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Thread: Engine Braking

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    Engine Braking

    I recently heard that when you are engine breaking (ie, in gear but not applying any pressure on the throttle) the engine is using no fuel whatsoever. Is this correct? Apparently the ECU cuts the supply of fuel to the engine, even when decending down steep hills where your revs would climb (due to engine braking).

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    im not sure but i tend to drive like that alot so i hope so lol
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    Yes this is correct
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    Having recently read the Institute of Advanced Motorists handbook I saw something similar and thought that it couldn't be true.

    It said that with modern fuel injected engines when your foot is not on the throttle pedal the engine is not using fuel. Presumably it is using some fuel, otherwise it wouldn't be running, but maybe just enough to keep it ticking over?

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    No fuel is used, the engine stays running because the wheels are keeping it moving. Only if you put your foot on the clutch, or your engine revs begin to drop to stall speed is fuel used again.
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    So presumably the reason for current advice to coat to junctions but not put the car in neutral?

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    Spot on, putting the car in neutral and coasting will consume fuel to keep the engine going. Keeping in gear with no throttle consumes no fuel
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    according to the IAM handbook you should leave the car in whatever gear you are in on approach to the lights, apply the brakes and engage the clutch only at the moment the car is about to cut out.

    I went on a couple of lessons with the IAM instructor and, since the first lessaon, I've been adding about 100km to the range on a full tank just by using the simple tips like the one above. Previously I would have gone down through the gears when approaching a junction.

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    Quote Originally Posted by MarcQuinlivan
    according to the IAM handbook you should leave the car in whatever gear you are in on approach to the lights, apply the brakes and engage the clutch only at the moment the car is about to cut out.

    I went on a couple of lessons with the IAM instructor and, since the first lessaon, I've been adding about 100km to the range on a full tank just by using the simple tips like the one above. Previously I would have gone down through the gears when approaching a junction.
    I always find this interesting,as I have been driving more years than I care to remember,I have always used a combination of gearchanges/brakes when approaching traffic lights/roundabouts etc and had many a scary moment when trying to teach my offsprings the art of driving (many times have I "done" the braking for them,trying to do a fred flintstone)
    Not really commenting on the fuel saving by driving like this but my brakes and clutch tend to last longer and also when I get to the juction/roundabout I am in the right gear to proceed if it is clear as opposed to some who have to stop because they have approached in a high gear and used their brakes to stop then struggle to find the right gear to move off again.How many times have you nearly rear ended someone who has stopped for no apparent reason,at a roundabout, as the road is clear to proceed.

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    I've always used engine braking - feel more in control that way. Coasting to a halt in neutral just seems wrong. I've often wondered whether fuel was being used though but it makes sense that none is.

    Of course this could open up the whole engine vs brake wear debate but unless you're dropping down a cog and redlining then I don't see any issues.
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    Quote Originally Posted by haids
    I recently heard that when you are engine braking (ie, in gear but not applying any pressure on the throttle) the engine is using no fuel whatsoever. Is this correct? Apparently the ECU cuts the supply of fuel to the engine, even when decending down steep hills where your revs would climb (due to engine braking).
    The fuel is cutoff so long as the engine revs are above about 1400rpm.

    When I was taught to drive (in 1975) we were taught to use engine braking whenever possible - since it saves the brakes for when you really need them and saves fuel.
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    Quote Originally Posted by dipstic
    ...also when I get to the juction/roundabout I am in the right gear to proceed if it is clear as opposed to some who have to stop because they have approached in a high gear and used their brakes to stop then struggle to find the right gear to move off again.How many times have you nearly rear ended someone who has stopped for no apparent reason,at a roundabout, as the road is clear to proceed.
    Again, the IAM advise that an advanced motorist approaches a junction (stop sign, red lights, etc) as if they will have to stop. The car behind you approaching this type of junction should also be preparing to stop as there is a car ahead of them, so should be in no danger of running into the back of you.

    A roundabout or a junction marked with a yield sign do not require you to stop, so for these junctions you approach the junction driving normally, then when you have braked sufficiently, change down to an appropriate gear to negotiate the junction if clear, but be prepared to stop if necessary.

    I have to admit, braking towards the junction and then engaging the clutch just before the engine cuts out was a bit unnerving at first, but when you get used to it it does not seem strange.

  14. #13
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    Quote Originally Posted by MarcQuinlivan
    according to the IAM handbook you should leave the car in whatever gear you are in on approach to the lights, apply the brakes and engage the clutch only at the moment the car is about to cut out.

    I went on a couple of lessons with the IAM instructor and, since the first lessaon, I've been adding about 100km to the range on a full tank just by using the simple tips like the one above. Previously I would have gone down through the gears when approaching a junction.
    My old company paid for me to go out with a chap from IAM. Kind of promoting good driving skills etc.

    THe chap told me he would observe me first, then we'd pull over and discuss techniques. So i set off, and we cruised around for about half an hour. i thought "Ha, this is going well, nice steady cruise over the tops on a lovely day" i was convinced he'd pull over and tell me i was a natural.

    But no. LoL, the first thing he told me was how i changed through the gears instead of remaining in the current gear (even 6th) and braking to the point of cut out, only then dipping the clutch to engage the gear required next (even 1st at the light for example). It was a weird thing to get my head round at first but it does work! I too have enjoyed increased MPG.

    Also he slated my road positioning, but thats another story

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    Wow I always just stick it in neutral. Not anymore though... learn something new everyday =)

    Thanks!
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  16. #15
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    Quote Originally Posted by L60N
    THe chap told me he would observe me first, then we'd pull over and discuss techniques. So i set off, and we cruised around for about half an hour. i thought "Ha, this is going well, nice steady cruise over the tops on a lovely day" i was convinced he'd pull over and tell me i was a natural.
    I did the same, but after the first lesson he told me there was hardly anything wrong - just the braking to the junction and my hand positioning on the gearlever when changing gears were the major ones. At the end of the second lesson he reckoned I was ready to apply for the advanced test, and that by the time it came around I'd have all the minor things ironed out.

    Quote Originally Posted by L60N
    But no. LoL, the first thing he told me was how i changed through the gears instead of remaining in the current gear (even 6th) and braking to the point of cut out, only then dipping the clutch to engage the gear required next (even 1st at the light for example). It was a weird thing to get my head round at first but it does work! I too have enjoyed increased MPG.
    He said the preferred protocol at the lights after coming to a stop in whatever gear you are in is to engage the handbrake, then select neutral and release the clutch pedal. I asked why I wouldn't select first and leave the clutch in ready to set off and he said it adds unnecessary wear and tear. He also said that the purpose of the amber light before the green was to give you notice that the lights would be going green and have first gear engaged ready to go on green. The amber light is not a signal to bury the throttle.

    On a side note, I have to say the IAM tuition is well worth doing. I've noticed a drastic improvement, not only in fuel consumption, but also in my attitude to driving. Previoulsy if I was stuck behind someone going slower I'd be all over the back of them trying to get past, whereas now I'll hang back slightly to get a better view and be ready to pass when there's enough room. I find I arrive at my destination so much more relaxed and no later than I would previously have done.

  17. #16
    I always find this interesting,as I have been driving more years than I care to remember,I have always used a combination of gearchanges/brakes when approaching traffic lights/roundabouts etc and had many a scary moment when trying to teach my offsprings the art of driving (many times have I "done" the braking for them,trying to do a fred flintstone)
    Not really commenting on the fuel saving by driving like this but my brakes and clutch tend to last longer and also when I get to the juction/roundabout I am in the right gear to proceed if it is clear as opposed to some who have to stop because they have approached in a high gear and used their brakes to stop then struggle to find the right gear to move off again.How many times have you nearly rear ended someone who has stopped for no apparent reason,at a roundabout, as the road is clear to proceed.
    I'm the same. I was taught to drive by a Police advanced driving instructor and he also said the most important thing about driving apart from observation was to always be in the right place in the correct gear for any given situation.

    Although I have a DSG gearbox I always drive in tip-tronic mode and change down to the gear I need to exit as roundabout as I approach. Obviously if I do have to actually stop the DSG automatically selects 1st anyway. As you say so many drivers seem to end up at a roundabout in totally the wrong gear and 'dither' trying to get going again when it's clear. Putting the car in to neutral as you apparoach is no a good idea as to have very little control over the car whilst it's in neutral.
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    Quote Originally Posted by MarcQuinlivan
    Again, the IAM advise that an advanced motorist approaches a junction (stop sign, red lights, etc) as if they will have to stop. The car behind you approaching this type of junction should also be preparing to stop as there is a car ahead of them, so should be in no danger of running into the back of you.

    A roundabout or a junction marked with a yield sign do not require you to stop, so for these junctions you approach the junction driving normally, then when you have braked sufficiently, change down to an appropriate gear to negotiate the junction if clear, but be prepared to stop if necessary.

    I have to admit, braking towards the junction and then engaging the clutch just before the engine cuts out was a bit unnerving at first, but when you get used to it it does not seem strange.
    Well touch wood I have never rear ended anyone yet both my offsprings have since passed their tests (basically ended up just giving them on road time, as my driving seems to be so outdated compared to what seems to be taught nowadays)
    Still think this braking lark is to save having to teach the pupil all about gear selection/engine revs , how many could change up and down without using the clutch (and not have an auto)

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    Quote Originally Posted by consilio
    Spot on, putting the car in neutral and coasting will consume fuel to keep the engine going. Keeping in gear with no throttle consumes no fuel
    But surely if you are going up a hill in gear with no throttle in first it will pull you up then surely you are using fuel

  20. #19
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    If you are doing around 5-10mph then yes, because its near the minimum revs that the engine requires to stay running, it will use fuel to keep the car going. If you are in gear, it will of course move the car as well.
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    Here is a rather interesting article about a guy who does something called hypermiling, which seems to involve a lot of driving without using the brakes at all, and slipstreaming behind trucks with the engine turned off. He returns 59mpg from a standard petrol Honda Accord.

    He also got 180.91mpg out of a Honda Insight (whatever that is!) using the same method.

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    Quote Originally Posted by MarcQuinlivan
    The amber light is not a signal to bury the throttle.
    .
    LOL!! like reaction times on a drag strip!

    One thing I've noted, I've always found that's juuuust about the right time to nail it in my DSG, the take up "slack" means you're running just when it hits green and you make a proper get away

    Dave, like you I use "manual" mode all the time, with the exception of really slow moving traffic, clicking down just before roundabouts etc, my wife also does the same - I wonder how many mostly people use D in the DSG

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    One reason for not changing down through the gears as you slow down is that clutches are more expensive to replace than brakes.
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    after ignition, the engine will try to maintain at least 800 or so rpm
    when you are in gear, just as the engine can drive the wheels, the wheels can in turn drive the engine; they are directly linked.
    if momentum is keeping the car rolling, the wheels will turn the engine over and as long as you arent dropping below whatever the engine idle speed is, no fuel will be pumped in as long as you stay off the throttle.
    this is true even in automatics...

    for "proof", get on a road and coast in gear... look at your fuel consumption... then stomp on the clutch and watch as the fuel consumption actually becomes *not* zero as the engine now has to turn over at idle rpm using its own power rather than momentum

    when you need to slow down/stop, stay in whatever gear and stomp on the clutch not "just as its about to cut out", but a bit before... ie. don't do it when your revs have dropped to 600 and the engine is really choking.

    predict the road conditions as you slow down, rev-match down-shift into whatever gear you are likely to need just before you reach the point where you need to accelerate again.

    whilst engine braking, especially if there is poor visibility and there are cars behind you, make sure you actually use your foot brake too. you need to have that brake light on as you are slowing down.

    also remember, always expect the worst from other drivers. no matter how much an accident is not your fault and you have insurance, its always a royal pain in the ass.

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    Quote Originally Posted by MarcQuinlivan
    Here is a rather interesting article about a guy who does something called hypermiling, which seems to involve a lot of driving without using the brakes at all, and slipstreaming behind trucks with the engine turned off. He returns 59mpg from a standard petrol Honda Accord.

    He also got 180.91mpg out of a Honda Insight (whatever that is!) using the same method.
    saves petrol maybe, but im sure he spends more on other parts... like rubber
    "Drafting 18-wheelers with the engine off, taking death turns at 52 miles an hour, and other lessons learned while riding shotgun with the king of the hypermilers"

  26. #25
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    Well for me it depends if I am lazy I put in neutral when going slowly and brake to a stop gently... otherwise I go through gears...

    when any gear is engaged I always make sure RPM is never less than 1000-1200, otherwise I change down (OK first gear is different...) Because lower RPM to the point of the combustion is not good )engine almost dying on you) puts so much pressure on the conrods (hidraulic pressure of unburnt fuel) that is really not good for engine life...

    In doubt give it more revs, engine will appreciate it... believe me!

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    [whilst engine braking, especially if there is poor visibility and there are cars behind you, make sure you actually use your foot brake too. you need to have that brake light on as you are slowing down.]

    Above statement explains all the rear enders on motorways then.
    I dont need to worry about the car in front stopping/slowing untill I see his brake lights on

    And yes I know what you mean so the queue in the outside lane on the motorway all driving a foot away from one another are all hoping that
    a) Everyones brake lights work
    b) No one is driving on the throttle/engine braking

 

 

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