Shifting into Neutral down steep grades to save fuel worth it?

Is shifting your BMW into Neutral

  • Yes, I do it or would recommend it.

    Votes: 3 33.3%
  • No, it will harm the vehicle or doesnt seem like a good idea.

    Votes: 6 66.7%
  • I am indifferent to it/I don't know enough to answer fairly

    Votes: 0 0.0%
  • Who cares? I don't care about our oil dependence, gas prices, or the environment.

    Votes: 0 0.0%

  • Total voters
    9
#1
I've been wondering if shifting into Neutral when coasting down a hill in your BMW is a good or bad idea? It seems that opinion is mixed as to whether or not it causes harm to the vehicle, especially if you take your foot off the gas when you shift into N and then back into D.

I have noticed in my X3 3.0si that since the vehicle comes equipped with Hill Descent Control that the engines rpms are around 2750 to 3000 when descending at say 70mph, resulting is the car using almost as much fuel as if it were driving on a level road. At the same time I noticed the X3 can make it up grades as steep as 30% without up shifting which is impressive as it holds 65 or 75mph.

I have noticed that the X3 gets roughly 22mpg driving normally not caring about gas, and speeding where possible such as 74 in a 65 or 69 in a 60 or 84 in a 75. Yet on a drive home which was roughly 300 miles that included some steep mountain hills that went from 2,000ft to 5,000 to 3,000 to 1,000 to 2,000 and so on over the duration of the drive, I decided to shift into Neutral when descending these inclines. The result:

An amazing 28mpg average, 5mpg more on average for 300 miles is significant. Considering I would use roughly 12 gallons, that amounts to 50 extra miles, an easy savings of $15 and a good 3 gallons less consumption which is better for the environment. All of this raises the question[???1], is it harmful or not?
 
#2
No never shift an automatic into netural while moving as this can be very hard on the torque converter and other componets. Besides coating downhills is illegal in most states.
 
#3
You're referring to a technique called Hypermiling. This is just one method of increasing your fuel economy. Check out this web site. The top of the page talks about EPA calcs, go further down the page to read about hypermiling techniques.

After reading your post esrlier this week, I decided to do some tests. I was traveling on business this week and had a Volvo S60 2.5T rental car. Since it's not my car, I tried a few different things to evaluate the transmission (didn't do this to check mileage),

- I put it in neutral, coasted for .1 mile or so, and put it back in drive without stepping on the gas at all. Each time I did this the transmission made a loud clunk and the car bucked. Obviously the car was less than happy with this treatment.

- Did the same, but BEFORE shifting into drive, I rev-matched engine to the road speed. That is, I stepped on the gas and reved the engine to roughly the right RPM, and then shifted. There was a lot less noise and buck, just a little.

I repeated these tests 7 - 8 times, and got the same results. My unscientific test leads me to believe that if you do this at all with an auto, it is vital to rev-match to minimize excessive pressure and shock.

My opinion is that it might be OK with a big 'ol Chevy truck transmission, but with all the reports of transmission issues with bimmers over the years, I will not do this with my 330. The hypermiling site also warns that this can be harmful to the tranny.
 

Bmw 325i 7803

1000 Post Club
#4
You're referring to a technique called Hypermiling. This is just one method of increasing your fuel economy. Check out this web site. The top of the page talks about EPA calcs, go further down the page to read about hypermiling techniques.

After reading your post esrlier this week, I decided to do some tests. I was traveling on business this week and had a Volvo S60 2.5T rental car. Since it's not my car, I tried a few different things to evaluate the transmission (didn't do this to check mileage),

- I put it in neutral, coasted for .1 mile or so, and put it back in drive without stepping on the gas at all. Each time I did this the transmission made a loud clunk and the car bucked. Obviously the car was less than happy with this treatment.

- Did the same, but BEFORE shifting into drive, I rev-matched engine to the road speed. That is, I stepped on the gas and reved the engine to roughly the right RPM, and then shifted. There was a lot less noise and buck, just a little.

I repeated these tests 7 - 8 times, and got the same results. My unscientific test leads me to believe that if you do this at all with an auto, it is vital to rev-match to minimize excessive pressure and shock.

My opinion is that it might be OK with a big 'ol Chevy truck transmission, but with all the reports of transmission issues with bimmers over the years, I will not do this with my 330. The hypermiling site also warns that this can be harmful to the tranny.


You're right, I guess hypermiling is something I got into when I had the Hybrid and was less than impressed with the fuel mileage. It was as if getting the EPA's 42 and 45 rating was very difficult if not impossible. Although I rarely if ever put the car into neutral and let it coast.

On the X3 however, there seems to be a built in feature where you cannot shift the transmission if the rpm's are too high and if you do the computer will not engage the gear unless you are within the rpm specification. I also never heard a clunk, perhaps the Volvo has a different type of transmission or it was abused as it is a rental car?

The consensus does seem to be that this is a bad idea, and I have not done this by habit, I just felt I'd report my findings and see what the consensus was.
 
#5
I think the consensus is that it is a bad idea in a new car. I cannot find a sole who thinks this is a good idea, not to mention the legal status.
 
#6
I think the consensus is that it is a bad idea in a new car. I cannot find a sole who thinks this is a good idea, not to mention the legal status.
I agree, but I must admit I can't help it but, the next time I am descending one of those huge several miles long declines, I will inevitably drop it into neutral and ride the brakes. If it's done in such moderation, the transmission makes no jerking sounds or clanking sounds, and the brakes are free... I say why not. In any other case, I wouldn't recommend it I suppose unless it was a standard.
 


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