[fast lane]

Mostly its said "do not ride the clutch" by which I understand that partial depression of clutch is harmful.

Kindly advice on FULL DEPRESSION of clutch at small slopes or while rolling up to a toll booth or a signal.

Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?

How will the FE be affected?

Soumo Chatterjee

[deadguy25]

Originally Posted by fast lane

Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?

How will the FE be affected?

Soumo Chatterjee

When you say "depress", if you mean by pressing the clutch fully, then it is wrong. All you need to do is take your foot of the throttle, unless you want to slow down quickly.

[ImmortalZ]

Originally Posted by fast lane

Mostly its said "do not ride the clutch" by which I understand that partial depression of clutch is harmful.

Kindly advice on FULL DEPRESSION of clutch at small slopes or while rolling up to a toll booth or a signal.

Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?

How will the FE be affected?

Soumo Chatterjee

You will get less mileage if you depress the clutch and let the car roll freely compared to just letting the accelerator go. This is because modern cars with electronic fuel injection (even the humble 800) use no fuel at all when they are coasting with the transmission locked to the engine. Press the clutch and the engine will start consuming fuel to keep it running (idle running).

It is also a dangerous practice as you'll lose the advantage of engine breaking in case you need to hit the brakes suddenly.

[akroy]

Originally Posted by fast lane

Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?

What has clutch to do with the speed? If you need to slow down apply your brakes and not the clutch. Only then engine braking plus your pedal braking both with assist the car to slow down efficiently and you will be more in control.
If you simply want to reduce the speed, dont press the accelerator, engine braking will slowly reduce the speed to your desired level.

Use clutch only to change gears and yes, press fully to do so.

Abhi

[jat]

Originally Posted by fast lane

.........Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?...Soumo Chatterjee

Clutch has got the function for changing gears only. And at that time, it has to be either fully depressed and normal time, your foot should be off it. Also when stopping, use the clutch to prevent the engine from stalling, when applying brake.

For speed control, accelerator or combination of accelerator and brake to be used.

[aka_iitd]

Some info
Maruti Publishes Fuel Efficiency Figures!
Link
Maruti_Publishes_Fuel_Efficiency_Figures!

[vasudeva]

I have noticed one thing in the extreme Delhi weather. Average FE is lowest in monsoons (traffic jams, etc), increases in winters but is the highest in Feb-Apr. Is it because of the cold conditions in Delhi right now.

[Guna]

Originally Posted by fast lane

Also if the car has attained a speed of 100 KMPH, is it advisable to depress the clutch fully till say the speed has dropped down to 80 KMPH and then accelerate slowly again to 100?

Your car may break free instead of slowing down, if you keep the clutch depressed at 100, unless you are approaching a uphill.
Best way would be to either lift off or gently press the brake

[hoomdo]

Originally Posted by vasudeva

I have noticed one thing in the extreme Delhi weather. Average FE is lowest in monsoons (traffic jams, etc), increases in winters but is the highest in Feb-Apr. Is it because of the cold conditions in Delhi right now.

@Vasudeva
Excuse me for trying to "advise" a senior BHPian (i am already intimidated ) but I believe the FE goes up in Feb-Apr because of the below two factors:

1) No AC (at least till March) - hence higher FE than summer.

2) Even though its no AC in Dec-Jan too, bu the chill means that more fuel is burnt to achieve the same temperature. (taking the analog of bringing water to boiling temp consumes more fuel in winter). Hence. FE in Dec-Jan will be lower than Feb-Mar.

Am I right?

[Atlblkz06]

Originally Posted by hoomdo

2) Even though its no AC in Dec-Jan too, bu the chill means that more fuel is burnt to achieve the same temperature. (taking the analog of bringing water to boiling temp consumes more fuel in winter). Hence. FE in Dec-Jan will be lower than Feb-Mar.
Am I right?

Engines do not burn extra fuel just to maintain their temperature. Our engines are so inefficient they inherently overheat and require large amounts of cooling.

If the engine isn't hot, the thermostat does not open too wide and the cooling system simply deactivates to maintain operating temperature.

It takes temperatures well below 0C to affect the engine in ways you describe.

[GTO]

To add to what Atlblkz06 posted, I find my engines running much better in the winter as well. True cold-air-intake season!

[Jeep]

Theoretically, the max efficiency of an engine is 1 - Temp of Sink/Temp of Source.

Source =
Temp of source (inside engine) reaches the max after sometime (then the thermostat functions and radiator fan is switched on). Hence, whether it is winter or summer, we can assume that the temp inside the engine is the same.

Sink = Outside environment. Hence, the drop in ambient temp will result in a marginal increase in the efficiency

Note: The temperatures mentioned above are absolute (in Kelvin), so the impact is minimal with the changes in atmospheric temp which are not large as compared to the readings if read in Centigrade

[Atlblkz06]

Originally Posted by vasudeva

I have noticed one thing in the extreme Delhi weather. Average FE is lowest in monsoons (traffic jams, etc), increases in winters but is the highest in Feb-Apr. Is it because of the cold conditions in Delhi right now.

You'll find big gains in power in winter from a cooler air charge as well as better intercooling and engine cooling. I'm not surprised to see that your economy is higher. Also remember that A/C usage decrease your mileage slightly.

I've found that rain and wet roads can have a significant impact on mileage (Pure highway driving at 70mph - I noticed a 10% drop). When you're driving along at a constant speed and hit a patch of water, you can immediately feel the drag from the water. My theory is that driving on wet roads provides a "constant drag" on the tires that lowers your mileage. As you pointed out - city traffic is always a mess when it rains which doesn't help either.

[hoomdo]

Originally Posted by Atlblkz06

You'll find big gains in power in winter from a cooler air charge as well as better intercooling and engine cooling. I'm not surprised to see that your economy is higher. Also remember that A/C usage decrease your mileage slightly.

I've found that rain and wet roads can have a significant impact on mileage (Pure highway driving at 70mph - I noticed a 10% drop). When you're driving along at a constant speed and hit a patch of water, you can immediately feel the drag from the water. My theory is that driving on wet roads provides a "constant drag" on the tires that lowers your mileage. As you pointed out - city traffic is always a mess when it rains which doesn't help either.

Sound logic @ Atlblkz - but then how can we explain the higher fuel efficiency (as reported by vasudeva) in Feb-Apr than Dec-Jan? I had taken the simple assumption that in the scenario, of thermal energy converting to mechanical, less loss due to higher atmospheric temp helps. Apparently i am wrong - but then what hits the FE in Dec-Jan?

[Atlblkz06]

Originally Posted by hoomdo

Sound logic @ Atlblkz - but then how can we explain the higher fuel efficiency (as reported by vasudeva) in Feb-Apr than Dec-Jan? I had taken the simple assumption that in the scenario, of thermal energy converting to mechanical, less loss due to higher atmospheric temp helps. Apparently i am wrong - but then what hits the FE in Dec-Jan?

His wife's birthday is in December their anniversary is in January. Every year he keeps forgetting and he has to rush to the store to buy her a gift. Of course if he goes nearby, she'll know since she has all the items memorized. So he has to drive an extra 50 miles or so to pretend to have planned the purchase. Now he doesn't want to admit this extra driving to us so hes just complaining that his mileage isnt as good.

Hows that for an explanation?

But seriously - I dont know. When is the monsoon season in India?

Maybe seasonal changes in fuel? I know here in the states they switch to a less efficient cold-weather-friendly blend in winter. (Or is summer fuel less efficient?)