Motorway driving hints for fuel efficiency

shedweller

Another tehnique is to get up to your speed and then cast your eye towards the mpg meter, which should be on the instant readout for this. Note the reading then lift off the accelerator ever so slightly. Not enough to lose speed but to lower the instant reading. Done correctly and this will lower how much fuel is used at a constant speed.
I really can't explain how it works but it does. It does need very flat ground to work for any period of time though. But with practice i can get into this condition in a second or two.

Regarding the very slow acceleration. It was discussed at length somewhere and the consensus was that there is a too slow and a too fast rate of acceleration. So there's no need to piss off people with really slow acceleration either. There is a happy medium so experiment to find what suits your car.
I do feel like i need launch control sometimes as i take off from a set of lights. Really fast is just not enough for some people!

And yes, i could just drive her on but would add a fair few hundred euro to my yearly fuel bill. Not to mention new tyres sooner, new clutch sooner, new brakes sooner.....

SouperComputer

Zubeneschamali wrote: »

Slowing from my usual 125 kph to 85 kph would cost me 3 hours a week.

I think you have me confused with someone else. I'm not suggesting that you slow down to 85kph (i'll leave that to the idealists). In fact I never mentioned a specific speed at all bar my MPG example. If conditions are good and 125 is permissable, and especially if traffic is moving around 125 then drive 125. What I'm saying is whatever speed you you pick, just do it as efficiently as you can. Or not, its up to you

If I'm driving from St Paul to Chicago there's not fuppin way in hell im staying at 55MPH! It would add a huge amount of time to the journey.

opinion guy

LIGHTNING wrote: »

If your not on the brake pedal then you should be on the throttle pedal:)

lol.....whilst I might agree....its kind the wrong thread for that

SouperComputer

LIGHTNING wrote: »

If your not on the brake pedal then you should be on the throttle pedal:)

Or the handbrake :-o

shedweller

Zubeneschamali wrote: »

Slowing from my usual 125 kph to 85 kph would cost me 3 hours a week.

Thats about 18 minutes each way per 5 day week. Not ridiculous but i get your point. Maybe 90 to 100 would be better and still do ok on the mpg front?

Timmaay

SouperComputer wrote: »

Yes it makes a difference. You will use MORE fuel by popping it in neutral. The ECU tries to keep the engine running (naturally) so if you pop it into neutral it goes back to idle, requiring fuel. When you coast and leave it in gear becuase the engine is still operating above idle speed, theres no need for fuel, unless you call for it with the loud pedal.

FWIW I can get 29 US MPG (35 imperial MPG or 8.11L/100Km) with a twin turbo 2.8 if I'm deciplined enough to keep it at 55MPH. Once you get rolling its about aero and gradients moreso than anything else.

I take your point definitely but you can coast for far far longer by not having the car in gear.

Anyway, I usually fill up the tank, reset the trip counter and try vary my driving style but keep consist for the full tank, ie see how maybe coast as much as i can (safely) do for the full tank effects the mpgs, or keeping the revs low, or even rapid acceleration then driving gentle. Its interesting the changes that I get in fuel consumption, I drive a 2L civic, and get anything from 25mpg (on the vtec for a full tank driving the back roads) up to 40mpg with quite a lot of coasting.

For my normal weekly boring commute, doing 40mpg instead of about 32, the difference between driving in "eco" mode and just driving normally (but importantly my average speed is similar in both!) is about 90miles in distance, or approx 10L of petrol. That is a saving of 14 euros a tank (which lasts me about a week), not bad when you add it up over a year!

Big Nasty

SouperComputer wrote: »

You can change your car all you like, the biggest factors are road conditions and your driving habits. Unless you go to extremes. Its not exactly a bad idea to drive more efficiently, at the end of the day, what does it cost you? It barely even costs time if you do it right.

I don't want to change my car, nor my driving. The extent of my 'eco' driving is to occasionally give the throttle a little blip to change up a gear if, for example, I'm in second in traffic and feel I could manage in third. Otherwise I drive how I like and if I was that concerned about mpg I would buy a nice sensible diesel.

vectra

Just for curiosity I changed my driving style and route to see what difference it made

I normally travel the Fermoy bypass to Cork and back.@ 120kph "ish"

Travelling this route:
Week ending 21st Jan 2011 I used 45.25 L of Diesel to cover 712 Kms --Driving Normal
Giving me an average of 44.75 MPG


Last week I reverted back to using the B road
ie. Fermoy 50kph >80kph> Rathcormac 50kph>80kph> Watergrasshill 60kph> Glanmire Bypass 100kph >Cork

Same way on return

Travelling this route :
Week Ending 28th Jan 2011 used 37.47 to cover 694 Kms - Driving Conservatively
Giving me an Average of 57.20 MPG :eek:

Travelling the economy route it takes me approx 7~10 mins longer to reach my destination.
Not the end of the world but a good saving on fuel bill

SouperComputer

MCMLXXV wrote: »

I don't want to change my car, nor my driving.

Touche Nobody said you have to.

Vectra are you taking into account any changes in elevation?

nightster1

use dipethane additive in your tank, great for the engine and better mpg:)

Big Nasty

MCMLXXV wrote: »

Just drive her on FFS!

If you're that worried about consumption change your car.

SouperComputer wrote: »

You can change your car all you like, the biggest factors are road conditions and your driving habits. Unless you go to extremes. Its not exactly a bad idea to drive more efficiently, at the end of the day, what does it cost you? It barely even costs time if you do it right.

MCMLXXV wrote: »

I don't want to change my car, nor my driving. The extent of my 'eco' driving is to occasionally give the throttle a little blip to change up a gear if, for example, I'm in second in traffic and feel I could manage in third. Otherwise I drive how I like and if I was that concerned about mpg I would buy a nice sensible diesel.

SouperComputer wrote: »

Touche Nobody said you have to.

What are you talking about!?!

I never suggested changing my own car. I believe that if you are driving a car that you are constantly concerned about your MPG then you should change to a more 'suitable' car rather than driving it like a Granny to save fuel. I'm not concerned about my MPG, my first post was directed towards the OP!

dr.fuzzenstein

shedweller wrote: »

I believe the sweet spot for a small diesel lies around the 80 to 90kph mark. Below that and the mileage suffers, above that, it suffers too.
My last few tanks were in the 3.4 to 3.6 mark and that was with all the snow and ice driving. I do 95 to 100kph on the open road, paying attention to the throttle position on the downhill so as not to use any of as little as possible. But for the most time just driving.

Seriously, what do you drive?
Must be a very small car with a 1 litre turbo diesel, VW Lupo, five quid and left nut, nothing on earth could match those figures.
My Cmax will return just over 50 mpg when in a good mood and driven gently, the figures you quote are not possible on anything larger than a Polo.

pajo1981

peasant wrote: »

The most fuel efficient way to climb an incline is to build up speed on the flat, only feather the throttle on the climb and perhaps let speed fall off a bit just before the brow and let momentum carry you over.

It's completely the other way around peasant.

Building up enough momentum to carry you over the hill means incurring extra drag, which is lost energy basically.

Working directly against gravity (running the motor harder on the hill) is, by definition, a most efficient way to get you up the hill...

Doing what you described on the moon would also be as efficient.

zilog_jones

vectra wrote: »

Just for curiosity I changed my driving style and route to see what difference it made

I normally travel the Fermoy bypass to Cork and back.@ 120kph "ish"

Travelling this route:
Week ending 21st Jan 2011 I used 45.25 L of Diesel to cover 712 Kms --Driving Normal
Giving me an average of 44.75 MPG


Last week I reverted back to using the B road
ie. Fermoy 50kph >80kph> Rathcormac 50kph>80kph> Watergrasshill 60kph> Glanmire Bypass 100kph >Cork

Same way on return

Travelling this route :
Week Ending 28th Jan 2011 used 37.47 to cover 694 Kms - Driving Conservatively
Giving me an Average of 57.20 MPG :eek:

Try taking the motorway at 100 km/h and see what you get, or slower if you're willing to put up with impatient drivers. Having to slow down through the small towns doesn't sound great efficiency-wise, then again neither does having to slow down at the toll

I am starting to doubt myself about the whole engine braking = no fuel thing, I have seen conflicting information about it, though it may have been more relevent to older EFI systems (i.e. from before when cars all had fancy-pants trip computers ). Would be interesting to see fuel data straight from the ECU (I've seen people post graphs before, from a ScanGauge or something, can't remember where though), I'm sure trip computers are not the most accurate things around.

Victor Meldrew

peasant wrote: »

The most fuel efficient way to climb an incline is to build up speed on the flat, only feather the throttle on the climb and perhaps let speed fall off a bit just before the brow and let momentum carry you over.

This is all very like riding a bike, where you don't want to get sweaty, let momentum work for you.

Like the bit about the "sweet spot" cars have a natural equilibrium in each gear.

as with a bike and a boat in a swell , mometum is everything, and the harder you "work" for it, the better you'll hang on to it.

Timmaay

zilog_jones wrote: »

I am starting to doubt myself about the whole engine braking = no fuel thing, I have seen conflicting information about it, though it may have been more relevent to older EFI systems (i.e. from before when cars all had fancy-pants trip computers ). Would be interesting to see fuel data straight from the ECU (I've seen people post graphs before, from a ScanGauge or something, can't remember where though), I'm sure trip computers are not the most accurate things around.

The trouble with any sort of scangauges working through a normal OBD is the way they estimate fuel consumption. This is done by measuring the airflow into the engine (nearly every car has an airflow meter), and then by assuming that the fuel to air ratio is 14.7 (every 1 gram of fuel burnt, 14.7grams of air are burnt). You can work out the fuel flow, and sum up the fuel flow over the whole trip, and then divide by the trip distance for a MPG figure.

The two big issues with this are that A) for a diesel engine, you cannot relate the airflow to the fuel flow (diesel engines are not throttled, so will suck in more air at low revs then fuel) and , relating airflow to fuel flow does not take into account fuel shut off during engine braking.

Why don't we just use some sort of fuel flow meter you might ask!! Unfortunately most cars do not have one! From what I have seen the trip computer on a car uses some similar method to above.

In conclusion, The most accurate way to measure your fuel consumption still seems to be by measuring how long a full tank goes.

zilog_jones

Thanks for that, I didn't realise they generally don't have fuel flow meters, surprising in this day and age really considering nearly everything else has a sensor. That might explain what I saw in graphs so if it was based on air flow.

finnegan2010

Another bad habit some people have ie me is using the gears as a braking system. Coming to lights etc instead of engaging the brakes gradually. I use going down the gears from 4 - 3 - 2 to stop. I take it this eats fuel, as your increasing the revs? Might work out cheaper then replacing worn disk pads :rolleyes:?
Dont kill me i know feck all about cars

opinion guy

finnegan2010 wrote: »

Another bad habit some people have ie me is using the gears as a braking system. Coming to lights etc instead of engaging the brakes gradually. I use going down the gears from 4 - 3 - 2 to stop. I take it this eats fuel, as your increasing the revs? Might work out cheaper then replacing worn disk pads :rolleyes:?
Dont kill me i know feck all about cars

Oh dear god where is the Captain Picard facepalm link when you want it?


No engine braking as you do is the most efficient way to decelerate. The fact that the revs increase is nothing to do with using more fuel - you actually use less or no fuel doing this. The revs are caused by the kinetic energy of the car being absorbed by the engine thus slowing you down, using less fuel and sparing your brakes - hence the term engine braking.

opinion guy

nightster1 wrote: »

use dipethane additive in your tank, great for the engine and better mpg:)

Ok I've only recently heard of dipethane and know very little about it.

Any experts here who can enlighten me/us ?
Pros/cons ?
i.e. will my engine explode ?

Mr Benevolent

opinion guy wrote: »

Ok I've only recently heard of dipethane and know very little about it.

Any experts here who can enlighten me/us ?
Pros/cons ?
i.e. will my engine explode ?

Matt Simis is the man to know.

finnegan2010

opinion guy wrote: »

Oh dear god where is the Captain Picard facepalm link when you want it?

Here it is
http://www.acr0nym.com/gallery2/main.php?g2_itemId=1121


No engine braking as you do is the most efficient way to decelerate. The fact that the revs increase is nothing to do with using more fuel - you actually use less or no fuel doing this. The revs are caused by the kinetic energy of the car being absorbed by the engine thus slowing you down, using less fuel and sparing your brakes - hence the term engine braking.

he he he he

finnegan2010

opinion guy wrote: »

Ok I've only recently heard of dipethane and know very little about it.

Any experts here who can enlighten me/us ?
Pros/cons ?
i.e. will my engine explode ?

Will your engine explode? No
Will you waste about 20 squid buying it? Yes
Will the guy in the motors factors call you a donkey under his breath while he pockets your spondoolicks? Yes
Will your car all of a sudden increase MPG? Yes, in your imagination.


In fairness i bought it never noticed any change but then again Im some one to talk

http://www.acr0nym.com/gallery2/main.php?g2_itemId=1121

shedweller

dr.fuzzenstein wrote: »

Seriously, what do you drive?
Must be a very small car with a 1 litre turbo diesel, VW Lupo, five quid and left nut, nothing on earth could match those figures.
My Cmax will return just over 50 mpg when in a good mood and driven gently, the figures you quote are not possible on anything larger than a Polo.

1.4 diesel yaris. Here is a graph showing ALL my fuel used since i got it at the end of 2008:
I get up to 100kph and watch the throttle as best i can from there on. I use a block heater, grille block and tyres at 38psi. Even wear, tons of grip, no blowouts ever despite hitting the odd pothole.
It is possible, i do it every day and have no reason to lie

nightster1

opinion guy wrote: »

Ok I've only recently heard of dipethane and know very little about it.

Any experts here who can enlighten me/us ?
Pros/cons ?
i.e. will my engine explode ?

I'm no expert, but my mechanic is. I run a common rail 3.0 6 cyl diesel, before using dipethane, I replaced a number of injectors due to dodgy diesel. The injectors were replaced under warranty (€2K cost). The diesel fuel was analysed and found to contain some detergents and water. The garage refunded the dealer with the cost of the repair. Apparently, impure diesel is quite common around the country. That was 70,000 miles ago. I was advised to use dipethane. It lubricates and cleans the fuel system. Since then I have had no issues, I have better fuel consumption, little or no black exhaust smoke and passed 2 NCT's without any emission issues.


http://www.dipetane.com/

I'm sure that there are other equally as good fuel treatments but this stuff works for me.

Maruney

Im either calculating this wrong or my car is in great running order.
I spent €100 (@1.39.9/litre) last week so around 70 litres into my 73 litre tank. Thats around 15.40 gallons - Alfa 156 1.8 Sportivo

For that amount I got 605 miles on national roads and a little motorway driving.
High rise spoiler creating drag and I dont spare it much as lovely car to drive and handles very well but saying that it works out at over 40mpg which seems well over for this car, I was expecting 30mpg at most.

I do keep it in top condition and It is just back from the garage after full service, and front suspension rebuild so thay may help.

Marcin_diy

mickdw wrote: »

My cruise is not as efficient as myself for the following reasons:
It actually appplies brakes on decent to hold requested speed thereby wasting energy.

have you ever heard about engine breaking? your brakes won't move if you don't touch them.....

Marcin_diy

finnegan2010 wrote: »

Another bad habit some people have ie me is using the gears as a braking system. Coming to lights etc instead of engaging the brakes gradually. I use going down the gears from 4 - 3 - 2 to stop. I take it this eats fuel, as your increasing the revs? Might work out cheaper then replacing worn disk pads :rolleyes:?
Dont kill me i know feck all about cars

You are wrong. As long as you don't rev using your gas pedal fuel consumption is close to 0 when you are breaking with gears.

opinion guy

nightster1 wrote: »

I'm no expert, but my mechanic is. I run a common rail 3.0 6 cyl diesel, before using dipethane, I replaced a number of injectors due to dodgy diesel. The injectors were replaced under warranty (€2K cost). The diesel fuel was analysed and found to contain some detergents and water. The garage refunded the dealer with the cost of the repair. Apparently, impure diesel is quite common around the country. That was 70,000 miles ago. I was advised to use dipethane. It lubricates and cleans the fuel system. Since then I have had no issues, I have better fuel consumption, little or no black exhaust smoke and passed 2 NCT's without any emission issues.


http://www.dipetane.com/

I'm sure that there are other equally as good fuel treatments but this stuff works for me.

Interesting. I shall have to do further research.

Another question - occasionally I've seen it recommended on here to add small amounts of petrol to the diesel tank to improve efficiency. Does this actually improve efficiency or a urban legend ?

limklad

Jagle wrote: »

round limerick none of them are level, forever going up and down hills

There are no hills in which the Motorway around Limerick is on.Patrickwell to before the Bog of Doom & mire is flatter than the Tipperary stretches of the Motorway to Dublin which is full of Hills from Limerick Border to Nenagh.

by the way I would not call the stretch around the Ballysimon Junction a Hill, It is just a bump and a dip in comparison to other stretches of Motorways in the country.