Fuel saving tips thread

meester

Please post your ideas.

Here are some:

• Make sure your tyres are properly inflated. Proper inflation reduces rolling resistance and improves fuel consumption.
• Remove excess weight. Unnecessary junk in the car will use up more fuel.
• Avoid air conditioning. The alternative is to open the window(s). Below 50mph, opening the window will be a cheaper option. Above 50mph, the increased drag caused by open windows, means turning on the air con is better.
• Drive slower on motorways. The classic speed is 56mph, obviously in top gear, but even sticking to the legal speed limit of 70mph rather than 80mph will make a huge difference.
• Don't accelerate unnecessarily. If you see a red light ahead, take your foot off the accelerator, and coast. Likewise, for a 1 mile stretch of dual carriageway between roundabouts, accelerating to 70mph is wasteful. Braking is NOT the problem, there's no need to brake very slowly, but the unnecessary acceleration is the problem.
• Accelerate gently. Keep the revs low. The higher the rpm the more petrol used, much better to keep things gentle.
• Switch off the engine. If you will be waiting for more than 20 seconds, turn the car off: it's cheaper.
• Get low-rolling resistance tyres. These can improve mpg by 6% (proven). See http://greenseal.org/resources/reports/CGR_tire_rollingresistance.pdf http://en.wikipedia.org/wiki/Low-rolling_resistance_tires etc. The rolling resistance coefficient doesn't seem to be generally published, but Michelin market their Energy Saver tyre. At about £55 a corner, on 12,000 miles a year at 40mpg before, 43mpg afterwards, and £5.25/gallon, you'd save 20 gallons, or £100/year. If your tyres are getting on a bit, it would likely to pay to get these fitted.

Pew_Pew_Pew_Lasers!

meester wrote: »

tyres are properly inflated. Proper inflation reduces rolling resistance and improves fuel consumption.

Correct tyre pressures are a point of safety - not saving money.

meester wrote: »

Avoid air conditioning. The alternative is to open the window(s). Below 50mph, opening the window will be a cheaper option. Above 50mph, the increased drag caused by open windows, means turning on the air con is better.

Some vehicles use no more fuel with AC running than without AC running. And not running an AC system regularly will lead to leaks and the eventual failure of the system.

meester wrote: »

Drive slower on motorways. The classic speed is 56mph, obviously in top gear, but even sticking to the legal speed limit of 70mph rather than 80mph will make a huge difference.

People who drive slowly on motorways and who don't drive according to the conditions, shouldn't drive on motorways at all.

meester wrote: »

Don't accelerate unnecessarily. If you see a red light ahead, take your foot off the accelerator, and coast. Likewise, for a 1 mile stretch of dual carriageway between roundabouts, accelerating to 70mph is wasteful. Braking is NOT the problem, there's no need to brake very slowly, but the unnecessary acceleration is the problem.

Most engines use more fuel when coasting than they do when engine braking.

meester wrote: »

Accelerate gently. Keep the revs low. The higher the rpm the more petrol used, much better to keep things gentle.

Keeping revs low might actually force gearchanges too early, with the result being that the engine is below the most efficient rpm for the vehicle, increasing fuel consumption. Best to change gear keeping the engine in the power band.

meester wrote: »

Switch off the engine. If you will be waiting for more than 20 seconds, turn the car off: it's cheaper.

No it isn't, a lot of electricity is used when starting an engine, also wear and tear increases on the starter motor and battery, not to mention wasted unburnt fuel in the engine.

mark55man

just to support this thread, but doing many of things OP mentioned, I am getting 50 miles a tank more - that's about £40 a month. In terms of jounrey time added by doing 56 rather than 65 (usually by not overtaking a slower moving truck) its about 5 minutes each way a day.

200 minutes a month, £40 a month = £12 an hour !!.

tomstickland

Don't accelerate unnecessarily. If you see a red light ahead, take your foot off the accelerator, and coast. Likewise, for a 1 mile stretch of dual carriageway between roundabouts, accelerating to 70mph is wasteful. Braking is NOT the problem, there's no need to brake very slowly, but the unnecessary acceleration is the problem.

I agree with the answer, but the reasoning can be considered in another way. I consider the unecessary braking to the be problem.
Braking involves throwing away energy that the vehicle has.
It's better to cut the power earlier and allow the vehicle to dissipate that energy overcoming air and rolling resistance and slow naturally.

The most efficient way to drive would be to remove the power far enough away from a stopping point that the car could roll all of the way there, thereby being in a situation where no energy is thrown away over and above that needed to overcome the various resistances.
Now, in practice, it is better to use engine braking (zero throttle) because that way no fuel is used at all by the engine.

For the example of two roundabouts the same answer is arrived at. ie: no point in accelerating hard to 75mph and then standing on the brakes at the last moment because the fuel expended in getting the car up to speed is then thrown away as heat.

It is an interesting point though, because I believe that coming off the power earlier for known slowing points is the key to reducing fuel consumption.

The amount of work done needed to accelerate a car up to a speed is pretty much independant of the rate of acceleration. So if you wish to travel at 60mph there's not much difference in brisk acceleration versus taking 5 minutes to reach that speed.
However, when slowing down the amount of energy wasted can be significant.

Accelerate gently. Keep the revs low. The higher the rpm the more petrol used, much better to keep things gentle.

There is a school of thought that says a short burst of moderate acceleration is more efficient than a longer time spent gradually accelerating.
Regarding rpm, this rule does not apply right down to very low rpm. The most efficient operating rpm of a petrol engine is in the 1.5-2K area and at middling loads.

Switch off the engine. If you will be waiting for more than 20 seconds, turn the car off: it's cheaper.

There's another thread where we discussed the rate of fuel consumption whilst idling. The actual rate is very low.
http://forums.moneysavingexpert.com/showthread.html?t=911337&page=3&highlight=fuel+idling
About 1 litre per hour, which is 6.6 miles covered in a 30mpg car.
So each minute is worth about 0.1 of a mile. Say you drive 30 miles per day and spend 2 minutes sat in a queue. You're losing 0.2 miles in 30 which is 0.6%. On a 35mpg target that's a 0.2mpg difference.


Accelerate gently. Keep the revs low. The higher the rpm the more petrol used, much better to keep things gentle.
Switch off the engine. If you will be waiting for more than 20 seconds, turn the car off: it's cheaper.

Without a doubt, savings can be made by anticipating so as to avoid unecessary increases and decreases in speed. I drove along the motorway at 70 dead for half an hour yesterday and in that time leapfrogged one car twice because they were driving in bungee fashion.
Fuel consumption also rises with speed squared when above about 50mph, so 60 is about 25% more fuel efficient than 70. Consideration has to be give to other traffic though, so I travel at 70 on motorways.

One thing I quite enjoy is that driving efficiently does not mean just driving slowly. If you anticipate properly and maintain momentum you actually still cover ground at a decent rate. I've actually had to chuck away some of my gains overtaking those who insist on jerking along at 45mph down smooth A roads.

You can safely inflate tyres by a few psi over the book figures. Some driving manuals tell you to do so to improve handling.

meester

A few other things:

roof boxes are very bad for aerodynamics. Particularly at high speeds they should be removed.

also, on motorways, slipstreaming lorries (hopefully at a safe distance) gives a substantial fuel saving http://www.autobloggreen.com/2007/10/28/mythbusters-drafting-10-feet-behind-a-big-rig-will-improve-mile/

you can also time traffic lights by coming off the throttle when they are red

Sunroofs are not a good idea at high speed either.

100 tips here:

http://ecomodder.com/forum/EM-hypermiling-driving-tips-ecodriving.php

meester

Pew_Pew_Pew_Lasers! wrote: »

Correct tyre pressures are a point of safety - not saving money.

There are many reasons to maintain correct tyre pressure. Saving money is just one of them.

People who drive slowly on motorways and who don't drive according to the conditions, shouldn't drive on motorways at all.

Motorways have two or more lanes, to permit multiple speeds. To suggest that you shouldn't be on the motorway if you are planning to maintain a speed of around 56mph is stupid, given that a substantial proportion of motorway traffic is limited to this figure anywhere. Also, it's not an absolute. You can often find a caravan or HGV, and sit behind it, to avoid impeding traffic flow unnecessarily.

Most engines use more fuel when coasting than they do when engine braking.

If the throttle is not open, then the engine still uses a minimal amount of fuel, this shouldn't change if you are braking or coasting, because you have not requested any acceleration. I guess ultimately not using the brakes is better because it implies less throttle used beforehand.

Keeping revs low might actually force gearchanges too early, with the result being that the engine is below the most efficient rpm for the vehicle, increasing fuel consumption. Best to change gear keeping the engine in the power band.

This is generally not true. Being in a higher gear means the car goes faster for the same amount of work. But in top gear at maximum torque your car will be generating a substantial amount of air resistance due to the high speed. This is part of the reason for the 56mph speed limit, even if it is not maximum torque.

No it isn't, a lot of electricity is used when starting an engine, also wear and tear increases on the starter motor and battery, not to mention wasted unburnt fuel in the engine.

Electricity? Do you plug your car in? It is true that the amount of fuel used starting a warm car is minimal, and thus 20 seconds is accurate.

tomstickland

Many people drive that close to lorries anyway, if you look at the 100ft image:

tomstickland

Pretty good list this one

http://ecomodder.com/forum/EM-hypermiling-driving-tips-ecodriving.php

When you're going for a good mpg you really notice how jerky and unalert a lot of drivers are. The worse one for me is timing a set of lights that go green, but the car in front takes 3seconds to move off, ruining the plan.

vikingaero

tomstickland wrote: »

Many people drive that close to lorries anyway, if you look at the 100ft image:

If you're going to practice drafting for a meaningful effect two things will probably happen:

(1) You'll get pulled by Plod
(2) Your body will be cut from the mangled wreckage of your vehicle when the HGV performs an emergency stop.

:rolleyes::D

scbk

101) Minimize accessory loads

Minimize use of electrical and mechanical accessory loads when safe and/or practical (lights, defrost, blower, electric heated seats, dvd players/screens, heated mirrors, etc).

Good point, I see so many people driving round with lights on when visibility is fine. Must use a fair amount of extra fuel over the lifetime of a car

tomstickland

vikingaero wrote: »

If you're going to practice drafting for a meaningful effect two things will probably happen:

(1) You'll get pulled by Plod
(2) Your body will be cut from the mangled wreckage of your vehicle when the HGV performs an emergency stop.

:rolleyes::D

But look at the top image - people already drive that close to lorries.