ARTICLE: How to get the maximum Fuel Efficiency

[enHack]

i think after a certain threshold speed it is better to put in neutral. i do that myself but never been able to measure the differential cost.
the logic i think in layman's term would be something like this:
say the engine thrust E + additional thrust due to slope S. then total acceleration is E+S . but you will find your car never achieves the speed that will be otherwise produced by E+S . so part of thrust produced by engine is certainly wasted .
the car doesn't achieve the speed for E+S is for 2 reason.
1. you cannot drive at that speed (while coming down flyover)
2. they dynamics of the car itself . i am not sure about it but seen it practically. i am not sure if applicable to better cars.
when the gear is on other factors of the car limit the speed,something also seems very logical given the coupling of various parts. so the car mechanics might not be able to utilize the full effect of S which is an external force.

[vinaydas]

another way i think in A/T cars to save fuel is..
when in a signal remove your gear from D or any other gear and put it in Neutral..
the load on engine is minimised..
correct me if im wrong.

[null]

Well, I am no hypermiler, but I guess these basic steps certainly ensure a higher milage on my '02 Wagonr in Bangalore:

1. Stay within your optimum Torque RPM limits - Always stay at 1500-2000rpm limit; Even when revving, avoid going beyond 2500rpm. I think my car gives its highest torque around this range. Beyond it, I think it ha a flat torque & doesnt help "too much" in accelerating

2. Stick to your overdrive gear whenever possible - Drive as much as possible in 5th gear (above 1200-1300rpm or 1500rpm without any shuddering feeling, shift to next drive)

3. Lightfooted on your accelerator - Very lightfooted on the gas pedal. I never revv my engine unless I am desperate to overtake someone

4. Smart stopping & starting - I am not very keen to be the first to zoom out at a traffic light, however, I would prefer to the first one in the line so that the road ahead is always free and not clogged with buses/autos/twowheelers like how you face it when u try to sneak past that yellow light(changing over to red) by hoodwinking the cop & feeling very smart about myself.

5. Avoid braking as much as possible - Light foot driving helps here.

6. Free moving wheels - I feel my car's wheel bearings are functioning much better (touch wood) than many other cars in front of me when driving. My car continues to roll on & on even in neutral & go close to them where as they are still accelerating. I have tested this by trying the distance covered in other cars along the same stretch (similar traffic & driving conditions) & I see that my car moves extra distance in neutral at those places.

I used to get 12kmpl in the city. Nowadays, I am going above 14kmpl with these decent driving methods mentioned above.

Seriously, Instead of shifting based on gutfeel or speed, isnt it more meaningful to rely on the RPM to make the gear-shift decision? I have been doing this right from my bike days - RTZ which was the only bike to have a tachometer during those days & pretty happy with this approach in getting better performance. What are your comments on this?

[rrs1951]

Originally Posted by gaurav.28ch

Which would give better FE on slopes - Coasting in highest possible gears without pressing clutch or brakes or coasting downwards in Neutral ?

Coasting downwards in neutral is dangerous and should never be resorted to. Petrol is much cheaper than human life.

[Guna]

Originally Posted by rrs1951

Coasting downwards in neutral is dangerous and should never be resorted to. Petrol is much cheaper than human life.

I think it can also damage the alternator. Can someone confirm if this is true.

[anupmathur]

Originally Posted by Guna

I think it can also damage the alternator. Can someone confirm if this is true.

Coasting downhill is not a safe practice!
The alternator will not suffer damage.
The FE while coasting down in neutral or in gear will be almost the same. When engine braking is being used, no fuel is being injected into the engine.

[Atlblkz06]

Originally Posted by Guna

I think it can also damage the alternator. Can someone confirm if this is true.

Why would it damage the alternator? That makes no sense.

[dashoin]

My 3 pice :

1. Fuel efficiency is hugely dependent on driving style, traffic conditions and distance travelled. These points have been amply explained above.
2. The biggest culprit IMO is the tyre pressure esp in the metros. I try to check the pressure usually once in 15 days. I do not know about others but have had to fill in at leat 3-4 points in all the tyres.

3. Shifting in the neutral while going downhill is a dangerous practice. I gave the same answer to the traffic examiner during my first test for a licence and was failed. The practice is to go downhill in the same gear in which you climbed it.

Rgds

[anupmathur]

Originally Posted by dashoin

The practice is to go downhill in the same gear in which you climbed it.

Ah, therein lies the rub!
Too many people believe that that consumes far tooooo much fuel!!

[Guna]

Originally Posted by Atlblkz06

Why would it damage the alternator? That makes no sense.

I have read that pressing clutch while going a downwhill with engine off can damage the alternator. If that is true, it may be the same case when you put it to neutral and drive through a downhill. But yes the conditions are different as the engine is on.
I am not sure about the explenation though.

[anupmathur]

Originally Posted by Guna

I have read that pressing clutch while going a downwhill with engine off can damage the alternator.

Guna, this is a big no no! All modern cars have power steering and/or power assisted brakes, power assisted clutch etc... Under no circumstances should you be driving/coasting with the engine OFF!!

[mithun]

Originally Posted by Atlblkz06

Why would it damage the alternator? That makes no sense.

You are right. It's not going to damage the alternator in any way(based on my a little knowledge !)

[Guna]

Originally Posted by anupmathur

Guna, this is a big no no! All modern cars have power steering and/or power assisted brakes, power assisted clutch etc... Under no circumstances should you be driving/coasting with the engine OFF!!

Well, not many would be doing this. I have seen some taxi guys doing it occassionally.

[sandeep108]

Not too sure about that. If you check your RPM gauge, it will be at idle speed only, whether in 'd' at standstill with brake pressed or in 'n'. The difference will be negligible.

Originally Posted by vinaydas

another way i think in A/T cars to save fuel is..
when in a signal remove your gear from D or any other gear and put it in Neutral..
the load on engine is minimised..
correct me if im wrong.

[blacmagic]

apologies if this specific topic has been covered elsewhere.
I remember a jingle in DD from my childhood that said a lot about fuel saving. one of the things it said was "gaadi kabhi start na rakhe 2 minute se zyada, jhatpat gaadi start ho jaye isme hai munafa". that was way back in the age of the carburettor. it meant that the amount of fuel it takes to start a stopped engine = 2 minutes of idling fuel.
recently, I read on Hypermilers else that an average MPFI engine takes 7 seconds worth idle fuel for the same operation and hence, anywhere you think you will stop for more than 7 seconds, turn your engine off. this was clearly intended for American cars.

what is this figure like for Indian cars? especially in my case, the OHC? I turn off my car at most signals. are these stop/start cycles detrimental to the life of the engine?