Economical driving styles?
Posted by: Top Cat on 05 May 2005
Hi folks.
Have just borrowed an older 535i from my father, who doesn't use it very much. Taxed, insured, and thirsty. Just looking for tips for minimising the fuel consumption as I averaged well under 20mpg over the first 100 miles, which is fine but I'd prefer to keep the visits to the pumps down (and hence cost). Mainly, however, I'm treating it as a bit of a challenge to see just how economical I can get the old girl to run. After all, I like a challenge...
What's more, there's a wee guage below the rev-counter which shows current fiel consumption - and if I'm not careful I find the dial shooting off to the right below 10mpg. Ouch!
A couple of questions:
I've been trying the 'keep the revs below 3000rpm at all times' trick, and easing right off on the accelerator wherever possible - and using as high a gear as early as I can. However, is there a 'happy rpm' figure in which the engine is operating at its most optimal? Sometimes I can get the revs down to 1100rpm in fifth gear, but I wonder if running so low is somehow counter-effective.
Next question is to do with hills. WHat's the best strategy? Build up speed on the straight and use less accelerator up the hill, or try to keep the accelerator constant and let the engine find its own speed (or lack of it, heh heh). The car is quite heavy so its apparent consumption is highest when going up hills almost regardless of the speed.
Trying to see how economically I can get this brute of a car to run has been quite illuminating thus far, and an exercise in restraint. Quite difficult compared to regular driving as well, as the temptation to put the foot down and hoof it along must be suppressed...
Any tips? (no get a bike/scooter/bicycle/walk stuff - of course they're options but not really the point, and recommending an alternative car is all fine and well, but my father has loaned me this car and so it's otherwise costing me nothing)
Ta,
Wannabe-Eco John
Posted on: 05 May 2005 by Stephen B
quote:
Sometimes I can get the revs down to 1100rpm in fifth gear, but I wonder if running so low is somehow counter-effective
I reckon it's ok as long as you don't labout the engine too much.
What concerns me most (and forgive me for stating the obvious) is that you might be tempted to concentrate more on that MPG gauge than on the road. Driving for economy is all well and good but watching other road users and keeping up with the traffic flow is more important.
But of course you knew that anyway so tell me to shut up.
Posted on: 05 May 2005 by Matthew T
Coast whenever possible, down hills, coming up to lights, when slowing down.
Drive between 50-60mph on the motorway (likely!)
Posted on: 05 May 2005 by Nime
I hope you didn't mean coast in neutrel Stephen?
The greatest savings are by reading the road well ahead and maintaining a much greater than average diatance between your bonnet and "their" bumper. Accelerate gently and slow down gently. Your inter-vehicle distance is your freedom to drive how you want instead of being dictated to by the traffic.
I doubt anyone would have the nerve to take away your braking distance while driving a big BMW. But if they do then let them go, ease off and recover your nice long road space behind the idiot.
The more you use the brakes the greater the fuel consumption. Because you have to put that speed back on to maintain the traffic flow. So you ease off to slow the car well in time for the lights and the back of the next queue. How many times do you see "them" accelerate to the lights and then emergency brake with the nose bouncing on the ground? Idiots.
Turn the engine off when stationary in long queues and at traffic lights.
Avoid labouring the engine. In theory you should use maxium torque RPM which is *not* the same as maximum power.
Use as high a gear as possible once you have *gently* gained your required speed. It used to be the thing to have overdrive ratio diffs in economy competitions. Minis with 3.1 and 2.9 diffs, despite their small engines, instead of 3.44 and 3.65 as standard.
Nime
Posted on: 05 May 2005 by andy c
quote:
Turn the engine off when stationary in long queues and at traffic lights.
I wouldn't do this as it could affect your ability to get away etc in the event of being caught out - and in any case re starting consumes a fair amount of fuel. As mentioned above better judgement of distance between you and the vehicle in front will make you much smoother (If you dont do this already of course).
Is it auto or manual?
andy c!
Posted on: 05 May 2005 by count.d
quote:
Coast whenever possible, down hills, coming up to lights, when slowing down
That's wrong. You should use the appropriate gears when slowing down. The engine doesn't use any fuel whilst deaccelerating. Whilst coasting in neutral, the engine is using fuel to keep the engine at tickover.
Engine efficiency is maximum when the max torque value is reached. The reason that economy (efficiency) maximizes at the torque peak is because this is the place where the engine is inhaling the greatest amount of fuel and air into the cylinder which, when burned, makes the peak amount of cylinder pressure and thus the maximum torque. This is all very well for a standing engine, but in a car the biggest effect on fuel economy is aerodynamic drag. So basically the slower you go the better the fuel economy.
P.S. Don't go too slow in each gear, as this will put too much stress on components.
Posted on: 05 May 2005 by Top Cat
quote:
Is it auto or manual?
It's manual - though most 535i's were auto. It's also been to the moon and back. The odometer reads 105k, though we have reason to suspect that it has been clocked prior to purchase at auction (and my father's bid reflected his suspicion). It's probably 200k+, but in terrific nick.
ANyway, thanks for the tips - keep 'em coming.
John
Posted on: 05 May 2005 by Bruce Woodhouse
The really serious way to reduce economy is to actually to drive right on the bumper of the car in front (or better still a lorry) and thereby get an aerodynamic advantage. This is called 'ghosting' I believe. Aerodynamic drag increases exponentially with speed if I recall, another reason why high speeds=more fuel.
Better to pay for more fuel I'd say!
Just check things like plugs/air filter are up to scratch, would make a difference if not.
Turn off the aircon, saps power (and therefore fuel) but keep the windows up or you get more drag!
Bruce
Posted on: 05 May 2005 by Martin Clark
Find out where in the rev range peak torque occurs and try to pick speed/gears to keep the engine near the torque peak. It's where volumetric efficiency is greatest - you get the most bang for the fuel expended, and will make progress with minimum of excess throttle opening.
The real answer is to fit a manifold vacuum guage (= turbo boost gauge) and use that to try to maintain as great a vacuum as possible.
Don't overlook the fact you may get better mileage on higher grade fuel, if the ECU can adapt to exploit greater ignition advance at cruise. The gains can offset the higher fuel cost - could be worth a tankful or two to see.
Using these two tricks I can squeeze 40-42mpg out of my saab (NG900SET, tweaked, pretty damn quick) on long journeys and turn in 32+ on long-term average - despite quite a bit of point+squirt
Posted on: 05 May 2005 by Stephen B
quote:
It's also been to the moon and back.
That'd be 476k+ then. Assuming you meant Earth's moon.
Posted on: 05 May 2005 by Top Cat
OK, just to the moon (once). Pedant!
John
Posted on: 05 May 2005 by JeremyD
1) Don't be mislead into believing that accelerating as slowly as possible is best: engines funtion most efficiently at constant RPM, so there is such a thing as accelerating too slowly. Accelerate fairly briskly without pressing the accelerator "too far" or letting the revs get "too high".
2) <Engines are typically most efficient at 3000-3500 RPM, so if you're driving in conditions where the engine load changes a lot, try to keep the revs in that band (or whatever is appropriate for your car) -oops, should have read all the other posts before posting this bit>. When going up hills you should accelerate before the hill starts, anyway, and it's best to go up at 3000 RPM in a lower gear than struggle along at 1500 RPM - the best way of judging is by how far you have to press the accelerator pedal for any length of time.
3) Obviously, on a flat motorway it's worth changing up to fifth when you know that you can stay there for a long time, even if the revs are low. If you find you're pressing the accelerator further than you were in fourth then obviously you should be in fourth...
Posted on: 05 May 2005 by Steve Toy
quote:
I hope you didn't mean coast in neutrel Stephen?
All BMWs, even the old ones come with a fuel cut off device for when you take your foot off the throttle.
Driving at 45 mph in 5th gear in 30 mph limit zones will help too.
Posted on: 05 May 2005 by Paul Ranson
Engines are more efficient the wider open the throttle is. There's some somewhat bogus advice up thread. The general rule is when you have to gain speed use big throttle openings and short shift.
IIRC most cars are set to be particularly efficient at 56mph in top, since this is one of the standard fuel consumption tests, so annoy everybody by driving at this speed. Then minimise your deviations from the average.
Paul
Posted on: 05 May 2005 by matthewr
Could you not just get a Nissan Micra?
Matthew
Posted on: 05 May 2005 by Derek Wright
My own set of biassed views
: accelerate briskly to cruising speed to minimise acceleration time (this based on study by a motor manufacturer some time in the 80s)
: minimise changing pressure on the accelerator - eg if the car has a stiff suspension then a far amount of low frequency vibration will be transmitted to the accelerater foot there by causing the foot to increase and decrease pressure on the accelerator causing the car to attempt to accelerate and then engine brake - if possible use cruise control to overcome the up down motion on the accelerator and to keep the speed constant.
Agree with leaving plenty of braking distance in front of the vehicle to mimise the need for braking and accelerating
Posted on: 05 May 2005 by Matt F
If it's got cruise control then you could use this on the motorway where possible. You should find this is more efficient (especially on inclines) and can check this on the economy gauge you mentioned.
Also - keep tyres pressures up to spec - low pressure = increased consumption.
Alternatively - what about an LPG conversion
Matt.
Posted on: 05 May 2005 by HTK
Just make sure it's in tip top health and drive normally. Stay under an indicated 80 on motorways (where conditions permit) and anticipate as best you can. People burn more fuel through not paying attention than by trying to save it. I cruised home this afternoon on the M3/A303 in no particular hurry but not slouching about in my 100k 528 (auto)at an average of 34.5mpg, probably averaging around 65mph. Driving around London on a hot summer day I get 12-18mpg. Horses for courses.
Have fun.
Posted on: 05 May 2005 by Nime
Are we certain about this "brisk acceleration" Jeremy?
I was taught that this guzzled fuel.
The so-called "leaden foot syndrome" was much warned against.
Early changing up without labouring the engine was always the order of the day.
Maintain speed without uneccessary braking.
Drive as smoothly as possible.
I drove a fibreglass sports car listening to the music of a big carb for ten years. I think I know how much fuel was guzzled when I accelerated hard and when I cruised gently up to speed. Even if the latter took rather longer.
Perhaps it's different with BMWs?
Here's some online advice I found for those worried by increased fuel prices.
http://news.carjunky.com/gas_saving_tips.shtmlNime
Posted on: 05 May 2005 by Tristram
The best way to ensure better fuel efficiency should include:
1) Regular scheduled tune up's and oil changes
2) Checking the oil and topping up periodically
3) Checking tire pressure regularly, which tends to change with temperature
4) Tires (summer and winter) will generate different fuel demands.
The comment to turn off the engine while idling is a poor one for 2 reasons. First it requires fuel and stress on components to restart the car, and Second it increases the emissions by lowering the the engine temperature.
BMW's come with an engine that is meant to be driven hard and at high rev's. Low rev driving (quickly changing gears on low revs) will add to the cost of driving by damaging the engine.
I can appreciate the concerns about fuel prices, but part of driving a car should be enjoyment. So take that car out, drive the hell out of it, and enjoy yourself.
tw
Posted on: 05 May 2005 by DAVOhorn
Over the years many things have been tried to improve fuel consumption.
1950's SAAB had the freewheel gearbox. So engine and gearbox disconnected on the overrun.
This equalled higher brake pad wear
1950,60,70, a variety of wheezes on tyre types to reduce rolling resistance thus increase economy. Reduced rolling resistance equalled less grip and poorer handling and braking.
1950,60,70,80, Aerodynamics came into being and resulted in more efficient designs to reduce aero dynamic drag.
Great exponents were Bristol,Panhard,Citroen,
Lotus,Porsche etc etc.
1980' onwards A variety of engine management systems to control the no of cylinders running.
Say a V8 anywhere between 8 and 4 cylinders running. Some cars shut down one bank of the V8.
1980- todate VW had engine management systems that shut off the engine when stationary and the engine would restart when acceleartor pressed.
Look to the 80's and AUDI VW research into intelligent systems to maximise efficient running at motorway speeds.
Still he best way to drive economically is at a constant speed on an empty motorway at about 55 mph.
Trouble is is that is not the real world.
A new one is the new tyre that has no air in it. It is a very stiff tyre with no side walls as such. But has readial transverse walls which provide a high stiffness to twisting and good bump absorption to vertical deflection. I have seen a photo and it is kind f weird looking.
regards David
Posted on: 06 May 2005 by Derek Wright
The SAAB free wheel system which was in the 95, 96 and early 99 models was great for teaching you to leave adequate braking distance from the vehicle in front.
In some automatic cars there is reduced engine braking below certain road speeds and in the higher gear ranges.
Posted on: 06 May 2005 by Top Cat
quote:
Could you not just get a Nissan Micra?
No. Say I bought a Micra for £2k, I'd have to do a heck of a lot more miles before the petrol savings liberated by using the Micra offset £2k cost - the BMW was/is free, after all.
I reckoned that, at 10p/mile for the Micra (estimate) and 26p/mile for the BMW (again, estimate) I'd have to put in more than 12.5k miles before regaining that two grand in petrol savings. Consider the BMW option the 'flat earth' option...
And I'd have to do all of those miles in a Nissan Micra. Yuk
John
Posted on: 06 May 2005 by Steve G
quote:
No. Say I bought a Micra for £2k, I'd have to do a heck of a lot more miles before the petrol savings liberated by using the Micra offset £2k cost - the BMW was/is free, after all.
Gordon Brown will be glad to hear that as a point of view, but the Green party might not be so keen...
Posted on: 06 May 2005 by Derek Wright
An argument for driving a smoke issueing clunker over buying a new small car is that by not buying a new car you are saving all the emissions and polution created when the new replacement car is made.
Speculation on - perhaps more pollution etc is created during the build of the car and it's components than is issued by the car driving around for the rest of it's life..
Speculation off
Posted on: 06 May 2005 by HTK
I don't know if you need to speculate on that. I thought there was a body of evidence, esp from Sweeden that running a properly serviced car over it's operational life caused less emmissions than building a new one. You'd have to take the knackered clunkers out of that equation.
