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Old 22nd April 2010, 12:46   #16
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Here is my two bits.

Fuel taks are vented to the atmosphere. And more empty space in the tanks means more of the fuel is in vapor state. in hot sun the fuel expands, vapor expands more .
this will push some fuel vapor out to the atmosphere cause of the venting in order to prevent a pressure buildup in the tank. If there is less empty space less fuel is in vapor state and thus less loss.

This is what i guess happens. Tho there may be other forces at play too.
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Old 22nd April 2010, 12:58   #17
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I have always wondered about this, because I have always felt the performance of a car to be better on a full tank, and yet logic tells me that it should not be, because the car is carrying more weight. In fact, I have known a number of people say they never fill the tank full, because why pay for carrying extra petrol around!

Also, in these days of complex fuel injection systems, I would doubt that any additional pressure from the level of fuel in the tank would be of any relevance by the time the fuel mixture enters the cylinder.

However much I talk myslef out of it, though, I still get that full-tank better-car feeling!
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Old 22nd April 2010, 14:16   #18
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Quote:
Originally Posted by aargee View Post
1. The needle comes to half mark after a very long drive, but from half to empty its faster.
Hey nice thread at I too started thinking on this line. Now don't know it's a fact or just my mind diverted but I too agree about above point. Now need to notice about the smoothness in gear shift and pick up. Let me experience it & update what I find.
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Old 22nd April 2010, 14:20   #19
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I have also noticed the same in my car as well as bike.

After refueling, the pick up increases, engine becomes smoother and gears also become smoother.

Earlier I used to think that it may be happening because we generally check tyre pressure also when we go for refueling. But I have felt the difference even when tyre pressure was not changed after refueling.

It can't be just our imagination. There has to be some logical explanation for it.

Rohan
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Old 22nd April 2010, 15:02   #20
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+1 from a santro owner. until i saw and read this thread i always thought its only enough fuel in my mind making me think so.

just did a tank full a few hours back and on way back i had this felling again, if it really happens, i am glad.

lastly my car filters are cleaned very recently and this is not just a imagination that gives a smoother drive.

should i write to "how stuff works" ?
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Old 22nd April 2010, 15:22   #21
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Quote:
Originally Posted by ghpk View Post
+1 from a santro owner. until i saw and read this thread i always thought its only enough fuel in my mind making me think so.

just did a tank full a few hours back and on way back i had this felling again, if it really happens, i am glad.

lastly my car filters are cleaned very recently and this is not just a imagination that gives a smoother drive.

should i write to "how stuff works" ?
But, I had a different observation on my Santro earlier. When ever I filled to brim Engine used to roar and once the fuel is less than half engines goes quite. Was not sure why, But now I see you guys actually are feeling the other way
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Old 22nd April 2010, 15:27   #22
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Should be interesting to see if the car behaves better by rigging the fuel indicator and telling the person the tank is full when its not.
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Old 22nd April 2010, 15:35   #23
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Haven't noticed this difference in my car,
but my Honda Activa starts with just one press of the ignition key when the petrol tank is full, even if parked without using for 3 days.

But it takes atleast 3 or 4 key presses if tank is less than half capacity.
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Old 22nd April 2010, 15:35   #24
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Actually when filled to the brim, the pick up is obviously going to come down becos of the extra weight & I guess with the fuel splashing around in the tank it will slow down the vehicle.

Maruti cars like esteem, zen, baleno have better pickup with just 4-6 litres in the tank & that's the reason cars run light on the track.
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Old 22nd April 2010, 15:57   #25
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I also felt the same on my bike. Maybe it is due to the pressure that a full tank has on the petrol supply. The more the pressure, the faster (maybe easier) would be the petrol flow. Though couldn't really figure out why the gearshift was better with full tank.
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Old 22nd April 2010, 16:59   #26
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The only thing which i have noticed is--the vehicle becomes smoother,

^^the car should return less FE with tankful due to increase in weight(however minuscule the weight increase maybe)
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Old 22nd April 2010, 19:25   #27
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Wow. Guys all your fuel tanks are contaminated. You feel an increase in the pickup with tank full because you are feeding the engine fresh fuel without much contamination. Hence the engine delivers optimum power and is smooth. Once the fuel level starts to go down the percentage of contamination increases and the engine starts to get sluggish. This is because the fuel is not ultraclean and nor the tanks holding them in the fuel station. Over a period of tome, sedimentation takes place and the tank at the bottom gets dirty. Get your car's tank flushed and you will not face this problem.
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Old 22nd April 2010, 19:44   #28
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Quote:
Originally Posted by greenhorn View Post
I'm not sure if my mind is playing tricks on me, but Recently I've noticed that my pickup improves drastically after I tank up.
Got a G-tech? iPhone / iPod touch w/ accelerometer software?

Would be interesting if there was some sort of more solid indication of a difference.

Anyone?

cya
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Old 22nd April 2010, 20:59   #29
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Its probably mind games! Suction would always do the trick and most cars these days have the tank underneath. And whats the fuel pump for? Half a tank should be better than a full tank from what I've seen.
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Old 22nd April 2010, 21:47   #30
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Quote:
Originally Posted by Rehaan View Post
Got a G-tech? iPhone / iPod touch w/ accelerometer software?

Would be interesting if there was some sort of more solid indication of a difference.

Anyone?

cya
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Rehaan, you're a geeky nerdy spoilsport . Your insistence on facts and figures/ instrumented tests is going to take the fun out of such interesting threads!

Regards
Sutripta
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