Tips for filling up with petrol

The “Evaporative Emissions Control system” canister does two things: we’re both correct. When the engine is running it feeds the fumes back up to the throttle bodies (opens and closes a valve and lets the vacuum draw it back up to be burnt). When the engine is off, yes: it’s just a carbon filter.

Clever idea really…

I did read an article that said to try not to fill up on Fridays as that’s when the garages know people will fill up and the petrol price gets raised. However I’ve never noticed it come back down on Tuesday mornings!

Per tank is the only useful measure to a motorist.

Assume:
£1 = 1L = 1KG then 10KG of petrol filling 10L of space would cost you £10 at normal ‘cold’ density.
Also assume there is a 10% loss between normal and warm.

In heat, you would get a less dense petrol and thus less weight of petrol. So your £10 has got you 9KG of petrol filling 10L of space, not 10KG despite having pumped 10L. You are correct and you have indeed got less than you paid for.

My point is your normal petrol will become less dense due to engine heat, so expand and then escape inside your fixed volume tank. You now have the same 9KG of petrol as if you had filled up with warm. You have paid the same price. You observe the difference evaporating from the filler cap.

The difference of day temperature is only that the 1L is in the air and not resale-able by the petrol station.

I can see how the mentality ‘I paid for it so if I want to push it into the atmosphere it’s better than those gits selling it again’ but compared with changing your habits? Petrol density would only change at most by 2% in the most extreme UK climates anyway.

That’s the bit I disagree with; you’re essentially saying the following…

For a given temperature increase:
Money lost at the pump = (the monetary value of) petrol lost owing to evapouration

…and even if this were possible, you’d have to specify a timescale over which the evapouration can take place. If I lost even 30p’s worth of petrol to evapouration in the time it took me to go from one refuelling interval to the next I’d probably swap the bike for a horse and cart!