Fuel Consumption

Biro

Anan1 wrote: »

If the aim is to stop the car then using engine braking makes sense (although starting to coast earlier wiould use less fuel). If the aim is to conserve momentum down a hill, though, you'd be far better off coasting in neutral. As far as I can see, though, the bottom line is that car in gear + no throttle = lots & lots of frictional losses with nothing much useful to show for it.

No, in practice it's better to leave the car in gear rather than coast. In a car that reads litres used per 100km's with live updated information you'll see that clearly. Going down a hill in gear does cause more momentum lost than in neutral, but very little. All you need do is lightly use the accelerator to keep the same momentum. As the hill will be helping the car it'll be using something like 2.5l/100km. If you clutch in it'll go up to around 5.6l/100km.
Same story stopping, coming to almost a stop, going down steep or slight hills, I've tried them all.

Biro

kluivert wrote: »

I was watching the TG espiode where Gerry takes an Audi A6 4l TDI from London to Glasgow and back on one tank of fuel.

Am near sure he said to push in the clutch, which closes the throttle which it turn stops fuel being pumped into the engine, maybe this is only for diesel engines I dont know. He also said you gradually slow down and means less breaking effort therefore less fuel consumption on the braking as well.

It was the A8 4 litre V8 TDi. And he said the exact opposite. He said DON'T clutch in when slowing down as when engine braking modern cars shut off the fuel to the cylinders.

Anan1

Biro wrote: »

No, in practice it's better to leave the car in gear rather than coast. In a car that reads litres used per 100km's with live updated information you'll see that clearly. Going down a hill in gear does cause more momentum lost than in neutral, but very little.

Surely this depends on your speed/the gearing of your car/the compression ratio of your engine etc. I regularly use engine braking when I want to lose momentum.

Biro wrote: »

All you need do is lightly use the accelerator to keep the same momentum.

But won't this negate the advantage of injector shutdown on a trailing throttle?

Biro wrote: »

As the hill will be helping the car it'll be using something like 2.5l/100km. If you clutch in it'll go up to around 5.6l/100km.
Same story stopping, coming to almost a stop, going down steep or slight hills, I've tried them all.

These figures are clearly specific to your car. Are you sure your trip computer works accurately when coasting?

Biro

Anan1 wrote: »

Surely this depends on your speed/the gearing of your car/the compression ratio of your engine etc. I regularly use engine braking when I want to lose momentum.

But won't this negate the advantage of injector shutdown on a trailing throttle?

These figures are clearly specific to your car. Are you sure your trip computer works accurately when coasting?

I don't see why you're finding it so difficult to believe. I could answer your questions but I'm beginning to think it won't matter.
Ring a manufacturer and ask, they'll tell you. I'm serious though, not trying to be smart. They'll oblige with an answer. Ring someone like VW UK, or VW Ireland (be sure it's HQ, not just the dealer down the road) and I'm sure they'll confirm.

theitking

DONT RUN TOO LOW

Two things that made me think twice!

Firstly,
I had to get the fuel filter changed twice within 8 months! :O It was FILTHY! Ya'd be a fool to think that every drop that pours from the pumps is free of dust, grime and impurities. It all settles at the bottom of your tank, anyone who thinks differently, drink a cuppa using the last drop in the kettle and come back to me lol

Secondly,
Most modern delivery pumps (the one in the tank) run completely submerged in the fuel - nicely cooled and making light work of things.
When you run low it runs at a higher temperature with no fluid keeping it cool and lubricated.

Mine went less than two weeks ago because of this - Check my history for proof lol :cool:

Anan1

Biro wrote: »

I don't see why you're finding it so difficult to believe. I could answer your questions but I'm beginning to think it won't matter.

If you don't want to answer,that's ok.

Biro wrote: »

Ring a manufacturer and ask, they'll tell you. I'm serious though, not trying to be smart. They'll oblige with an answer. Ring someone like VW UK, or VW Ireland (be sure it's HQ, not just the dealer down the road) and I'm sure they'll confirm.

I know you're being serious, but have you ever tried calling VW Ireland to find out about anything?

Biro

Anan1 wrote: »

If you don't want to answer,that's ok.I know you're being serious, but have you ever tried calling VW Ireland to find out about anything?

Point taken!
Try Toyota UK or someone! But I'm convinced that it's worse for economy to freewheel.

tontooreilly

1. Keeping your car well maintained –Make sure your car is serviced
according to the manufacturer’s recommendations. Under-serviced
engines can reduce fuel economy by ten percent or more. Catalytic
converters are environmentally friendly – but they need to be at the
correct temperature which takes around 6-10 mins.
2. Turning your engine off - Avoid excessive idling if you’re stopped for a
long time.
3. Turning off air conditioning - Air conditioning uses engine power to
operate.
4. Only half fill your fuel tank- Why fill the tank up to the very brim? Be a
tank miser. If you do so, you may be carrying around additional
fuel, which in turn means that you have more weight on board than
is necessary. That extra weight will itself reduce fuel efficiency.
5. Checking your tyre pressures – Correctly inflated tyres reduce
rolling resistance.
6. Sticking to the speed limit – Drive faster and you’ll use more fuel. Doing
90Kmh uses 25 per cent less fuel than 120Kmh.
7. Park in the shade – Parking in a cooler spot will minimise fuel evaporation
and make you less reliant on air conditioning.
8. Use cruise control where fitted – This will helps you avoid
unnecessary ‘surging’ on the motorway.
9. Reversing into parking spaces. When you start off again, the
engine will be cold and at its most fuel inefficient. This will enable
the vehicle to drive smoothly away without having to reverse
(reversing is generally a high revving manoeuvre) when the engine
is cold.
10. Remove unnecessary clutter from your car-More weight means
more fuel consumption. Remove unnecessary boot luggage
and avoid heavy accessories and wide tyres that add rolling
resistance

Anan1

Biro wrote: »

Point taken!
Try Toyota UK or someone! But I'm convinced that it's worse for economy to freewheel.

I know you are. But understand that i'm not being gratuitously difficult when say that I can't see how introducing extra drag into the equation can improve fuel economy.:)

Quazzie

Driving around with under half a tank is a bad idea. Assuming your car has a standard 70L tank when full it weights 70kg, half full 35 kg. When you drive around with less petrol in your car you increase the chances of taking foreign contaminants into your fuel filter and eventually into your engine, thus being detrimental over a span of time. The 35kg you are saving equates to half the average person, or a third if new obesity findings are to be believed.

Unless you are looking for hardcore fuel economy savings i.e <.5mpg then I wouldn't worry about my full tank.