[mayankk]

yes it does.releases the air pockets, if any.
sort of like shaking a container of "dal" after its been filled, but accmodates to a much lesser extent.
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[thedreamcatcher]

I certainly dont think it will accomodate to the extent of one litre more. Generally, there is a lot of air, which takes up space and a bit of air gets pumped in during the fueling process as well

Hence by shaking the car, we are actually letting air come out

Now, one important thing to understand is, it is not about more fuel going in. If that happens, we would end up paying more for shaking the car then ;-). It is just removing the air bubbles, and can also result in a more accurate fuel guage reading. How much fuel goes in is already predetermined. Say 10 litres, the whole 10 litres goes in either ways, and just because there is air, does not mean only 9 go in or if I shake the car, 11 goes in. No way.

The benefit of this is more evident when you go for a tank up. So if you have a tank capacity of 45 litres, with air in it, you may only be able to tank up to say 44.5. By shaking and realeasing air, you can take in a bit more

The Skoda Fabia has an air release valve situated in the fueling area, for this very purpose

[rideon]

Originally Posted by mayankk

yes it does.releases the air pockets, if any.
sort of like shaking a container of "dal" after its been filled, but accmodates to a much lesser extent.
qualified for a thread?
cheerios!

I think "dal" being solid, it is but natural for air to fill up in places. But then with liquid, and that too with fuel level rising in the tank, I fail to understand where the air pockets would be. Air would anyway be pushed out.
My understanding for the shaking is to determine the level of fuel in the tank after auto-cut from a visibility perspective.

[VW2010]

....understand where the air pockets would be. Air would anyway be pushed out.......

Its the shape of the tank that creates the air pockets that will not move out of the tank by mere filling of the tank. The shake just displaces the air pocket to move towards the mouth for easy release through the mouth.

Try filling a 5 L can with water and you will understand there will be Air Pockets in the handle no matter how hard you force the water into it. But by just tapping the can and slowly moving the air pocket one can fill a little more.

[SS-Traveller]

Never thought anyone would ask!!!

What it does:
Shaking does accommodate a little more fuel (around 1-2 litres) in most cars, by eliminating an air pocket right at the top of the tank. This air pocket is also where an air vent is located in newer design tanks, to accommodate expansion of fuel. So, when you shake the car to top up right up to the filler neck, some part of that fuel is likely to dribble out from the vent and be lost.

Why people do it:
This is a genetic programming coded into taxi drivers who/whose trainers learnt about cars through driving the Amby. The Amby tank was notorious for having an air space that could accommodate upto 3-4 litres of extra fuel, and there was no air vent to make it spill out. In fact, the filler hole was placed on top of the tank in the old Ambys, and filling to the neck meant there was fuel in the filler pipe too, which connected the tank to the filler hole. The filler cap was the air vent, and a new lock-less design of cap fitted by HM sealed so well that there used to be air locks and fuel flow to engine cut off on long runs (I've suffered it).

Taxiwallahs continue to indulge in this practice for another reason. Under certain types of owner-driver contracts, when they are allotted a car, they are paid to fill up the car to the max., which they do. When they return the car for the night, they are expected to bring in a full tank as well as pay the owner for the number of km run - at this time they fill a little short, and though the fuel gauge might show a full tank, he's still saved the money for about 5 litres of fuel. The cycle repeats itself with a new driver, in case the fuel gauge shows less than full, a few days later. The next day's driver doesn't get the benefit of topping up to the brim, or in case the car is sent out on a short run only.

What you should do:
Forget this technique. Fill up to the point where the dispenser auto-trips, and round off to the nearest Rupee denomination if required. Auto-cut to overflow can be around 2 litres of fuel, and you can be sure to waste at least 500ml due to fuel dribbling out if you shake and fill.

Edit:

Originally Posted by thedreamcatcher

The Skoda Fabia has an air release valve situated in the fueling area, for this very purpose

All cars built in the last decade do. The vent is spring loaded, and will only release air under pressure (when expansion takes place), or let in air when partial vacuum forms in the tank. However, filling fuel upto the point where the liquid comes in contact with the vent means it will allow some of the fuel to trickle out.

[mdsaab]

Ok. I have to admit it. I have done this before. But not much fuel goes in after shaking. So i just let it fill till auto fill, and then round it up. I guess this technique of shaking is followed more by the highway kings. if you are going to be driving around within the city, what difference is an extra litre or two going to make. You would probably still end up at the pump the the same day with or without 1-2 litres.

[anku94]

Doesn't exactly relate to shaking up a car, but what are the consequences of forcing the fuel in the car after the auto cutoff state has been achieved ?

We live in Punjab, and we had to go to Chandigarh for a day, where the fuel is 6-7 rupees cheaper. We were driving on an almost empty tank, and while in Chandigarh, my dad made the guy at the pump fill 40 litres, although the cutoff state had been reached at 32 litres.

[libranof1987]

Originally Posted by thedreamcatcher

The benefit of this is more evident when you go for a tank up. So if you have a tank capacity of 45 litres, with air in it, you may only be able to tank up to say 44.5. By shaking and realeasing air, you can take in a bit more

If this were the case, wouldn't it help shaking the car BEFORE filling fuel rather than after auto cut-off?

Originally Posted by SS-Traveller

So, when you shake the car to top up right up to the filler neck, some part of that fuel is likely to dribble out from the vent and be lost.

Where exactly does the excess fuel trickle out from?

Originally Posted by anku94

We were driving on an almost empty tank, and while in Chandigarh, my dad made the guy at the pump fill 40 litres, although the cutoff state had been reached at 32 litres.

A diff. of 8 litres?! Guess the guy was cheating you till the time he reached 32l.

[VCheng]

The volume of dead space is more than just air bubbles. There are evaporative control canisters and associated piping as well.

For example, this dead space can mean an additional 17.5 liters (approx) after initial fuel cut-off in a US spec LX470 to about 9.5 liters in a US spec Corolla.

[dhanushs]

Originally Posted by SS-Traveller

The Amby tank was notorious for having an air space that could accommodate upto 3-4 litres of extra fuel

+1 . Yes, I believe it was the taxi drivers of the Amby's that really started this whole thing.

Originally Posted by libranof1987

If this were the case, wouldn't it help shaking the car BEFORE filling fuel rather than after auto cut-off?

The whole point of shaking the car AFTER filling is to release trapped air pockets, and hence be able to fill more fuel.

Obviously, shaking is practiced only while you tank up, or else, there would be only ONE air pocket in an empty/partially empty tank, which of course is quite difficult to remove by just shaking.

Originally Posted by libranof1987

A diff. of 8 litres?! Guess the guy was cheating you till the time he reached 32l.

Well, sometimes in some pumps, after the 1st cut off, even without shaking, the car will easily take in 4-5 liters till full tank(not brim).

[mail4loys]

Originally Posted by anku94

We were driving on an almost empty tank, and while in Chandigarh, my dad made the guy at the pump fill 40 litres, although the cutoff state had been reached at 32 litres.

Originally Posted by dhanushs

Well, sometimes in some pumps, after the 1st cut off, even without shaking, the car will easily take in 4-5 liters till full tank(not brim).

I have seen that my Ikon takes ~10 + lts of petrol after the first cut off. I have seen this in all company petrol bunks. I let the attendant know that it can take 10 more liters and ask him to fill slowly.

[n.devdath]

Even the Scorpio accomodates around 2.5-3 liters of fuel if I shake it well after the auto cut off. I always shake it and have had no spillage or reduced FE due to this.

[Gansan]

My Alto will take in 1 to 1.5 litres of fuel after auto cut off, for a brimful.

[anku94]

Originally Posted by libranof1987

A diff. of 8 litres?! Guess the guy was cheating you till the time he reached 32l.

I doubt that. When we went to Ambala one other time, my dad did the same and got similar quantity of fuel filled.

Now that we have other members reporting similar 'capabilities' of their rides, I'm pretty sure that no cheating was involved.

The question is, is this a safe/useful thing to do ?

[qqplus]

Hi,

Well,
As I could read in most of the responses, shaking DOES result in more fuel finding place in your fuel tank.

I debated on this point with an engineer, who stressed that air pockets cannot be trapped in fuel tank like that; whereas in case of daal they can and they do.

That is why this question. I guess I have to debate further on this point.

Thanks

Apurva