Fuel Consumption

Boskowski

MYOB wrote: »

No.

I'm entirely serious. You, however, appear not to be, or at least your attempts to type like someone not old enough to drive suggest that.

Ok, serious now.

I do not claim to be 100% sure what's going on here. I do however know that the alternator is usually connected by a belt to the engine. The engine turns the alternator, the alternator produces electricity and pumps it into the electrical consumers and also into the battery.

If however I was not aware that if you happen to need more power in the electric circuit of your car that the alternator was able to produce more drag on the engine so that the engine had to work harder to produce more electrical power.

Is that what you're saying? Because I don't think that's the way it works.
Your alternator produces whatever it produces, depending on the RPMs I guess. If you need more it either has it or it doesn't. It's not going to put more strain on the engine.

Air Condition is different, works off it's own compressor I learned which is either on or off. So on means more work to do for the engine.

It's amazing with how much conviction people are telling me it's not making sense what I'm saying when so obviously it doesn't make sense what they're saying.

Boskowski

Dades wrote: »

It's true - I see it all the time! (And my lawnmower is a 4.5 litre one... )

I have to admit I've seen in one of my very first cars something that might be confused with what the OP is saying.

I had a beetle and when she idled she had hardly enough revs on the alternator to power full lights. So they were kind of dimmed down a bit - yellowish- when I put down my foot the lights then got brighter.

But it's a one way street, I cant make the engine go faster by switching more electrical consumers on.

L1011

No, the alternator produces whatever power is needed. Where did you think it 'sent' the excess in times of low demand - you can't just discharge 70 amperes. How did you think you could run your stereo with the full beams on? Most importantly, how can you run your beams, radio, etc when the car is idling if you're insisting its 'connected to the engine revs'? The engine revs up solely because the alternator is putting a higher load on it - what did you think was doing this?

We're saying this with this much conviction because these are the facts. In my first post I told you a very quick example to demonstrate this happening: go out to your car, start it. Turn on the full beams and listen to the engine tone change as the alternator loads up. Your attempt to explain this above makes no sense itself, by the way.

Modern aircon can run off your electrics also. Doesn't always, but just like power steering its not compulsory for it to have its own pump these days.

Boskowski

MYOB wrote: »

No, the alternator produces whatever power is needed. Where did you think it 'sent' the excess in times of low demand?

Erm, to the battery?

All power produced by the alternator goes into the battery. The battery feeds the electrical system. There is no way the electrical system and the battery can 'ask' the alternator for more power which in turn will make the alternator rev up the engine. This is becoming ridiculous.

L1011

realcam wrote: »

Erm, to the battery?

All power produced by the alternator goes into the battery. The battery feeds the electrical system. There is no way the electrical system and the battery can 'ask' the alternator for more power which in turn will make the alternator rev up the engine. This is becoming ridiculous.

Wrong again. Fatally wrong if you were designing a car.

Battery charge voltage is variable on all modern cars. Also, if you over-charge a lead acid battery, the explode. Car batteries are lead-acid.

Could you PLEASE go and read something on car electrics before replying to this?

Voodoomelon

I never fill up to the brim as it would make no sense. Assuming petrol is approx 750g a litre, i'd be carrying around 71.25kg with me, the same as carrying an 11 stone man.

I fill to half way and then refill when I have 50km left in the tank. I also never brake when I don't have to, but I keep a safe distance from the car infront. 95% of the time there is no need to brake, just hover your foot above the pedal and you'll see that most of the time there is no need to use it.

ytareh

Im surprised no ones mentioned yet that the 'traditional' reason that people didnt let their car fuel level drop very low was to avoid letting the gunk/muck/debris etc in the bottom of the tank get through to the engine .Also have heard mentioned that condensation in the near empty tank was an issue especially in Winter.Anyone got a more expert view on these?

Boskowski

MYOB wrote: »

Could you PLEASE go and read something on car electrics before replying to this?

Did that and I have to admit that I was wrong and you are right. Makes me look pretty stupid I guess.

L1011

realcam wrote: »

Did that and I have to admit that I was wrong and you are right. Makes me look pretty stupid I guess.

Gracious in defeat, the easy option was never to reply.

stek

when parking, reverse into a spot rather than having to reverse out when the engine is cold. Im told this can save up to €100 a year in fuel.

After starting the engine, drive off straight away. Dont wait for the engine to heat up.

Keep the car seviced, this is definetely true!Normally I would get 400miles per full tank. Recently, I didnt bother servicing my car when it was due and after about 5000 mile overdue I was getting less than 350 per tank. although saved money not getting serviced it was a 'false economy'.

keep tyre pressure correct, check every 2nd time you fill.

Voodoomelon

stek wrote: »

when parking, reverse into a spot rather than having to reverse out when the engine is cold. Im told this can save up to €100 a year in fuel.

I always do this, but more due to the fact that it reduces engine wear.

szidzio

Hi, i bought bmw 320d 2008 couple months ago. The thing is i am getting only 41mpg , their papers says 49mpg urban, 59mpg mixed and 69mpg motorway, so as u can see my car is rally far of this 59mpg.
Does anybody has similar experience?
I made already 6000 miles witch i think should be enough for engin to start work properly, but who knows?

zilog_jones

Anan1 wrote: »

Lads, i'm lost here. If you take your foot off the accelerator in gear the car will decelerate far more quickly than if you were coasting in neutral. This is because car in gear + no throttle = engine braking. How can this possibly be more fuel-efficient than coasting?

When you're coasting your engine is using fuel to stay at idle speed. However, if you're engine braking the engine is consuming no fuel as an overrun fuel cut-off state occurs - not sure if this applies to all electronic fuel injection systems, but AFAIK most if not all remotely modern engines do this (definately not carburettor systems though).

http://en.wikipedia.org/wiki/Engine_braking (the talk page has some links to overrun fuel cut-off info)

There is the downside of increased drivetrain wear but I'm not sure how significant this is.

kluivert wrote:

9. Fill to the brim, and dont re-fill till the fuel warning light comes on, will give you the MPG average.

This will not give you an accurate calculation, as the warning light could mean there's anything from 0-5 litres of fuel left, or even more depending on the car.

The only somewhat reliable fuel level you have to work with is when the tank is full. So for those without fancy trip computers:
1. Fill your tank
2. Reset your trip counter
3. Then refill the tank to full (whenever), and take down the amount you filled it by from the pump. This is the amount relevant to the distance travelled on your trip counter.

Of course there's a downside to that too as you have to fill the tank, adding weight as others said.

After starting the engine, drive off straight away. Dont wait for the engine to heat up.

+1
It'll heat up much quicker if you are driving, which is better for the engine as the oil will heat up to normal temps quicker, and better for you as you'll be warm!

Anan1

zilog_jones wrote: »

When you're coasting your engine is using fuel to stay at idle speed. However, if you're engine braking the engine is consuming no fuel as an overrun fuel cut-off state occurs - not sure if this applies to all electronic fuel injection systems, but AFAIK most if not all remotely modern engines do this (definately not carburettor systems though).

Sure, but you're also dramatically increasing friction, which is costing you in lost momentum. This has to more than outweigh any savings from not having the engine idling without load, no?

zilog_jones

Yes, but we're trying to slow down (to stop at a junction or go downhill as kluivert originally said) so I'm not sure where the problem lies. If you were coasting in the same situation you would be using fuel and need to use your brakes more, increasing brake wear and creating wasted energy from that friction (unless your car has regerative braking like in a Prius or EffecientDynamics BMWs).

Anan1

zilog_jones wrote: »

Yes, but we're trying to slow down (to stop at a junction or go downhill as kluivert originally said) so I'm not sure where the problem lies. If you were coasting in the same situation you would be using fuel and need to use your brakes more, increasing brake wear and creating wasted energy from that friction (unless your car has regerative braking like in a Prius or EffecientDynamics BMWs).

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.

zilog_jones

Anan1 wrote: »

If the aim is to conserve momentum down a hill, though, you'd be far better off coasting in neutral.

Well it depends how much of a hill you're talking about. You can maintain your speed by engine braking on a serious slope whereas you'd be going too fast and may need to brake if coasting - you don't want to be braking for long periods either (excessive heat, brake fade and all that). Try driving around Cork city - you'll need both types of braking :eek:

The thing I don't like about coasting is that you are not in full control of the vehicle. Also your engine is much more likely to cut out when idling than when in gear - not something you want to happen when you're moving and have power steering, hydraulic brakes and clutch, etc. Of course that's no problem in cars actually designed with coasting in mind, i.e. hybrids and "mild hybrids" that turn off the engine when doing so (I assume they all have electric power steering etc.?).

DublinDilbert

realcam wrote: »

The alternator generates far more electricity than needed for all the stuff in a car. Plus some more to actually charge the battery. So you can play the music as loudly as you like. Anything that runs on the battery/alternator. Doesn't matter with regards to fuel consumption.

Based on your above statement it looks like you've discovered away to generate free energy!

Any electrical load put on the alternator, will cause an increase in torque required to turn the alternator, hence loading the engine and using extra fuel.

The only free energy in a car with an internal combustion engine is heat... in a petrol car 20 -> 30% of the energy put in as fuel ends up as waste heat... so turning the temperature knob up on your heater uses no extra fuel!

pete4130

In all fairness...an 80 litre tank of petrol weighs about 9 stone, so a half tank weights about 4.5 stone...are you really going to save that much wieght by not having an extra 4.5 stone in the car? It's the weight of a small child, 2 or 3 crates of beer, the weekly shopping load, the spare tyre, a beer belly and man boobs...or a slight headwind. If your that concerned, dno't accelerate fast, keep your tyres at the right pressure, your filters clean, drive a little slower, don't brake when you don't need to and take you foot off the accelerator when you anticipate a red light ahead....you'll save far more than having a half tank food.....I think I'll eat half a lunch tomorrow....less body mass to carry around until dinner time so I won't get so hungry......

Voodoomelon

Indeed, but if I do all the things you mentioned, which I do, AND cut 35kg of weight by not filling the tank, i'll save that bit more.

And unlike some, I don't mind visiting the petrol station once a week. What i'd hate more is dropping €100 at once to fill the tank so my car runs less effecient.

kluivert

Cookie_Monster wrote: »

How does this work, surely the engine is using fuel to idle in neutral rather than shutting the injectors down while not under load in gear?

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.

kluivert

zilog_jones wrote: »

Yes, but we're trying to slow down (to stop at a junction or go downhill as kluivert originally said) so I'm not sure where the problem lies. If you were coasting in the same situation you would be using fuel and need to use your brakes more, increasing brake wear and creating wasted energy from that friction (unless your car has regerative braking like in a Prius or EffecientDynamics BMWs).

Am afraid I meant that you would have to use your brakes to eventually stop at the junction lol.

Yes more wear and tear

captainosull

Youd think anyone concerned about saving a few quid fuel by half filling/coasting etc etc would just get the bus and stop whining. Christ almighty ive never read as much purile nonsense before....well not since the where do you put your tax disc holder thread.

Some good technical replys an all but cmon like.....

L1011

captainosull wrote: »

Youd think anyone concerned about saving a few quid fuel by half filling/coasting etc etc would just get the bus and stop whining. Christ almighty ive never read as much purile nonsense before....well not since the where do you put your tax disc holder thread.

Some good technical replys an all but cmon like.....

Theres no bus from my house to my office; or my house to my parents house; or my house to the ground of the football club I support....

captainosull

Oh I see, then you have either of two choices; pay for a cab (which you undoubtedly wont) - or quit whining and pay for your fuel. One tip though, maybe if you skip breakfast too you can save the combined weight of what youve eaten and save another 2, maybe even 3 euros per year.

L1011

Still don't get your point - if there are savings to be made, why wouldn't you try to make them? Some of these, e.g. tyre pressure, can make a massive difference - 10%+ - if done properly.

captainosull

Yep - I fully accept that. But where does one draw the line? Like buying less shopping, losing your spare, coasting, filling when empty etc - like live a little.

MYOB

MYOB wrote: »

Still don't get your point - if there are savings to be made, why wouldn't you try to make them? Some of these, e.g. tyre pressure, can make a massive difference - 10%+ - if done properly.

Boring, too much effort, tiring, pain in the arse etc etc.

That hypermiling lark is boring and some of the techniques are pretty dangerous.

el tel

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.

Did he not do it in an A8 and was the journey not London to Edinburg?

Alun

el tel wrote: »

Did he not do it in an A8 and was the journey not London to Edinburgh?

Yes, and his name wasn't Gerry either