A way to use less petrol?

ReductionQueen wrote:

Having a spare tyre isn't a legal requirement, but if you have one it's the law for it to have a legal tread and no damage, i.e. if you fit it, it should be legal to drive on it.
However, empfun if you call the RAC with a puncture they will ask you if you have a servicable spare. As I always do, I don't know what they will say if you don't, or how the AA handles such sitiuations. They may either refuse you a patrolman until you have a spare wheel, or recommend you to a mobile tyre fitter, which will cost you.

My Fiat Punto was purchased new in March 2004. Instead of a spare tyre, it is provided with with a container that you put on the valve to pump up the tyre and seal any leak at the same time. Of course, it is not much good for any high speed blowout!

Fiat also provide three year AA cover on new car purchases, so it would be perverse if the AA refused to come out simply because you do not have a spare tyre!

To be boring and go back to the beginning for a moment - 40 litres of fuel weighs about 29 kg not 40 (less dense than water); also the tank will be average quarter full instead of half, so the weight saving effect will be less than fuzyfelt hopes, maybe 7 kg average.

Plenty of good advice above; I would add that under load eg going uphill or accelerating it is most efficient for the engine to be at the speed where the best torque occurs; this is another thing in favour of diesel (typically 2000 rpm - right in the middle of normal driving speeds).

On wheels/tyres, I think you can take it too far. A normal size (if you have the choice, sorry) will eventually be used, so I reckon this is cheaper overall than the redundant spacesaver. And in fact, on a long trip abroad with some nighttime driving I will take 2 spares (I once spent 3 hours in a German town finding the right size, and it cost £75 vs £45)

Become something of a forecourt price nerd; that will save more than the weight saving. Sometimes the supermarkets have vouchers for fuel if you get your groceries there; and reward/visa points. So effective fuel price varies about 76 to 88p.

Silent_Bob wrote:

Sorry to disagree but you're wrong. All fuels have to conform to a rigorous standard procedure. i.e. Sainsburys unleaded and super is the same as BP's.

They all have to meet a minimum spec, eg EN590 in the case of diesel, and they all do, but this doesn't mean manufacturers can't exceed it, for convenience or marketing advantage. Eg the earliest Super Unleaded sold in the UK in the late 80s was typically 100 to 101 octane because for the quantities involved it wasn't worth blending it down to the 98 required to make it equivalent to 4-star.

Further eg: sulphur in diesel was reduced to 500ppm from late 1996, but the majors all went to that spec a year early so they could brag about it in their ads. The stuff they sold to supermarkets throughout was the old, cheaper 2,000ppm spec, which is worse for engines because sulphur wears them out.

Additionally most of the time they fill up from the same fuel depots. There's one near me and I regularly see Esso, Shell, Texaco, Sainsburys tankers etc filling up there - and this is a BP depot.

And it contains a dozen or more tanks, filled with fuel of varying specs, supplied into it either via the UK oil pipeline or by direct pipe from a nearby refinery or oil seaport. Which tank is used to fill DTWs depends on who the fuel is going to. It is very easy for a terminal to segregate different qualities and supply accordingly.

As for the weight of fuel making a difference it does at 1kg a litre that extra half a tank makes a huge difference. On half a tank I get about 33-35 mpg, but this drops to 28-30 on a full tank when doing the same driving week in week out.

The reference density for gasoline is actually 0.755kg/litre, 0.845 for diesel, so a 40-litre tank weighs 30kg or about 66lbs when full.

If you fill up, then drive the car till the tank is almost empty, the average weight of fuel would be 15kg. If you half-fill it and then always half-refill it when almost empty, the average weight of fuel would be 7.5kg. I find it very unlikely that a weight reduction of 7.5kg, well under 1% of the vehicle's weight, can possibly improve your fuel economy by 10 to 25%. If it did, I think you would find the car manufacturers would reduce the size of the fuel tank in order to fiddle the mpg results they use in their ads. If you want to reduce the weight carried, lose weight and drive naked.

Driving a fuel hungry sports car that requires the highest RON rated fuel I can get (Optimax) which is overpriced requires use of the fuel saving measures outlined.

I drive a convertible and find that shaving and polishing my head (I recommend Halfords' own brand), and only wearing wraparound shades while driving with the roof down, adds a good 10% to fuel economy, owing to better airflow.

empfun wrote:

2) Let your engine warm up fully if you have time before you drive it.

Waste of fuel. The fastest way to warm an engine up is to drive away.

4) Change your engine and transmission oil regularly.

Or use a synthetic and change it every 2 years instead of twice a year. As well as saving on oil changes the thinner oil improves fuel economy.