Fuel saving tips thread

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The real way to save fuel is to not make journies that are unnessesary in the first place, plan your journies wherever possible to avoid duplication.

AdrianHi

meester wrote: »

Are there any properly controlled studies documenting an improvement using these fuels?

For BP Ultimate Diesel there is.
http://www.bp.com/sectiongenericarticle.do?categoryId=4005641&contentId=7009028
I cannot find it now, in the past I have a read a report on a test on an Audi A6 2.7 TDI, brand new never been driven. They rigged the car up to run 3 cylinders on standard BP and 3 cylinders on BP UD drove 6000 miles and then opened up the engine block to look inside. The BP UD cylinders were virtually as new, the standard fuel cylinders were already showing soot and carbon deposits. This particular test was to investigate the cleaning properties.

Myself, I've switched to and from BP UD or standard Diesel with and without Millers enough times to be sure enough in my own mind that the claimed benefits are true to make the decision to buy and use BP UD (at the right price) or the Millers additive. There are many diesel car owners who report the same results, but a few who don't seem to notice any benefit at all.

tomstickland

thescouselander wrote: »

When driving on the motorway I usually find that using cruise control produces better MPG as it does a better job of maintaining a constant speed.

It depends on whether you enjoy the challenge. I like seeing if I can hold an absolutely steady speed, though I will sometimes adjust it up a bit if I'm using the outside lane and faster traffic is coming up behind.

thescouselander

meester wrote: »

True, but you can technically get better fuel consumption without it, by keeping constant throttle. Cruise control works against gravity, which is bad on hills.

Yes, I have heared that said but I'm not sure it stands up to scrutany.

If you are going up hill the cruise control will open the throttle to maintain the same speed - the engine will use more energy but the car has gained potential energy as it gains hight - essentially the extra energy has been stored as potential energy.

When the car goes down the hill that potential energy is recovered as gravity helps the car down the hill and the cruise control will close the throttle.

The extra energy used going up hill should be cancelled out on the down hill leg.


I think the reason why less fuel is used keeping a constant throttle is because the car will slow down going up hill causing less drag.

Pew_Pew_Pew_Lasers!

meester wrote: »

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

No, there is only one reason to maintain correct tyre pressure, and that is safety.

meester wrote: »

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.

If you maintain a speed of 56mph while overtaking other traffic you will help create a bottleneck and reduce overall speeds. Or does elephant racing not happen?

meester wrote: »

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.

When coasting an engine is using a small amount of fuel to run. When engine braking, on many cars it is using none. Engine braking is also safer than coasting as the vehicle's speed is more easily controllable.

meester wrote: »

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.

Keeping rpm low while changing gear means that the engine will be labouring on the upchange. Try cycling up a hill in top gear on a bike at 5mph and see how well your theory holds up.

The 56mph speed limit for HGVs is a useless piece of EU legislation.

meester wrote: »

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.

Oh sorry, perhaps the starter motor has a fuel feed I didn't know about. Perhaps you could show it to me.

tomstickland

thescouselander wrote: »

Yes, I have heared that said but I'm not sure it stands up to scrutany.

If you are going up hill the cruise control will open the throttle to maintain the same speed - the engine will use more energy but the car has gained potential energy as it gains hight - essentially the extra energy has been stored as potential energy.

When the car goes down the hill that potential energy is recovered as gravity helps the car down the hill and the cruise control will close the throttle.

The extra energy used going up hill should be cancelled out on the down hill leg.


I think the reason why less fuel is used keeping a constant throttle is because the car will slow down going up hill causing less drag.

Such is the nature of the system that I expect that you find the downhill part doesn't fully compensate for the extra work needed on the uphill part.
I believe that you will get slightly better mpg by allowing the car to slow on the uphill part and then picking up speed on the downhill.

meester

Pew_Pew_Pew_Lasers! wrote: »

No, there is only one reason to maintain correct tyre pressure, and that is safety.

That is reason enough, certainly, but to suggest there are no other reasons is stupid.

If you maintain a speed of 56mph while overtaking other traffic you will help create a bottleneck and reduce overall speeds. Or does elephant racing not happen?

Who said you had to maintain 56mph while overtaking? You are not limited, you have to use common sense. But if there is a dual carriageway with a lorry at 56mph in the left lane, you don't need to overtake it, you will save money by being in the left lane.

Keeping rpm low while changing gear means that the engine will be labouring on the upchange. Try cycling up a hill in top gear on a bike at 5mph and see how well your theory holds up.

Nonetheless, real-world studies show that you will do better at 1800rpm in top gear than 2600rpm in the lower one.

The 56mph speed limit for HGVs is a useless piece of EU legislation.

Your opinion is irrelevant though, given that it exists, and many vehicles will be sticking to it.

Oh sorry, perhaps the starter motor has a fuel feed I didn't know about. Perhaps you could show it to me.

Not sure what your point is. You are not paying for the electricity in a car, it is stored for free as a result of previous motion.

AdrianHi

meester wrote: »

That is reason enough, certainly, but to suggest there are no other reasons is stupid.
[snip]
Not sure what your point is. You are not paying for the electricity in a car, it is stored for free as a result of previous motion.

I've seen the results of studies done on various fuel saving measures and moderately low tyre pressures don't make much difference to fuel consumption, but the life of the tyre is reduced considerably and then there is the safety implications already mentioned.

You are paying for the electricity in the car, it comes from the fuel, no where else for it to come from. It is the fuel that gets the car moving in the first place. Stopping the engine when not in motion in traffic is worth while and I've heard 30 seconds as a minimum worthwhile stop before.
I cannot find the magazine article now to confirm the saving, but stopping and starting the engine in urban traffic improves MPG by around 8%-10% in the urban cycle on the EU tests. BMW have measured this with the automatic Start Stop feature on their latest 4 cylinder manual transmission cars.

ABN

meester wrote: »

Quote:
Oh sorry, perhaps the starter motor has a fuel feed I didn't know about. Perhaps you could show it to me.
Not sure what your point is. You are not paying for the electricity in a car, it is stored for free as a result of previous motion.

There are soooo many errors and misconceptions in this thread it's incredible.

But the one that stands out the most is the above.

Any item that uses electricity also uses fuel. The charge taken out of the battery has to be replaced. This places an increased load on the alternator which in turn places an extra load on the engine and hence lowers the fuel economy.

Mobeer

ABN wrote: »

There are soooo many errors and misconceptions in this thread it's incredible.

But the one that stands out the most is the above.

Any item that uses electricity also uses fuel. The charge taken out of the battery has to be replaced. This places an increased load on the alternator which in turn places an extra load on the engine and hence lowers the fuel economy.

When you coast to a stop the battery is charged from the rotation of the wheels. Then when the engine is restarted energy is taken from the battery. This makes more sense that braking harder when slowing down, then running the engine whilst stationary, then using power from the battery when restarting the car.