The Economical Driving Discussion Thread

[djefk]

Go that's a boring title... But with petrol rapidly approaching £1.50 a litre (and diesel even closer), could we discuss a few tips that people have found to increase their fuel mileage? I like to think I'm a fairly economical driver without being downright slow myself and wondered if this is of interest to others.

I'm not talking about discussing things like check your tyre pressures / maintain your car / give it a clear out or other things we've all heard before that are unaffected by how the car is driven, I mean actual driving style habits that you have actually noticed make a difference to the MPG figures you're getting once implemented.

For example, I read that when BMW researched into it they found that best practise for fuel economy is to accelerate fairly quickly to your target cruising speed before backing off the throttle just enough to hold your speed steady - This makes sense when you think about it in my opinion, what about yours?

What other pearls of wisdom can people give that could save us all a few quid? I for one would be interested to hear!

[speedy88]

I don't do it often, I seem to get high 20s no matter how I drive. But when I do - I tickle the throttle and use the engine torque to get the car up to speed keeping it under 2000k and changing gear as soon as I can. Plus I knock it out of gear on hills and sit on the brake.

[MK2VR6]

Walk, car share, take the bike, lose weight, tidy out the boot and glovebox. Then stick your foot down and have fun the rest of the time

[Ryannn]

I've just downsized my engine, doubled my mpg! No help I'm afraid

I have recently started using vPower fuel. I get more mpg which outweighs the slight extra cost!

[scruff]

Stay off boost...

[VIP]

Apr 20, 2012 22:13:14 GMT speedy88 said:

Plus I knock it out of gear on hills and sit on the brake.

If your car is injection, this is false economy, you're better off leaving it in gear as it will use no fuel at all in overrun providing engine speed is higher than the idle circuit (usually <1200 rpm).

[djefk]

Apr 20, 2012 22:30:09 GMT Ryannn said:

I've just downsized my engine, doubled my mpg! No help I'm afraid

I have recently started using vPower fuel. I get more mpg which outweighs the slight extra cost!

Unless it's modern that has an ECU sophisticated enough to constantly adjust the timing, any ideas on why this makes a difference? I've heard this before myself.

[djefk]

Apr 20, 2012 22:18:52 GMT MK2VR6 said:

Walk, car share, take the bike, lose weight, tidy out the boot and glovebox. Then stick your foot down and have fun the rest of the time

Thanks ;D

I was actually hoping to actually get some real input to this however...

[RobinJI]

With regards to the coasting down hills thing, I've been wondering recently what the deal is with it when it comes to mechanical pump diesels? Do they have any sort of over-run cut off? I don't really know anything about the workings of diesel pumps, so I've been kind of assuming that my Passat wouldn't, so I've been coasting down the odd hill.

In some situations coasting can be better even if there is a full cut off, because you manage to go further off the throttle than if you stay on it. For instance there's a fair few down hill bits of the A303 where I find my Passat will stay at 70 if out of gear, but if I leave it in 5th then I have to tickle the throttle to keep it at 70, so I'm putting in more fuel than it would be putting in at idle, because it's overcoming the friction of the drivetrain, and the engine at a higher speed than idle.

Just driving normally, I tend to sit at 80/85 on the motorway, 65 on A-roads and just keep up with traffic as smoothly as possible, and my 1.6td Passat estate returns a consistent 47mpg. Over Easter I did a tank driving normally, but not budging over 75 on the motorway, which got me up to 52mpg. Then on the next tank I started coasting occasionally, sitting at 65 on the motorway, and avoiding the brakes at all costs by letting off long before junctions so I'd coast up to them at a safe speed, which got me up to 56mpg, despite a lot of driving around hilly, twisty Somerset back roads.


One thing that I often think about, is that driving slower on the motorway can sometimes be a false economy. If times not worth anything to you, (as it is for me as an unemployed student), then pretty universally more mpg = good. But when I had a part time job, and was always turning down hours because I didn't have time for it, I was always thinking about it.

For instance my drive home from uni is ~150 miles, and mostly motorway or dual carriageway. At 60mph, that would take 2.5 hours, and I should get ~60mpg, making it cost me £16.80 if I pay £1.48 for diesel. Now if I do it at 85mph, it'll take ~1:45, and I'd probably get ~50mpg, costing me £20.16. So I've essentially just spent 45 minutes saving my self £3.36, that's £4.48 per hour, I'd hope most people on here earn more than that!

(I'd tended to find a half way house and just sit at ~70, because I enjoyed driving and listening to music more than selling cheep bikes at Halfords!)

[Ryannn]

Apr 20, 2012 22:46:14 GMT djefk said:

Apr 20, 2012 22:30:09 GMT Ryannn said:

I've just downsized my engine, doubled my mpg! No help I'm afraid

I have recently started using vPower fuel. I get more mpg which outweighs the slight extra cost!

Unless it's modern that has an ECU sophisticated enough to constantly adjust the timing, any ideas on why this makes a difference? I've heard this before myself.

My Saab did it, but that was ecu driven. I've had the timing and mixture set up on my mini with vPower and it runs better, don't know why though :/

[Dorset_Clive]

One of the biggest things is to read the road - the least changing of speed you can do, the better the economy.

Traffic ahead? Get off the throttle early and let the speed naturally scrub off. Hopefully by the time you reach the 'blockage' it will have cleared. It helps to leave a bigger than normal gap between you and the car in front.

I have no idea if it is true, but there's an internet rumor that manufacturers tune their ECUs to give max economy at 56mph in line with the statutory performance figures. True or not, around that speed seems to be a sweet spot between making progress and burning too much fuel.

[speedy88]

Apr 20, 2012 22:36:56 GMT VIP said:

Apr 20, 2012 22:13:14 GMT speedy88 said:

Plus I knock it out of gear on hills and sit on the brake.

If your car is injection, this is false economy, you're better off leaving it in gear as it will use no fuel at all in overrun providing engine speed is higher than the idle circuit (usually <1200 rpm).

I agree, should have mentioned I have a dirty dirty carb

Robin - I had a rotational diesel pump on the peugeot and I'd see 5mpg more coasting down hills. This was commuting around Bristol too. I came to the theory that it was injecting more as the car during engine braking is rotating the engine more times - therefore still inputting the "idle" (or throttle off) amount of fuel. Can't think what else it would have been.

Wish I'd had the balls to try engine off down hills, there's some long roads round here you can coast for miles down. You can forget about brakes though!

[RobinJI]

Apr 21, 2012 0:09:57 GMT speedy88 said:

Wish I'd had the balls to try engine off down hills, there's some long roads round here you can coast for miles down. You can forget about brakes though!

I've been wondering about wiring up an over-ride switch to the fuel cut-off solenoid so I can kill the fuel as a when I want without loosing all the lights and other ignition switched goodies. This'd be even better if combined with an electric vacuum pump to keep the brakes working. Any common donor cars for electric vacuum pumps?

If you were really worried about the brakes then as long as it's in gear you'll still get a vacuum from the pump, but I'm not sure I'd like the idea of the diesel pump spinning away without any fuel lubricating it.

I thought that would be the case with the diesel pumps, they'd have no way of knowing to cut fuel completely, so your theory makes sense, they probably do just chuck in an idle amount per revolution, but more often because of the higher speed.

[Foxy]

don't buy a 4.2 Jag with fuelling gremlins!

[speedy88]

Apr 21, 2012 0:21:03 GMT RobinJI said:

Apr 21, 2012 0:09:57 GMT speedy88 said:

Wish I'd had the balls to try engine off down hills, there's some long roads round here you can coast for miles down. You can forget about brakes though!

Lots of stuff....

Yeah interesting but agreed, especially with the feeble Lucas pump on the pug I wouldn't want to un-lubricate it.

[RobinJI]

Yeah, I think you're right there, I wouldn't want to risk cutting it with the engine still spinning away for any real time, the idea would be to cut the fuel out of gear, just so it's not idling away, but then you'd loose the vacuum, hence the idea of an electric pump.

[speedy88]

Ahh, got it. Alternatively you'd hope that if your vacuum system was good enough that there's be enough in there for at least 3 pumps of the brakes. I mean, it's asking a lot of peugeot but...

[stealthstylz]

If I can be bothered to drive nicely I just go gently on the throttle and change gear early, then coast to a stop at junctions (left foot resting on the brake so its just enough to put the lights on)

[SamR380]

I got 32mpg on my last tank in the mx5, mostly by driving at 65 on the motorway. Can't hear the radio if I go any faster anyway.

The rest of the time I nail it though. Heel and toe into corners and roundabouts, rather than coasting in gear

I use tesco 99, but I don't think it makes much difference to the economy.

[trevorbrady]

I know it's not a "driving style" tip and it takes some dedication but keeping a "fuelly.com" account helps me keep an eye on fuel economy with my 95 Passat daily driver (is it retro yet? ). www.fuelly.com/driver/trevorbrady/passat

After you fill up (and I mean fill up, not just throw in 20 quid's worth) you log the price per litre, the amount filled and the odometer reading (not the trip meter) and it does the sums for you and provides you with a nice graph mapping the variation in MPG.

I experimented with putting in a mega high final drive gearbox into the passat to see if I would get intergalactic fuel economy but if anything it hurt fuel economy. The gears were too long for the pretty low power band of the engine so I was having to rev it out further before changing up and it really felt like I was labouring the engine trying to cruise at 60 in 5th. It was revving too low for the road speed. I ended up putting the original gearbox back in as I wanted to tow a car on a trailer and the high final drive gearbox would have been hell with it.

One other thing that fuelly has taught me: my car costs me 15c (euro cents BTW) per mile to run in fuel costs. It makes NO sense to drive out of your way for cheap fuel in the next town/village. If the town is 5 miles away, it costs 10x15c there and back so unless you save more than €1.50 on the total fillup you're wasting money, not to mention time. This has taught me that the best time to buy cheap fuel is when you see it. Even if you're only half empty, fill up for cheap instead of draining the tank and driving further for cheap fuel. The other thing, filling up before you need to means you're not always forced to spend more than you need to on expensive fuel because the red light is on and it's the next available station.

Reducing drag is a big one too. I find MPG suffers if I forget to remove the roof bars from the car.