Conference terri::cars_uk

    
    
    
    
    I have found that if you lift your foot from the floor boards
    that this does occaisionally improve fuel economy, but its
    only marginal and hardly worth the effort... ;-)
    
    To look at the more serious problem of getting home on the fuel
    you have available. I know it can be very worrying to watch the
    gauge descending toward the empty mark.
    
    My advice to you is, drive fast enough to get home before the gauge
    reaches the "E".

    
    
    ;-)

    	Nice reply Mr Jenkins! Taking tongue out of cheek for a moment, I
    have always wondered how folks get 100+mpg out of "standard" cars in
    economy runs. One thing to remember is that you ALWAYS use up fuel when
    you press the accelerator, no matter whether petrol/diesel or carb/fi.
    
    	Another interesting point is that the winning Jaguar at Le Mans
    (which was run by the Americal IMSA Jag team) ran different (lower) gear 
    ratios to the other Cats. This meant that they had to feather very
    slightly at the end of one straight and were revving the engine more
    throughout BUT theu claimed to have superior fuel comsumption overall
    (I know we are only talking 4.5mpg rather than 4.3mpg here!!) because
    they could drive through the corners with an open throttle rather than
    have to lift and accelerate.
    
    	I find I get markedly better consumption if I drive at 75 on the
    Mway rather than 80/85. I know that sounds obvious but I keep an
    accurate fuel log and can often relate a bad "tankful" to a high-speed
    blat back from Heathrow! 
    
    	I averaged 43.6mpg overall in 58,000 miles with my BX19RD estate
    over 2 years and get almost exactly the same out of my DTR turbo
    estate. I can only suggest that you also fill the tank each time (and,
    if possible, do not use commercial vehicle diesel pumps because they
    pump faster and froth more) and keep an accurate log of your miles and
    consumption each time. Then experiment! Good luck.
    
    Colin

.2�              do not use commercial vehicle diesel pumps because they
.2� pump faster and froth more)

    Colin,

    Perhaps you ought to buy your diesel from the VW dealer here. :-)
    There are two diesel pumps, one pump for cars and a *faster* pump
    for comm. vehicles. I use the *faster* pump because the froth sub-
    sides *A LOT* quicker than normal diesel froth. I only wish the
    fuel companies would make all diesel less frothy.

    Martin.
    

    > I can only suggest that you also fill the tank each time
    
    Well, of course the purists would say this is not a good way to
    maximise your mpg.  Ideally, you should only take on enough fuel to
    cover the journey you're about to make, like aircraft do.  I have seen
    suggestions to only half-fill the tank, which is a compromise.
    
    In any case *I* can't be bothered and fill up each time :-)
    
    Jeff.

If you only keep the tank half full, then there is more space for the fuel to
evaporate into, so more fuel evaporates and is lost to the atmosphere when you
take the filler cap off.

Keeping your tank full reduces losses due to evaporation, but also reduces MPG
as you're carrying more weight around.

So it probably doesn't make much difference to your MPG how full you keep the
tank...

Scott

    .-1 - must be joking !

The effect is quite noticeable in hot weather.  A very obvious "puff" of
escaping vapour as you remove the filler cap.

Unless your cap is loose of course, in which case you're losing even more
vapour...

Scott

    Serious you might be, but the amount of fuel lost in vapourisation is
    nowhere near the amount of extra fuel burnt in order to lug around 1/2
    tankful of unneeded weight.
    
    Jay

    
    
    That's also why I drive faster with a full tank. It helps me to
    get to the economical part of the tankful more quickly. ;-)
    

    If the weight you carry around is going to affect the mpg, I'd like
    to suggest to .0 "go on a diet!".
    
    
    
    Lose pounds overnight!

    
    
    Sleep with a pickpocket.

    

    Of course, the real fuel waster is the brake pedal. The accelerator
    uses fuel to obtain power, and there are plenty in this topic telling
    us how to use less by more careful use of it. But every time you
    brake, you are scrubbing off inertia which you have burnt valuable
    fuel to generate in the first place.
    
    So, along with all the good advice about gentle acceleration,
    anticipate the road so you can lose way naturally through the frictions
    in the drive train etc., and thus keep braking to the minimum
    necessary.
    
    Doesn't make the exciting screechy noises, tho.
    
    Steve

                              
    Well Colin (.2) as you are driving exactly the same car as me, if
    you pass this was again could you please spare a few moments to
    let me know your driving habits that achieve 43.6 mpg. 
    
    At what revs do you change up?
    What is your m-way curise speed (75?)
    What is you normal road cruise speed.
    What is you normal journey, m-way a-road urban (I think not)
    
    Shooting for 40mpg (thats saving �2.50 on petrol a DAY, over the astra)
    
    :J_still_on_his_first_tank_of_petrol

    This is a very interesting topic; in .0, you say you've just got
    a BX diesel turbo, and yet in .11, you say you're still on your
    first tank of petrol.
    
    I'd suggest a good way to same money is to use diesel fuel, as it
    is cheaper, and it's designed for your engine!!    :^)
    
    Now, to be serious, I've got a BX diesel turbo as well. (Did I
    mention I'm getting another..... ouch! OK back to the point.)
    
    I get 45 mpg if I drive very hard, and 50+ if I ease off a bit.
    I drive mainly on motorway and fast A roads; very little town or
    slow cross  country roads, so I don't do much accelleration/braking.
    
    I find that I change up at 4,000 rpm if I'm in a hurry, or 2,400
    if I'm not. (2,400 is really a bit low, as it drops the revs to
    1,600 or so, and the turbo isn't really spinning - but if I'm not
    in a hurry, I don't mind.) In my car, the acceleration slows down
    at 4,200+, before the rev-limiter cut's in at about  4,700.
    
    That might just be my car; I've driven another one that pulled very
    smoothly up to the cutoff.
    
    My caris the hatch, which is more aerodynamic (and so more economical)
    than the estate.
    
    How big is the tank? If it's 14.5 gallon, you'll find that you
    can do 600+ miles easily before a re-fill, and you'll find it difficult
    to drive in a specific testing manner for that long.
    
    The worst i ever got from my car was for continental driving, where
    I travelled at 110+ for long distances; it dropped to about 37 mpg
    or so. I reckon you'll easily attain 40+, unless you spend a lot
    of time in town traffic.
    
    but as a couple back said; just experiment, and adjust your driving
    style, until you're happy with the results.
    
    Peter.
    

    
    Ok as I'm on first tank of DIESEL will you forgive the little slip
    about petrol.  I will experiment and keep and log. I did this with
    the Astra, but I can tell you it made no little diffeerence wheather
    I did 70 or 85 squealled the tyres or drove like a fiesta.
    
    Thanks so far
    
    :J

    The best economy I have ever had was last Christmas between here and
    Calais travelling at about 120 kph. Since I've had the car (309 GRD)
    I wanted to get the `mpg' into the 60's. Well, I attained it! 62.5
    mpg to be precise. I was well chuffed.

    Martin.

    	I suggested filling up your tank every fill because otherwise how
    to you keep an accurate check of your fuel consumption??? You can
    certainly put half-tanls in for a period of time but you cannot then
    accurately relate the amount of fuel you put in with the miles you have
    travelled. Filling the tank creates an established reference point.
    
    	I do around 500 miles per tankful (it does 100 miles before the
    guage even moves on the DTR, then another 100 for each "quarter" on the
    guage. As Peter noted, the gearing and better aerodynamics of the hatch
    allow for better fuel consumption than the estate.
    
    	If I am tootling, I change up at about 3500 in 1st and 2nd in order
    to keep the revs up above 2000 (unless I am REALLY tootling) then about
    3000 in 3rd and 2500 in 4th. I cruise at 60/65 on my bit of back road
    and generally 75-80 on the M4. 
    
    	If I am in a hurry then I find "my" turbo wategate opens up around
    4300 and so changing up around the 4000 mark prevents it dumping the
    power. This is only really a problem in 1st and 2nd though as I find
    the acceleration quite adequate from about 2500 not to require revving
    it "all the way" to 4000 in every gear.
    
    	My 43.6 was achieved in the 19RD estate ; last year I covered
    nearly 24,000 in the turbo and got 42.58 overall. This year Jan - June
    I covered 10,600 miles at an average of 43.6 (that's a coincidence -
    I've just worked it out) with a best tankful of 50 mpg.
    
    	So, if you want economy, change up as early as possible without
    dropping below 2000, don't allow the hot hatches to embroil you in a
    dice and, most importantly, keep your Mway cruising speed to at or
    below 3000 rpm (80 mph).
    
    Colin

    I've gone thru' the entire note and nothing's mentioned about the spare
    tyre in the boot. If we leave it at home, it will definitely save you
    lots of gas. By the way, how often do we have a puncture?
    
    Just my 2 cts worth.
    
    Mike

     re.17 Interesting point.  It seems that a lot of drivers are extending this
    principle and leaving their brains at home when they go out.
    
    Mikef

    I keep a log of fuel for my Citroen diesel estate (BX19TGD).  She has 
    averaged 54.39 mpg over the first 3500 miles.
    
    At around 70mph she seems to return about 50mpg, reducing to about
    44mpg at 90mph.
    
    I love the financial effect of the car's fuel consumption, but it's at
    the cost of performance.
    
    Greg.

                     <<< Note 1131.19 by MALLET::MARTIN >>>

>    I keep a log of fuel for my Citroen diesel estate (BX19TGD).  She has 
>    averaged 54.39 mpg over the first 3500 miles.
    
    
>    I love the financial effect of the car's fuel consumption, but it's at
>    the cost of performance.
    
Try the TZD or TGD Turbo diesel?


lots more performance for little impact on fuel comsumption
(more details when I get my TZD TD in two weeks time!)

    That's good consumption Greg. I could get up into the high 40s
    occasionally with my old 19RD estate but averaged 43.6mpg overall. A
    lot of my mileage is motorway (cruising around 75-80). My current DTR
    turbo estate averages about 43mpg, too (best tankful is 50mpg) with, as
    suggested in the last note, much better performance on tap when you
    want it (like overtaking).
    
    Colin

    Well, I am surprised, When I ordered my Renault 19 Chamade GTD all
    I seemed to hear was how out dated the engine was compared with
    the Citroen/Peugeots but reading this note has restored my faith.
    I've had 46+ mpg average over the first 11500 miles with a 70/30
    split of motorway (75-85) and town/jam driving. Best was 55 mpg
    touring around Denmark perhaps it's something in their fuel!!
    Admittedly the "performance" doesn't compare to my old Orion 1.6
    but it's better than my wife's new Golf 1.3.

    As for economic driving I'd recommend taking your wife along :-)
    or more seriously work at identifying stress inducing facets of
    your driving and consciously avoiding them... turn the other cheek
    when someone cuts you up... scream at him not up onto his tail.

    	Ian.

    
    Well Ive had the BX(17TGD) couple of months now and can report
    
    criuse of 3000rpm (83mph) gives aroung 44mpg (m-way)
    83mph with a hang glider and family gives 40mpg (m-way)
    A/B road driving at around 40-70 (ie depends on the traffic) with hang
    glider on the roof gave 56mph !
    
    When the RED fuel light comes on I have got a 10 litres left ie a 160
    miles or two hours! driving, (I really need a double red warning
    light)
    
    Ok so not brillant, but realistic.  I love to have one of those fuel
    computers that are on some cars, so I could see the effects of my
    driving!
    
    :J
                                                          

    The press reports that the AA is now doing in independant survey of
    cars (65 per year) to give a second opinion of manufactures. The tests
    are not computer simulations (sic),  as per manufacturers' tests, but
    include:- * 6 mile surban run simulation shopping or school run;		
    * a gentle 20-mile drive (incl cold start);	* hard driving in heavy
    traffic; * motorway cruising; * 'brisk' cross-country driving.
    
    Summary seems to all cars are more fuel-efficient when driven gently
    (no surprise), and that diesels being more fuel-efficient from
    cold-start, are especially econimical for short-trip motorists. 
    
    Attached is table  (Source: Dail Mail, Thursday Nov 15th 1990.)
    
    
    MAKE/MODEL			OVERALL 	SURBURBAN 	GENTLE 
    *PETROL*			MPG 		DRIVING	 	DRIVING
    
    Citroen AX11 5sp		47.5		38.0		55.0
    Fiat Uni 45s		47.5		38.0		56.5
    Fiat Panda 750L		47.5		39.0		57.0
    Nissan Micra 1.2		47.5		40.5		57.0
    Daihatsu Charade 1.0CX	47.0		37.5		59.5		
    Fiat Uno 60S		46.0		37.0		53.0
    Ford Escort 1.3 4sp		43.0		36.0		50.5
    Ford Escort 1.3 5sp		44.5		36.3		52.0
    Honda Civic 1.3DX		42.5		34.0		51.5
    Vauxhall Astra 1.4/1.6	42.5		34.0		51.0
    Vauxhall Cavalier 1.6	40.0		30.5		47.5
    Toyata Carina 1.6XL/GL	38.5		28.5		45.0
    Audi 80 1.8			38.0		29.5		44.0
    
    MAKE/MODEL			OVERALL 	SURBURBAN 	GENTLE 
    *DIESEL*			MPG 		DRIVING	 	DRIVING
    
    Citroen AX14DTR		60.0		56.0		73.0
    Vauxhall Nova 1.5TD		58.5		54.0		73.0
    Vauxhall Astra 1.7D		57.5		49.0		70.0
    Ford Orion 1.8d (1989)	56.0		47.5		67.5
    VW Golf Turbo D/Umwelt	54.0		49.0		67.5
    Rover Montego 2.0D Turbo	53.0		45.0		63.5
    VW Passat CL TD		51.0		43.0		62.5
    Citroen BX19RD		47.0		44.0		54.5
    Peugot 405GT DT		47.0		43.0		58.0
    
    

    
    	Hi all
    
    			Should there be a noticable difference between fuel
    consumption when using unleaded compared to leaded.I filled my car up
    with unleaded and got about 180miles on a 10pounds.But now i've got
    leaded in for a change,and i've done 72miles and have only a quarter of
    a tank left.
    
    
    			Is this just a carboretter set up?or is this
    something I will just have to live with?
    
    	Andy.
    

    Are you saying your getting more or less MPG with leaded????
    How much is quarter of a tank??
    what car is it???
    
    Regards Martin

    
    RE.26
    
    >>Are you saying your getting more or less MPG with leaded???
    
    I'm getting much less MPG with leaded.
    	
    >>How much is a quarter of a tank.
    
    I've got a 11.4 Gallon tank so a quarter is about 2.9 gallons
    
    >>What car is it?
    
    It's an Astra 1.6 SR with standard carboretter (Varajet II)
    
    	Sorry for being so vague.
    
    		Andy....
    
    

    You have to watch what you say round here Andy or you get your head 
    bitten off ;-)
    
    With regard your question, it should be the other way round.
    I know of someone with a pug 1.6 gti that _should_ run ok on unleaded
    but never did. He changed to leaded and found that it ran much better
    and was more economical which off set the increased cost of 4 star.
    
    But hey, whats the big deal ? If it runs ok on unleaded, is clearly
    more economical and better for the environment, why do you want to
    run it on 4 star ????
    
    Roy

    
    	I occasionally run it on leaded for two reasons.
    
    	1)Because running it on unleaded permenantly does your engine no
    favours.So I use one leaded to every three unleaded.
    
    	2)With unleaded I find that after driving a few miles and then
    stopping my car tends to idle at slightly higher than usual,and so when
    I switch the engine off I occasionally get a small burst of
    pre-ignition.(The engine wants to start up again).But with leaded this
    occurs less often.
    
    
    	Any ideas.
    
    		Andy.
    

    Unleaded petrol is usually less economical in MPG terms than leaded.
    
    The pre-ignition is caused by the fact that unleaded does not contain
    the lead required to lubricate the upper cylinder of 'older' engines.
    It is therefore hotter, sufficiently hot to cause spontaneous ignition
    of the fuel/air mixture.
    
    Personally, I'd stick to 4-star, and soon.
    
    Laurie.

    
    RE.30
    
    	>>to lubricate the upper cylinder of 'older'engines.
    
    What do you class as an 'older' engine.My car is a 1987 SR,the last
    year that the SR was manufactured.I got in contact with the previous
    owner and she told me that she'd had the car specially set up to run on
    unleaded,I found this out after a few weeks,in this time i'd been using 
    leaded petrol.Do you think in the 2-3 weels that i'd been running it on
    leaded instead of unleaded,as the previous owner had used for 2 years
    was enough to warrant a carbon build up or some other problem.
    
    
    	Regards  Andy.....
    

    Quite frankly, in my opinion, any engine that wasn't specifically
    designed to run with unleaded, with the exception of thos physically
    converted, such as the new heads available for the 'A' series, should
    be left on leaded. As far as I'm aware, your Astra SR falls into that
    camp.
    
    This whole business of unleaded petrol is a huge farce, and many
    people, including European governments have been conned. In my opinion,
    Ford got it right, and a lean-burn, highly efficient leaded engine
    produces less harmful gases than an unleaded with a cat. With that in
    mind, personally, I wouldn't risk ruining an engine in the search for
    the mythical "green factor".
    
    Laurie.

    
    re: .30
    
    Also normal unleaded has a lower octane rating (that's what the lead
    was put in petrol for originally), so that it is more prone to
    pre-ignition, which means that the ignition timing must be retarded
    which reduces thermal efficiency, making the engine use more fuel
    for the same power output. This [proneness to pre-ignition] will also
    partially account for increased "running on". The effect might be
    reduced by using 'super unleaded', which has a higher octane rating.
    
    Mike H.
    

    
    	Excuse me for being thick,but if unleaded is less effcient then
    why does my fuel economy seem to be better for unleaded.Is it just
    the fact that i've only used one lot of leaded and with time the
    consumption will return to usual?or is my idle mixture/any other carb
    adjustment out?
    
    	Regards.
    				Andy
    	

>>    Quite frankly, in my opinion, any engine that wasn't specifically
>>    designed to run with unleaded, with the exception of thos physically
>>    converted, such as the new heads available for the 'A' series, should
>>    be left on leaded. As far as I'm aware, your Astra SR falls into that
    
    As you point out, this is 'your opinion'.  It is also mine.
    
    If the engine runs-on when using unleaded, that is proof that it is
    not *happy* with that particular diet.  Don't wait for the damage.
    
    The 'conversion' that the previous owner had done was probably just
    a change to the ignition timing.  A subsequent service may have changed
    this back to the original setting again...
    
    In my view, if a manufacturer states that a vehicle needs 1-in-'n'
    tanks full of leaded fuel, then it shows that the engine is not
    properly suited to unleaded operation.  Their comment will be that
    this amount of leaded petrol will avoid valve seat damage, etc.
    Of course, to use this fuel, you often need to retard the timing.
    This can lead to worse mpg/power output in the mean time.
    So, overall, there may be very little gain - in money/mpg/environment
    issues since you may use more fuel in this inefficient setup.
    
    J.R.

    
    Andy,
       can I/we assume that when you put petrol in your car you buy it by
    the � and not the litre ??, if so, with leaded petrol being some 20+
    pence (according the sign at the garage) cheaper then you probably
    started your economy measurement with 10% less fuel....
    
    If you'd really like to run an engine on unleaded then buy a Kawasaki,
    all their engines have, since 1978, been built to be used with unleaded
    fuel (and leaded throttle hand)
    
    Alan.
    

    Since Sept 91 I am working almost full time on a project at a customer
    site located approx. 180km from Valbonne. Going there twice a week
    means that I logged approx. 1000km per week for the last 6 months.
    I am filling the Venturi with 1 leaded every 5 unleaded. We only have
    98RON/88MON over here as unleaded and I have been doing the following
    observations:
     
    - mpg shows better with unleaded than leaded (5-10% improvement)
    - engine works better with unleaded
    
    The better mpg may come from point 2 ie I don't need to pull hard on
    the engine when running on unleaded.            
    
    I should point out that the Venturi engine is managed by a truly
    sophisticated computerized system. As an example it does all timing
    computations for ignition in real time for each spark plug based on a  
    bunch of parameters such as knock, inlet air temp & press, exhaust temp, 
    coolant temp, oil temp, exhaust CO/CO2 mix, ... It clearly makes a
    better use of the unleaded version.  

    
    A question on fuel economy.
    
    Is it more economical to slow down using the break pedal, dumping
    kinetic energy through the brake pads, or is it better to use engine
    breaking, ie. changing down through the gears ??
    
    Thanks in advance
    
    Ian.
    
    

A few things to look at - which is easier and cheaper to replace,
brake pads or clutch discs?  For the best fuel economy, as soon as
you see that you'll need to slow down, slip it out of gear and
slow down with the brakes.  Normal practice is probably to just
apply the brakes until the engine approaches idle speed (1000 rpm
or so) and then throw in the clutch.

Downshifting to a stop is fun, but puts extra wear on the clutch and
uses up more fuel, so it is not the econimical way to go.

Dave

    If your car is fairly modern and so has a fuel cut-off on overrun, and
    it is in a low enough gear for the cut-off to cut-off, then it is more
    economical to brake by using the gears.  
    
    I can get 99.9 mpg by doing this (according to the 3 digit fuel
    computer).  The important bit is getting a low enough gear.  I can use
    5th to slow down but at slow speeds/low revs it ONLY goes to 70 or 80
    mpg so the fuel hasn't been totally cut off.  This is all on an Astra. 
    
    I noticed a similar thing on a Citroen CX Athena, when the fuel computer
    worked, many years ago and changed my driving style.  Now when I slow
    down I think, "I'm paying for the petrol and someone else is paying for
    worn out gears/clutch/engine etc" so I use the gears to slow down.
    
    tp     

On fuel economy alone, i would guess that this depends on whether your
engine has automatic fuel cut-off or not.

There are other things to bear in mind though, like cost of brake pads
versus wear on the engine, car control, letting the guy behind know that
you are slowing etc.

I personally use engine braking IN THE CURRENT GEAR to slow down by small
amounts, but braking for more vigorous stopping. I don't change down a
gear to slow down, although i may change down to help maintain the same
speed when going down a hill.

Its is not a simple answer!

mb

    .39�A few things to look at - which is easier and cheaper to replace,
    .39�brake pads or clutch discs?  For the best fuel economy, as soon as
    .39�you see that you'll need to slow down, slip it out of gear and
    .39�slow down with the brakes.  Normal practice is probably to just
    
    I fully agree. This approach combines fuel and engine parts and
    manpower savings.

    But slipping out of gear before braking is either illegal or at best
    potentially unsafe, as you're not in full control of the car.
    (I believe you'd get failed for it in the UK driving test).
    
    john

>    Is it more economical to slow down using the break pedal, dumping
>    kinetic energy through the brake pads, or is it better to use engine
>    breaking, ie. changing down through the gears ??
    
Dunno about economy, but I find I usually need to use a combination of the
brake pedal, engine braking and the handbrake to stop...  :)
    
Chris.

>
>    But slipping out of gear before braking is either illegal or at best
>    potentially unsafe, as you're not in full control of the car.
>    (I believe you'd get failed for it in the UK driving test).
>    

nah you'd just get a ticking off :-)

I passed even with my coast round corners - gimme an automatic - "style" of
driving!

However I think I was just lucky as it is wrong to coast - not in proper
control etc...

	Paul.

    
    I believe that most modern fuel injections have a fuel cut-off so that
    if the engine is doing more than say 1500 revs but the throttle is
    closed ie. engine braking/over-run call it what you will, the fuel
    supply is cut altogether to improve fuel consumption, therefore the
    most economical is to start slowing early by coming off the throttle,
    but at steady revs rather than harsh engine braking thus all kinetic
    energy is dumped to the engine and keeps the fuel shut off completely,
    the best situation during slowing down would be to have the throttle
    closed and the engine doing 1500-2000 revs as long as possible, thus
    keeping the fuel shut off as long as possible. A Police driving
    instructor would tell you that you only need brakes for unforeseen 
    circumstances, and to actually stop from a gentle roll.
    
    Richard

    
    The only trouble I have found with having fuel cut off on over run is
    that it makes the ride very jerky.
    I had a super chip put into my engine management to stop the fuel cut
    off and smooth out thr ride. 
    
    ..Simon

Surely that only applies on early cars.

I have no problems with my Renault 19 in that respect, which, I suspect uses
this.

I think some management systems had problems at low revs.

Mark.