[ph03n!x]

Originally Posted by Fountainheader

The other day I was at Shell Poonamallee and as usual I asked them to top it up. Generally I stop at auto-cutoff unless I'm going on a highway drive, where I ask him to full to the brim.

So that day, somehow while the attendant was cleaning the windscreen, petrol overflowed out of the water tank. Not sure how much qty spilled out, I got a discount of around 60 bucks.

What I want to know is that if the attendants are responsible for the auto cutoff ? Or is there something wrong with my car ?

Water Tank?!!!

Most modern pumps have an auto cut-off feature that stops the flow of fuel once the tank is full. This is done by having a second tube, the sensing tube, that runs from just inside the mouth of the nozzle up to a Venturi pump in the pump handle. While the tank is being filled, air displaced from the tank is drawn up this tube. Once the fuel level reaches the mouth of the sensing tube, air is no longer drawn up the sensing line. A mechanical valve in the pump handle detects this change of pressure and closes, preventing the flow of fuel.

Source

Don't think anything is wrong with the car. Not really sure if the fuel attendant will be penalized for something beyond his/ her control- the dispenser is supposed to stop!

[gpa]

Originally Posted by Fountainheader

What I want to know is that if the attendants are responsible for the auto cutoff ? Or is there something wrong with my car ?

Fountainheader,

There is nothing worng with your car. The auto cut-off mechanism is built into the fuel gun which could have malfunctioned.

Cheers,
gpa

[Abhi_rx]

When i'm topping up fuel for my Dzire, i notice that the Diesel tends to overflow suddenly. This happens even when the tank is half empty so its necessarily not an Auto cut off. The attendants say its because of excess air in the fuel tank. There is no problem when fueling slowly, but if the attendant sets the mode to fast i can be sure there will be overflowing. Now this is becoming a problem since my drives are normally on the highway and my fueling up habits are full-empty. Every time i drive into a fuel station I have to politely ask the attendant to fuel up very slowly, some take it well others become irritated with the thought of having to bend and hold the fuel nozzle for 30+ liters that too in slow mode.

Can somebody suggest a permanent remedy for this please?

[Jaggu]

Nothing much you can do about this, try to convince them to fill fuel slowly OR atleast slow down near to the point when the tank would get full (approximate liters you think it will take).

[vsathyap]

IMHO How you drive matters more in terms of FE rather than getting an early morning fill -up. The difference in quantity is hardly 36ml (I did this calculation on a website that had very scientific calculations WRT the exact same topic - they stated that the coefficient of expansion of Gasoline is so little that temperature changes of even 20 deg C really didnt make that much of a difference).

Driving in the right gear and reducing unnecessary racing and braking will improve your FE significantly.. I dont believe in early morning fill-ups :P

[Gansan]

Originally Posted by vsathyap

IMHO How you drive matters more in terms of FE rather than getting an early morning fill -up. The difference in quantity is hardly 36ml (I did this calculation on a website that had very scientific calculations WRT the exact same topic - they stated that the coefficient of expansion of Gasoline is so little that temperature changes of even 20 deg C really didnt make that much of a difference).

Is that per litre? Then are we not talking of ~ 1.25 litre per tankful?

I always top-up when my tank reaches the half way mark. And I always do it in the morning!

[Aroy]

A liter will always be a liter, whether on a cool morning, or torrid afternoon. The weight will differ with temparature.

One advantage of filling when it is cool, is that less vapour forms, hence there is less back pressure. One thing puzzles me - there is normally a thin return pipe whose main job is to prevent a vapour back pressure, keeping it clean will ensure that fuel does not spill out prematurely while filling.

I normally fill when the petrol indicator starts blinking in my Alto K10, or just about touches "E" on my Esteem. Till date I have never had problems with dirty fuel or clogged fuel lines. I guess dry Delhi climate keeps the rust in abeyance.

[sachinj12]

Originally Posted by Abhi_rx

When i'm topping up fuel for my Dzire, i notice that the Diesel tends to overflow suddenly. This happens even when the tank is half empty so its necessarily not an Auto cut off. The attendants say its because of excess air in the fuel tank. There is no problem when fueling slowly, but if the attendant sets the mode to fast i can be sure there will be overflowing. Now this is becoming a problem since my drives are normally on the highway and my fueling up habits are full-empty. Every time i drive into a fuel station I have to politely ask the attendant to fuel up very slowly, some take it well others become irritated with the thought of having to bend and hold the fuel nozzle for 30+ liters that too in slow mode.

Can somebody suggest a permanent remedy for this please?

Never experienced this in my 2 years of ownership. 9 out of 10 times, I always do a full tank. And I don't ask the attendant to slow fill. He just fills it as he does normally.

[mgh]

Coefficients of expansion are 0.00095 for petrol and 0.00082 for diesel. 10 deg C change in temperature will change volume by 0.95 % for petrol and by 0.82 % for Diesel. Plus underground temperatures vary much less than the ambient air temperature. Once you are approximately 30 ft below ground, the temperature is almost constant at a given place.
In principle, you save by buying fuel early in the morning. Don't think anyone will ever be able to prove it, as FE variations due to other causes are much more. It serves as a placebo, nothing more.

[govigov]

Originally Posted by vsathyap

IMHO How you drive matters more in terms of FE rather than getting an early morning fill -up. The difference in quantity is hardly 36ml (I did this calculation on a website that had very scientific calculations WRT the exact same topic - they stated that the coefficient of expansion of Gasoline is so little that temperature changes of even 20 deg C really didnt make that much of a difference).

Driving in the right gear and reducing unnecessary racing and braking will improve your FE significantly.. I dont believe in early morning fill-ups :P

36 ml for how many liters? 50L or 100L or is per liter?

[vsathyap]

Originally Posted by govigov

36 ml for how many liters? 50L or 100L or is per liter?

That is for a tank full ...assuming a capacity of 50l. The reason being that the temperature of gasoline hardly varies by about 5 deg c in the underground tanks that store it in filling stations.

[FlatOut]

anjan_c2007 and vsathyap have it right - maintaining a fuel tank more than half full just to minimise losing fuel through evaporation is crazy. Unless you own a 2 tonne car with a 50 litre tank, constantly acclerating the extra mass will far outweigh the loss of fuel through evaporation. And anyway, don't more recent cars prevent evaporation out of the car? - I thought that's what the carbon capture cans are for.

As an aside, if you have your own fuel supply then there is good evidence to suggest a warmer fuel temperature will give better fuel economy, up to a point. Given the relatively low temperature variations in a massive tank of fuel which sits underground, the idea of filling your car early in the morning is verging on obsessive compulsive disorder! Choose a quality brand from a source you know you can trust for clean and water-free fuel. And don't drive around a city all day with a nearly-full tank, you may as well be pulling a trailer with the effect it has on economy.

[condor]

It's been a long time since I read the posts in this thread. So I will post this, at the risk of duplication by any one else.

Best time to fill ? Morning / late evening. You will get more fuel in.

No, it's not the fuel at the bunk. The tanks in the bunk are well inside, and are not that much affected by external temperature. It's our vehicles.

The fuel tanks of our vehicles are exposed to ambient temperature. Hence on a hot day, fhe fuel will expand and use up a little more space in the tank. Hence we will be able to get less fuel in into the tank.

[Gansan]

Originally Posted by FlatOut

And don't drive around a city all day with a nearly-full tank, you may as well be pulling a trailer with the effect it has on economy.

Are you serious? How much extra fuel are we talking about here? My car has a 35 litre tank, so the fuel can't weigh more than 35 kg. The weight of a kid! And the car mostly has only one or two occupants! Even a fifty litre tank will not matter that much!