Fuel cost: How to save petrol and diesel

The article says there are three tests, ie city, 56MPH, and 75MPH.

It must have a thermostat in?

My car has two tyre pressures shown on the door pillar. Normal, and eco. Eco is a tad higher.

It is still not that far from the truth. The exact speed for optimum fuel consumption for maximum range varies with the vehicle aerodynamics but the losses due to drag go up as the cube of the speed AOTBE.

Somewhere between 50 and 60 mph airspeed is about where the aerodynamic drag begins to dominate the forces acting on the vehicle. I'd hazard a guess that for a big white van the optimum speed for best mpg is even slower since they have all the aerodynamic styling of a brick.

It depends how aggressive you have it set. I don't see any noticeable change with or without aircon. I do see a big difference when my wife drives. She gets ~840 miles out of a tank where I only get ~750 miles. (entirely down to average driving speed)

Car does a lot of long distance journeys at motorway cruise speed. It's lifetime average speed is 40mph and it does an average 64mpg.

A pedal to the metal guy who is either hard on the accelerator or the brake which is just about the worst possible case for fuel consumption.

Higher speeds, acceleration and braking all uses more fuel.

My car is 'aware' of upcoming downhill sections and junctions, it lights up a green "foot off the accelerator" light, but when it's on cruise control it doesn't always take its own advice, I can drive more economically than it on the same journey.

On a straight and level section, with sufficiently light traffic that my speed doesn't have to vary depending on other drivers, at low 50s mph I get high 50s mpg, and vice-versa.

The other day I managed 42mpg on a main road. As soon as I spent the next 40 minutes looking for a place to park that ruined it to 38mpg...

I've been running on tesco 'E0' fuel lately, which makes a big difference economy-wise, compared to E10, including the non dual-carriageway start and end of the journey, mid 40s is about what it ends up as. If it's town driving, forget it ...

The air-con itself doesn't "know" anything it is just the system as a whole requires more energy this ultimately comes from the engine . Which requires more fuel to provide enough energy for the road wheels and the air-con. Similarly driving without the radio on and the lights off also save fuel, OK not a lot but every little helps.

In April.riving down theM6 past the Lake District in pouring rain, I noted that my fuel consumption was noticably affected

Not sure if you’re referring to the air con and running it for dehumidification but the drag caused by wet roads is significant. The more water your tyres have to shift, the more power required to overcome the drag. Much more noticeable in an EV.

Tim

My 1.6 HDi diesel averages about 55 mpg for a mixture of 40-50 country lanes and 60 main roads, with relatively little in-town 20-30 driving. And that has been fairly constant throughout the car's life - it's now 14 years old and has done nearly 190,000 miles.

The best basic advice is go easy on acceleration, keep engine revs low & where safe & not inconvenient coast to junctions.

The idea that one cannot accelerate from a coast is silly, this is not the 1930s when getting a car in gear can be difficult & slow. And the idea that one would need to floor it in an instant when approaching a stop in town is also very unrealistic.

Is this 97 octane that Esso supply ?.

I made a trip to Wales and back recently. 380 miles round trip and about 2/3rds on the M4, the rest A roads.

The tank was 1/4 full when I left and I put in £60 of Esso synergy 97 octane (no ethanol) at 186.9p, which is 32.1 litres. The fuel gauge was only slightly below the 1/4 mark on my return so that is close to 50 mpg.

I do less than 3,000 miles a year so I prefer to pay a bit more for non-ethanol fuel since the car is mostly unused.

Probably more accurate to say esso distributed, but supplied by greenenrgy

It's one of those wanky websites where you can't see it all until you scroll down the page (back to 2005 in this case).

Taking a number of trips Canterbury <-> Lewes at the minute as FiL is in hospital. Typically getting 65 to 70 mpg for the 2-hour journey (cross country, no motorway).

While that is good, anyone should be able to figure that out for themselves. Although I have given up trying to train SWMBO in the matter.

Of course, and the green light is usually too late in coming on, if you only take your foot off when it says so, you'll arrive at the junction without having recuperated much energy (the feature is part of stop/start).

It tells you other obvious things like "don't have the aircon on while the windows are open"

Maybe not a universal option but I find staying at home saves me a fortune in petrol and diesel costs.😎

I'm surprised that coasting (either in neutral or in gear with the clutch down) is *still* being recommended. As I understand it, most cars with fuel injection and an engine management unit will use *more* fuel when the engine is disconnected from the wheels, because a small amount is needed to keep the engine idling, whereas if the car remains in gear and the driver lifts off the accelerator, the engine management will cut the fuel *completely* because the momentum of the car is sufficient to keep the engine turning.

So in a car with fuel injection, coasting is *counter-productive*.

I can certainly see it with the instantaneous fuel consumption reported by the display on my car. If I press the clutch and/or change into neutral and take my foot off the accelerator while travelling along, the fuel consumption changes from 50-odd mpg to about 200 mpg. If I remove my foot while the car is still in gear (eg 6th), the consumption instead changes to

OK, coasting imposes less retardation on the wheels than remaining in gear, but normally you coast as a precursor to braking to a halt, so it makes very little difference whether you brake entirely with the brakes (when in neutral) or brake with the assistance of a very small amount of engine braking (when in gear).

Coasting *was* beneficial with carburettor cars, because the higher engine speed when remaining in gear would tend to draw in more fuel-and-air mixture past the mostly-closed throttle, than if the car was in neutral and the engine was idling. I say "mostly closed" because the throttle flap has to remain slightly open so the engine will still idle with no accelerator input: it can never close and cut off the fuel (and air) entirely with a carburettor.

I tend to accelerate fairly gently, unless I'm pulling out of a side road into traffic where the gaps are small and I need to get up to the speed of the traffic I'm joining as fast as possible. I try to remain at a fairly constant speed, reading the road and lifting off the power if I anticipate I will need to lose speed, partly to save wear on the brakes and partly because it uses less fuel than remaining under power for longer and then having to brake harder when I'm closer to the hazard that I'm slowing for. It also makes for smoother driving that being constantly either powered or else braking with no intermediate no-throttle-but-still-in-gear. When I approach traffic lights, I *try* to keep rolling slowly: sometimes I'll still need to stop, but sometimes the lights will change just before I reach them and I can accelerate back up to normal speed from (maybe) 5-10 mph rather than from rest, and so using a little less fuel.