wasting money in two ways.
Not a good move, from any perspective.


#5

I concur with VDCdriver 100%. Shifting to neutral while going downhill does not save fuel and it puts the driver and passenger(s) at risk if the engine died suddenly.


#6

Your transmission pumps its oil from the front. In neutral the front pump stops pumping yet the drive shaft is still spinning like mad from the back.

  • Just how many components are now starved for oil ? ( different answers for each trans type )
  • How long of a coast will cause damage ? ( that beautiful long downgrade into Albuquerque called 9 mile hill…is too long. )
  • how many short coasts and minor damage will it stand before you notice ?
  • Are you the gambling type ?

As stated, most newer vehicles gain nothing from that practice.
Why ?
The computer keeps the rpm up where it was so as not to slam into gear later when you forget to increase the rpm to match mph.


#7

RE: Does shifting to neutral save gas
While the prevailing thinking is that it doesn’t, I’m no longer certain that’s the case.

We all seem to agree, with recent vintage cars, that the injectors are shutoff during deceleration, and that saves fuel (over older designs where the injectors did not shut off).

However, I’ve recently seen several claims from “Hypermilers” who assert that they can save more fuel by shifting in to neutral. If a car is left in gear, engine friction will reduce the distance a car can coast - which is the root of their claim.

Hypermilers claim the amount of gas they use idling the engine while coasting in neutral is less overall than leaving it gear (where the injectors are shut off for a smaller coasting distance, and then the accelerator is needed).

I’m very much against coasting in neutral. But in my mind, hypermilers make a claim that I need to understand more before saying shifting into neutral doesn’t save gas.


#8

“I’ve recently seen several claims from “Hypermilers” who assert that they can save more fuel by shifting in to neutral. If a car is left in gear, engine friction will reduce the distance a car can coast…”

Don’t hypermilers also do things like shut off the engine? Some of the things they do seem crazy to people who like air conditioning and who put safety first.