Freewheeling to save money

The car is pretty old so I don't think it has the cut off thing.

Exactly how 'old' do you think 'old' is?

mad_rich wrote: »

Because the engine needs to turn at ~1000 rpm to idle.

If the car is in neutral (or the clutch is down) it does this by merrily combusting and using fuel.

If you are in gear, with your feet off all the pedals, the road wheels are turning the engine via the transmission, hence no fuel is needed.

The downside is that you'll have engine braking, so your run will be shorter than if you were out of gear.

If your in gear with your feet off the pedals, the engine will instantly absorb your momentum through engine braking, from that point on you will require drive from the engine to maintain movement, unelss ofcourse your travelling down a hill i supose

Just to be clear i agree totally that coasting is not a good idea and probably of little or no benefit in terms of saving fuel, but i cant imagine how it would increase your fuel consumption

Limey wrote: »

For petrol engines the mid to late 80s approximately, not sure about diseasals.

Fuel cut when the throttle is off was later than that, probably early to mid 90s.

Diesel engines have been using them since they were invented!

Just to be clear i agree totally that coasting is not a good idea and probably of little or no benefit in terms of saving fuel, but i can't imagine how it would increase your fuel consumption

On a modern fuel-injected engine [post early-mid 1990's, if Skodas are anything to go by?}...when the throttle is closed [ie, off the as, but still in gear....over-run?]....the TPS registers that fact, tells the ECU , which returns all fuel back to the tank...meaning, the injectors are shut.

Thus, no fuel used.

SO, if I'm driving along in my Fiesta, or Felicia, at 60mph, in 5th gear....and I come off the gas, I'm not burning any fuel. {from 60mph, on a level road, it currently takes my Fiesta zetec more than half a mile for the speed to drop down to around 30mph in 5th.]...during this time, no fuel is being used.

On the Fiesta Zetec, the ECU detects when the engine revs have fallen below around 1500 rpm {?} when it opens the injectors again, and starts to burn fuel.....this it does when the engine is at tickover...to keep t running. [tickover typically around 7-800 rpm approx]..

The Felicia mpi did similar...although the top rev point for fuelling was lower than the Fiestas [approx 1100 rpm as against 1500 rpm].....in my experience.

Thus, if [with cars newer than 20 years old]....one simply either depresses the clutch pedal, or puts the gearbox into neutral gear, at speed [coasting or free-wheeling]...the engine is at tickover revs, therefore will be burning fuel to keep itself running.

Thus, will use more fuel than simply 'coming off the gas'..

Thus, if one is travelling along quite quickly, and one either can 'see'...or knows about, a speed reduction need ahead, one can save fuel by coming off the gas early, and allowing the vehicles speed to fall off naturally, without using hte brakes!

Thus, the longer one is on over-run, the more fuel is saved.


This can be confirmed on many credible websites such as AA, RAC, IAM, and other such worthies......google 'economical driving techniques?'


Now, for an older generation driver the above is quite the contrary to accepted opinion for economical driving in a car with carburettor.

With carbs, there is no real 'sut-off' of the fuel......regardless of whether the throttle is open or closed.

Thus, at tickover, the engine uses less fuel than on the over-run....so 'coasting' was a valid, if unsuitable, thing to do, to save fuel.


For a direct personal example, I offer the Skoda comparison.....

I have [had] two different types of Skoda, but both using the same basic [136] engine.

One [in a Rapid] uses a carburetor...the other [a Felicia] uses ECU-controlled fuel injection.

[To be even fairer, the Rapid engine is equipped, by me, with a Felicia cylinder head, and electronic ignition, so is identical apart from the fuel injection system]...


With my normal driving style, the Rapid barely achieves 35 mpg....the Felicia achieves 49 mpg...and the Felica is a heavier car too.

Such are the advantages of an electronically-controlled fuelling system?

alastairq wrote: »

On a modern fuel-injected engine [post early-mid 1990's, if Skodas are anything to go by?}...when the throttle is closed [ie, off the as, but still in gear....over-run?]....the TPS registers that fact, tells the ECU , which returns all fuel back to the tank...meaning, the injectors are shut.

Thus, no fuel used.

SO, if I'm driving along in my Fiesta, or Felicia, at 60mph, in 5th gear....and I come off the gas, I'm not burning any fuel. {from 60mph, on a level road, it currently takes my Fiesta zetec more than half a mile for the speed to drop down to around 30mph in 5th.]...during this time, no fuel is being used.

On the Fiesta Zetec, the ECU detects when the engine revs have fallen below around 1500 rpm {?} when it opens the injectors again, and starts to burn fuel.....this it does when the engine is at tickover...to keep t running. [tickover typically around 7-800 rpm approx]..

The Felicia mpi did similar...although the top rev point for fuelling was lower than the Fiestas [approx 1100 rpm as against 1500 rpm].....in my experience.

Thus, if [with cars newer than 20 years old]....one simply either depresses the clutch pedal, or puts the gearbox into neutral gear, at speed [coasting or free-wheeling]...the engine is at tickover revs, therefore will be burning fuel to keep itself running.

Thus, will use more fuel than simply 'coming off the gas'..

Thus, if one is travelling along quite quickly, and one either can 'see'...or knows about, a speed reduction need ahead, one can save fuel by coming off the gas early, and allowing the vehicles speed to fall off naturally, without using hte brakes!

Thus, the longer one is on over-run, the more fuel is saved.


This can be confirmed on many credible websites such as AA, RAC, IAM, and other such worthies......google 'economical driving techniques?'


Now, for an older generation driver the above is quite the contrary to accepted opinion for economical driving in a car with carburettor.

With carbs, there is no real 'sut-off' of the fuel......regardless of whether the throttle is open or closed.

Thus, at tickover, the engine uses less fuel than on the over-run....so 'coasting' was a valid, if unsuitable, thing to do, to save fuel.


For a direct personal example, I offer the Skoda comparison.....

I have [had] two different types of Skoda, but both using the same basic [136] engine.

One [in a Rapid] uses a carburetor...the other [a Felicia] uses ECU-controlled fuel injection.

[To be even fairer, the Rapid engine is equipped, by me, with a Felicia cylinder head, and electronic ignition, so is identical apart from the fuel injection system]...


With my normal driving style, the Rapid barely achieves 35 mpg....the Felicia achieves 49 mpg...and the Felica is a heavier car too.

Such are the advantages of an electronically-controlled fuelling system?

I guess i shouldn't have decided to become a Bus Driver after all