Petrol mystery?

[Spanish S2]

Hi all, filled S up with petrol yesterday and went for a run everything O K. Today, strong smell of petrol walking past the car, opened up cap, petrol to top of pipe and leaking out of overflow? Is this as daft as it sound's?

[techbotics]

Did you brim it? Ie really full.. Fuel cold in uh tanks then expands.? Assume journey home not too far? And been relatively warm today.

That's all I have... Hmm..

Damian S3

[glenrobbo]

Two possible explanations:

1. Your run was far too short.

2. Your S is so environmentally friendly.that it has started generating its own petrol. Cherish it & drive it all you can.

3. ( !?!? ) A large Murcian hydro-carbon loving reptile has taken up residence in your fuel tank & displaced an amount of fuel equivalent to its own weight.*
Call him Archimedes & take him out for plenty of long drives.

HTH
Glen

Edit : * Not strictly true, he would actually have experienced an upthrust equal to the weight of fluid displaced. If he's real.

On reflection, a better name for him would be "Eureka", don't you think?

Edited by glenrobbo on Saturday 2nd November 19:14

[lewdon]

Not as good as the brilliant answer above - but I think Techbotics is right

Petrol coefficient of expansion = 0.000950 / (C or K)

so for (say) a 15 degree (C or K) temperature rise

ΔV = V0βΔT

ΔV = (1 litre)(0.000950)(15)

ΔV = 0.01425 litres

so approximately 1% more petrol for every 10degC rise in temp.

if it was a very hot day probably equivalent to adding nearly an additional litre to the tank.
(but you must have really filled it the brim)

[glenrobbo]

Serious answer now ,
Allied to the temp / pressure / expansion hypothesis.
The rectangular slab- sided fuel tanks of S's are prone to flexing ( it's called "panting" ) under certain conditions. Think of Rolf Harris' Wobbleboard or pressing the top of an oil drum that has a slight convex bow in it.
This could displace a volume of petrol in addition to the thermal expansion.

Simples.

Footnote: I could go into the relevant scientific formulae, but my phone doesn't do Greek.
It often lapses into Double Dutch though.
( No offence Han )

Edited by glenrobbo on Saturday 2nd November 19:30

[S2Mike]

Just my two euros worth ! Is there a chance something may have impacted the underside of the tank, causing a dent reducing the capacity ???.

[techbotics]

Been raining lots up here is water heavier than petrol?

Blocked drain tube?

Damian sorry just occurred

[Spanish S2]

Many thanks for your replies lad's, I'm thinking that expansion could be the reason. After filling up I went for a fifteen mile blast and came home. Temperature last night was 8 degrees, this afternoon 25 degrees. So hope that solves the mystery. Thanks again.

[glenrobbo]

25 degrees?
It feels like 25 degrees here in the NW of the UK at the moment.



Fahrenheit.

And it's wet & very windy.

Spanish S2, you lucky man.

[lewdon]

15 miles would use about 2 litres so would then require 40degC temp difference to make it overflow, so expansion doesn't explain it all, was car on the level? as slight tilt to the side might make the difference.
I thought that "panting" of flat sided tanks is more of a dynamic issue. (vertical movement on board a ship or cyclic pressure from a pump) so I am not clear how it would cause a volume change when the car is stationary. But I don't know enough to question Glenrobbo's theory.

[ijbd]

Yes,

and on top of that you have to allow for the thermal expansion of the tank itself when it heats up the same degrees C/F assumed for the contents.
This reduces the calculated overflow.

mvg Boudewijn

[techbotics]

Agree I am assuming fuel was colder in underground tank than ambient temp. Slope is likely as well ?

Never had this problem I think mine has only been full at the start of trip to s club.

Damian S3

[Top Gear TVR]

how about a slope? fill up with filler at high point, park with filler at ow point?

Or if it were me, more likely I went for the drive before I filled up and then forgot as it warmed up.