I tend to wait until the gauge is about 20% full before nipping to the petrol station and then usually filling it up. I've been told different things by different people. Some say you fill it till half as there's less weight, but then I wonder about all the unnecessary things people carry in the car that would more than compensate for say the weight of say 20 litres. I've been told that I should fill to max when it's down to half and then do it fairly early in the morning as the heat affects it. I tend to fill it to the max as money isn't that tight and can't be bothered with additional trips to the filling station.

Is there any kosher mechanical advice about the optimum approach to putting petrol in the car?

I wait till the light on the dash appears then fill it to the brim, as for filling when cooler, meh, my car always seems to take onboard the same amount no matter what time of the day or night i fill it.

Ms. bino makes the same silly argument about filling the car in the morning when it is cooler, but I don't think it makes a huge difference- maybe a few milliliters, but certainly nowhere near a full liter.

Our VIOS has a stupid digital gas gauge- broken into 8 segments. I like to fill the car on the third to last segment-IE before a quarter of a tank, so that we don't get caught short in a traffic jam. Nothing worse than being gridlocked with a blinking fuel light on the dashboard!

undergound tanks in LOS are not very affected by heat, its around 25-28 degrees 24 hours a day

tanks not undergorund, in the morning you get approx 5% more fuel (in kg) than late afternoon. dont remember the exact numbers, but 50 liter is approx 42 kg in the morning (25C) and 38 kg in afternoon (45C)

Think the worse thing is letting it get really low and the sediment in your tank bottom gets moved about in the slosh and finds it's way into the lines, eventually filtered l know but not good practice.

letting it get really low frequently can damage fuel pump. Pump is cooled by fuel, and overheats when very little fuel left

Think the worse thing is letting it get really low and the sediment in your tank bottom gets moved about in the slosh and finds it's way into the lines, eventually filtered l know but not good practice.

letting it get really low frequently can damage fuel pump. Pump is cooled by fuel, and overheats when very little fuel left

Indeed, l remember the old Triumph TR6 had the pump in the boot and had big probs with heat and the 'cure' was to wrap soft copper tube around it connected to the fuel line so the heat was taken away by the constant flow of new fuel. but good to talk (l hope ).

since mid 80s most cars have pump submerged in tank, and the less fuel the warmer pump. in curves it also sucks air making it very hot

It probably pays to keep your tank as full as possible at all times to prevent an accumulation of water which is deposited in the tank from the condensation occuring in the air in the tank. This is the strategy aircraft users use.

When I need petrol I fill up. And that's that!

1. Fuel light comes on

2. Fill up (full) at my local PTT

3. Repeat from 1.

When I need petrol I fill up. And that's that!

Agree! Except i like to fill up for longer trips.. Nothings like cruising from CM to BKK with no stops

When the light kicks up you have about 30 to 50 km left on fuel ( depending on model ).

When the light kicks up you have about 30 to 50 km left on fuel ( depending on model ).

or 80 to 120 km, depending on model

Yes, I have 120 kilometers left when the light comes on. Very handy.

When I need petrol I fill up. And that's that!

Agree! Except i like to fill up for longer trips.. Nothings like cruising from CM to BKK with no stops

yeah me too, except when the wife is with me, 1 stop an hour then, at least!

When the light kicks up you have about 30 to 50 km left on fuel ( depending on model ).

or 80 to 120 km, depending on model

Offcourse...

There is also the school of thought that says an empty tank allows for more vapour headspace, and therefore more evaporation of fuel. This would be particularly true for gasohol, since methanol has a higher vapour pressure than pure petrol.

Also agree with the statement above regarding emptier tanks allowing for more possibility of water condensation inside the tank, especially in our humid climate.

Given all that, I usually top off when my gauge indicates about half full.