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Crusing in neutral is an offence, I recall many years ago a driver being prosecuted for travellin down Birdlip hill in Gloucestershire and having a road accident into the wall at the bottom. Add to that that if you use the brakes a couple of time in quick succession you run out of vacuum as the engine is at idle. I though it strange as the time because one of the old Saab's had a 'freewheel' in it's gearbox and that was sold in the UK. Regards Peter
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Crusing in neutral is an offence, I recall many years ago a driver being prosecuted for travellin down Birdlip hill in Gloucestershire and having a road accident into the wall at the bottom. Add to that that if you use the brakes a couple of time in quick succession you run out of vacuum as the engine is at idle. I though it strange as the time because one of the old Saab's had a 'freewheel' in it's gearbox and that was sold in the UK. Regards Peter
Hyundais have a system in place so if you're moving in neutral and apply the brakes the ECU detects this and applies a little throttle to keep the brakes going. Is this a common feature in other cars?
Shouldn't really be necessary though if you are driving properly...
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Some diesels have it as there is no vacuum, just a vacuum pump driven by the engine. Regards Peter
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>>Add to that that if you use the brakes a couple of time in quick succession you run out of vacuum as the engine is at idle
Apart from over-run, idle is where a petrol engine makes most vacuum - open the throttle, and the vacuum decreases - or, if you're an optimist, manifold absolute pressure increases with throttle opening!
Number_Cruncher
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And it's dangerous to coast anywhere -- no real control over the car.
The only time it's OK to coast down hills is if you're trickling down in a traffic jam at ~2mph.
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Have seen in various places best acceleration technique is 3/4 (I think) throttle and changing up just before 3000 rpm.
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I don't think downhill technique is actually a very significant part of maximising fuel economy anyway. In my view the factors are:
1) keeping the car in tip top tune, establishing by experience the period within which things start to go out of adjustment, and scheduling in preventative servicing.
2) anticipation and watching the road ahead. There is nothing inherently wasteful about using the throttle to build up speed.But every time you put your foot on the brake you are throwing away all the money you have just spent.
3) anticipating the gear you will need, whether higher or lower, in order to maintain a steady reasonable speed
4) being responsive to the engine's needs, and keeping it running as fast as possible but with minimum throttle opening. There is a speed in every gear at which the car feels as if it will drive itself. You are not forcing the pace, but neither letting it labour.
5) not being in too much of a hurry. If you want to cruise at 80, that's fine, but it isn't the best speed for fuel economy.
There are other factors, and they will vary in significance and point of impact from car to car, but that's my summary advice.
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> being responsive to the engine's needs, and keeping it running as fast as possible but with minimum throttle opening.
I thought that this was in fact inefficient. AFAIK an engine gets more efficient as it is more loaded, so a higher gear and lower RPM, even at a larger throttle opening, was more efficient?
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I think it's a matter of balance, between too fast and therefore ineficient, and too slow and slogging. Old stagers on the Mobil economy run (does that still happen?) used to labour their engines in high gear, but I suspect that was more appropriate for older design engines. In the end it comes down to individual sensitivity and experiment. It's possible over time to build up a picture of the fuel economy of your car under different circumstances.
I'm assuming for the sake of argument that fuel economy is the overriding issue. Obviously on occasions there will be others, like the need to meet deadlines, or not hold up other traffic.
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Smoothness is also a factor - try and imagine there's an egg (not hard boiled!) attached to each of the cars pedals, and you're trying not to break the eggs as you apply pressure to them.
S6 1SW
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And of course there is that old chauffeur's trick, of driving with a glass of water on the bonnet.
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Old saabs had overun gearboxs because even older saabs had a three cylinder two stoke engines where the oil was mixed with the fuel. With a closed throttle on overun very little oil would get into the engine causing damage hence the overun gearbox. The same gearbox was kept after saab replaced the engine with a ford V4.
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On my drive home last night I managed to average 51mpg on a 13 mile journey at 7pm. Traffic was light, roads consisted of town roads, country lanes, a dual carrigeway for around 8miles (at speeds of up to 70mph) and then back to town roads for a few miles. The car is a 1999 audi A4 1.8 with over 100k miles on the clock.
I am confident that without free wheeling I would have only got around 40mpg.
This is based on real world experience and I have been experimenting with this for about 2 years now. I notice that pretty much all of the other posts on this subject are only opinions so I thought it would be nice to have something based on facts :)
If anyone is interested I'm happy to elaborate further on my methods.
My personal best for this car was 52mpg.
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Sorry to upset you moonshine, but I guess the only way you measured the car's mpg was using the onboard compter gizmo. Relying on that is not too different from the opinions you mention. My A4 seems to do a tremendously good mpg using the computer but strangely when measured on a fill up to fill up basis it seems around 10% -12% worse.
I've been checking this for 30,000 miles so far and the difference seem consistent. Whenever I see the 50mpg or whatever on the dash I always deduct 10% and get depressed.
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With free wheeling, I think it works well in slow moving traffic.
But any faster, one must take into account the safety factor, and extra wear of the clutch, gearbox and brakes.
I think looking ahead, changing gears properly and driving at economical speeds is the best that can be done.
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Moonshine, I would appreciate if you could elaborate on the driving techniques you used to obtain your best economy figures.
Do you find it more economical to accelrate gently, or do you accelerate up to peak torque/rpm?
Have you found any difference in economy using different petrol brands?
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I'd be interested to know what these onboard fuel consumption meters work. Does it really incorporate two highly accurate flow sensors in the fuel lines ? (ie measuring the supply, and deducting the return) Or does it do some kind of estimate based on other parameters that it assumes broadly reflect fuel consumption?
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One major consideration on fuel economy if the correct inflation of the road tyres. Under inflated tyres cause significant fuel inefficiency.
Carse
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I've not seen any difference from different petrol brands. I use the cheapest I can get.
Yes, I used the onboard computer, it doesn't matter that it's not accurate just so long as it's reliably un-accurate. I'm only using it for comparison, so my point is still valid. it doesn't matter if it was 50mpg vs 40mpg or 45mpg vs 35mpg.
I dont see that it causes any extra wear on brakes, gearbox or clutch. My current disks and pads are fine after 50k miles.
it's all about getting the car up to speed and then avoiding using the brakes. Braking is a waste of energy.
I accelerate fairly briskly, change gear as soon as possible. If acelerating downhill you can get into 5th pretty quickly. Uphill you need to change a bit later. Try not to labour the engine. Never need to use much more than half throttle.
My view is that the two things that have the biggest impact are:
1 - Freewheeling (with the engine running!)
2 - Reading the road ahead to minimise the amount of braking.
Freewheeling - how can you say you don't have control of the car? Rubbish! You can brake and steer, if you need to go faster you just pop the car back in gear.
Freewheeling down steep hills - take the car out of gear before you start to go down the hill. Why not use the first part of the hill to pick up some speed. Try to get up as much speed as you can on the hill so that when you get to the bottom you can continue to coast for a while.
Freewheeling on the flat - pick up speed, freewheel, pick up speed, freewheel etc. This needs more explination but it does work.
Reading the road - be alert, be considerate. The freewheeling can mean that your speed changes from too slow to too fast. If you are in traffic this doesn't work so well. Aproaching traffic lights - think ahead, brake early if they are red, try to time it so that you are still moving when they go green.
In heavy traffic avoid this - stop -> acelerate quickly -> stop -> acelerate quickly
It's similar to the traffic lights, you want to keep moving. Try to get to the car in front just as they start moving. This will actually help those behind you as it smoothes the traffic flow and could even prevent accidents.
Some of these methods can't really be used when there is lots of traffic around as you need to keep with the flow. That's why I mentioned the time in the earlier post.
It's hard to explain in words exactly how I do it, you would really need
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lost a bit off the earlier post :
....you would really need to be in the car with me. Im sure others on this board will be able to explain better than me.
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I drive economically for fun now - getting as much mileage out of a tank becomes as much as a challenge as driving quickly to me (sad I know). I too allow the car to simply slow down when at all possible. I looked into the ways to drive economically after Audi (I think) told Clarkson to do it (let the car slow down) when he drove from London to Edinburgh and back on one tank of fuel on Top Gear a few years back. It seemed to work for him so I tried it and the results were positive ? so I?ve driven economically ever since.
I don?t trust my Leon TDi?s fuel calculator for the same reasons as the above post. So (sadly, again, I admit) I created an Excel spreadsheet to calculate my fuel consumption ? based on cost per litre (converted to gallons), total amount (£) to fill the tank, mileage per tank etc. I managed to get it to produce an accurate mpg rate for my car (and my missus? car). Before driving economically I was averaging 48mpg. Since concentrating on my driving technique I average 52mpg. For me, with the mileage I do, the results speak for themselves and I?ve driven that way ever since (especially as I claim the mileage back from work! ? the spreadsheet helps here too as it creates a record of my work mileage) I have not noticed my journey times increase at all but have noticed that I seem to make less mistakes and take less wrong turns (thinking ahead more I guess). Overall driving economically has been totally positive for me.
I would also point out that I have used the above spreadsheet to also measure the claimed benefits of BP Ultimate Diesel. I filled up with ten consecutive tank fulls (about 5k miles) and noticed?no discernable difference in mpg rates (on one occasion was 1mpg higher than average but fell again the next time). May obviously differ for other cars though.
These links give some general pointers which may help and I use most of the techniques mentioned (except for only half filling the tank):
www.iam.org.uk/pressroom/drivingtips/drivingtip16....m
www.iam.org.uk/pressroom/drivingtips/drivingtip18....m
As an aside, the spreadsheet actually helps ensure that the car(s) are working effectively. On one occasion my missus? car?s mpg dropped by 10mpg. After examining the likely causes I discovered the rear brakes had corroded and were catching slightly (she?d probably have never noticed despite me realising instantly once driving it). Because of the way (I believe) an on board mpg computer works, this may not have been picked up so soon.
Cheers
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>Freewheeling down steep hills - take the car out of gear before you start to go down the hill. Why not use the first part of the hill to pick up some speed. Try to get up as much speed as you can on the hill so that when you get to the bottom you can continue to coast for a while.
Freewheeling on the flat - pick up speed, freewheel, pick up speed, freewheel etc. This needs more explination but it does work.<
I don't like the idea of going down a hill in neutral - it feels unsafe. On top of that, if you were in gear, the car would not be idling and using fuel, but at higher revs with fuel supply cut off. Freewheeling on the flat as you suggest feels like it would make me sick!
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Diesels are very good in the 50-odd mph "busy but moving" motorway stuff. In my old Mondeo 1.8TD I just chuck it in top and it will maintain the speed with about 5mm of accelerator depression. There's virtually no engine braking either, so I can lift and maintain speed for a while as long as the road isn't heading uphill.
I was getting a chronically disappointing 37 mpg from this car when I first got it. Basically, I was driving it wrong - too many revs, boot down too hard, trying to accelerate quickly - all of which it despises with a passion.
Since I learned to use the torque and transfer some of the throttle pedal travel to the gearbox to keep it in its sweet spot, I'm now averaging 47 mpg from this old lump which is about 2 mpg more than its official combined figure. I try to keep the revs between 1,750 and 3,000 RPM where possible, which is where it seems to do its best work, let it gather speed at its own pace rather than welly it off the line, and generally accept it for the underpowered plodder that it is. It seems to yield good results.
Cheers
DP
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You've missed the point about coasting down a hill. Yes, the engine will be using petrol to maintain a tickover. However, this is offset by the fact that you pick up more speed and can then coast for further when you reach the bottom. This means you travel further before you need to start using the gas again.
If you have to stop at the bottom of the hill, say for a junction or traffic lights, then it would make sense to leave the car in gear.
Free wheeling on the flat is not as you think. Its all very gradual, with your speed going from say 60mph slowly down to 50mph and then slowly back up to 60mph again. It's surprising how long it takes for your speed to drop to 50mph.
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I've said this before, but in my hitchhiking youth, when HGVs were governed to 38 mph and there were no motorways, truck drivers used to freewheel down decent hills to shorten their journey times.
Once got a lift from a Tate&Lyle tanker and trailer that several times hit 70-odd going through the middle of small East Anglian towns, quite exciting. Couldn't help wondering what would happen if someone waddled into its path though. Would have taken a bit of stopping.
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