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Random question. Just something I always wondered

  • 23-01-2012 8:48am
    #1
    NIMAN
    Registered Users, Registered Users 2 Posts: 34,694 ✭✭✭✭


    I often travel down a steep hill in my car.

    If I keep it in gear in 5th, the revs are are approx 2100/2200 rpm and I end up tapping the break to keep it at the speed limit of 80kph.

    If I put it in neutral and coast down the hill the revs drop to 800rpm.

    Is this saving petrol or does the engine use the same amount?


Comments

  • #2
    Mr Benevolent
    Closed Accounts Posts: 12,456 ✭✭✭✭Mr Benevolent


    Keeping it in gear, foot off the clutch, saves more petrol. The feature is called 'cutoff overrun' and shuts off the fuel injectors. Doesn't work below about 1500rpm.


  • #3
    TestTransmission
    Registered Users, Registered Users 2 Posts: 19,106 ✭✭✭✭TestTransmission


    NIMAN wrote: »

    If I put it in neutral and coast down the hill the revs drop to 800rpm.

    That's a very dangerous habit to get into imo


  • #4
    Littlehorny
    Registered Users, Registered Users 2 Posts: 2,351 ✭✭✭Littlehorny


    I think they covered this on top gear a few years back where if you coast in gear like down a hill with your feet off all the pedals then modern engines dont use any fuel whatsoever. As said before it is a much safer way of coming down an incline aswell.


  • #5
    TestTransmission
    Registered Users, Registered Users 2 Posts: 19,106 ✭✭✭✭TestTransmission


    Littlehorny wrote: »
    As said before it is a much safer way of coming down an incline aswell.

    How exactly is it safer?


  • #6
    R.O.R
    Registered Users, Registered Users 2 Posts: 12,712 ✭✭✭✭R.O.R


    TestTransmission wrote: »
    How exactly is it safer?

    Littlehorny means being in gear rather than coasting in nuetral.


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  • #7
    Littlehorny
    Registered Users, Registered Users 2 Posts: 2,351 ✭✭✭Littlehorny


    R.O.R wrote: »
    Littlehorny means being in gear rather than coasting in nuetral.
    Thanks R.O.R, being in gear means the speed of the car is in control i.e your not free wheeling.


  • #8
    TestTransmission
    Registered Users, Registered Users 2 Posts: 19,106 ✭✭✭✭TestTransmission


    R.O.R wrote: »
    Littlehorny means being in gear rather than coasting in nuetral.

    Ohhhh,ok.Totally misread that then.


  • #9
    Big Nasty
    Registered Users, Registered Users 2 Posts: 22,080 ✭✭✭✭Big Nasty


    If you're not pressing the accelerator you're not using any fuel.


  • #10
    Mr Benevolent
    Closed Accounts Posts: 12,456 ✭✭✭✭Mr Benevolent


    MCMLXXV wrote: »
    If you're not pressing the accelerator you're not using any fuel.

    Exactly, and it's another reason why slowing in 3rd is a feature of the driving test.


  • #11
    corktina
    Closed Accounts Posts: 17,733 ✭✭✭✭corktina


    If its a steep hill, you should be in a lower gear than 5th. It will retard your speed and that in the event of a brake failure would be of some assistance to you


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  • #12
    keithclancy
    Registered Users, Registered Users 2 Posts: 9,208 ✭✭✭keithclancy


    MCMLXXV wrote: »
    If you're not pressing the accelerator you're not using any fuel.

    And your Cruise Control isnt on ;)

    Otherwise you might be promoting a perpetual motion car.


  • #13
    Tallon
    Closed Accounts Posts: 22,565 ✭✭✭✭Tallon


    Turn off your engine, and then back on when you're at the bottom


  • #14
    [Deleted User]
    Posts: 23,339 ✭✭✭✭ [Deleted User]


    Confab wrote: »
    Exactly, and it's another reason why slowing in 3rd is a feature of the driving test.

    I don't know where you are after getting that nugget from. For your driving test whenever you are slowing you should have your foot on the brake. No doubt you should drop to third approaching roundabouts and junctions etc but you don't slow solely by downchanging.

    Regarding hills, you should do down a hill in the same gear you'd go up it in in urban areas (50kph limits), 5th down a hill isn't at all good practice unless it's a 100kph limit.


  • #15
    Mr Benevolent
    Closed Accounts Posts: 12,456 ✭✭✭✭Mr Benevolent


    RoverJames wrote: »
    I don't know where you are after getting that nugget from. For your driving test whenever you are slowing you should have your foot on the brake. No doubt you should drop to third approaching roundabouts and junctions etc but you don't slow solely by downchanging.

    I wash off about half my speed with downchanging and the other half with the brake and did the same in my test without any comment. Instructors never said a word either. I did fail the test, but not on that.


  • #16
    [Deleted User]
    Posts: 23,339 ✭✭✭✭ [Deleted User]


    ... your instructors should be telling you to always have your foot on the brake when slowing down to alert traffic behind you.


  • #17
    Dr_Colossus
    Registered Users, Registered Users 2 Posts: 3,191 ✭✭✭Dr_Colossus


    Tallon wrote: »
    Turn off your engine, and then back on when you're at the bottom

    lol, someone was on the radio a few months back who'd done just that, at the bottom of the hill was a bend which engaged his steering lock which then caused him to leave the road and into the ditch as the road straightened out again.


  • #18
    Alanstrainor
    Registered Users, Registered Users 2 Posts: 23,157 ✭✭✭✭Alanstrainor


    Dr_Colossus wrote: »
    lol, someone was on the radio a few months back who'd done just that, at the bottom of the hill was a bend which engaged his steering lock which then caused him to leave the road and into the ditch as the road straightened out again.

    I heard a story from a friend about that. Not too sure if it was the same story, but it resulted in a new car being written off! Shocking carryon!


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