When is the best time to go to get petrol/gas for your vehicle?
Does it make a difference with the time of day, if it’s raining, if a tanker has just been or if the garage is full or empty?
I heard it’s better at night when it’s cooler.
When you say “cooler” are you referencing the fuel’s volume/temp relationship? If so, many central fuel tanks are located underground and perhaps the outdoor temperature has little effect on the temperature of the fuel in those tanks.
The only time that I can say for sure is bad is if you are in Alaska in the winter don’t fill up on the way home from work at a station very close to where you live.
I had a tech from Alaska in class and he was complaining about cars being towed in where the vapor recovery system in the car was full of liquid gas. He asked if this was a general problem with our cars. No it isn’t.
I thought about it for a while and asked if these people parked in a heated garage? Yes they do. Are they filling up just before they get home? Probably came the answer. Well if the fuel is way colder than the air in the garage, then the fuel will expand when heated, and if the tank is full enough flood the vapor system. Have them fill up before they drive home, or not top off the tank.
I got a phone call back telling me that this had solved the problem. 
With underground tanks the temp does not vary much from day to night. Working in a gas station I can tell you that on hot days the nozzle is nice and cool. On cold night it is toasty warm. The air changed temp, not the fuel.
Fuel pumps here (Calgary, Alberta) and in Ontario say ‘Volume corrected to 15 degrees Celsius’.
This means that no matter how warm or cold it is, you’re still paying for the same amount of hydrocarbon molecules.
It’s better for air quality to not fill up in the morning or early afternoon on hot days, if that’s what you’re asking about (gas vapors+ sunlight = smog; if you fill up in the evening, even before sundown, there’s not enough sun and time to make smog before night).
When we get Ozone Alert Days, we are asked to fill up only after 6:00 pm. We are not a state that requires vapor recovery nozzles on the pumps, so pumping gas pushes out hydrocarbon vapor from the car’s tank.
Maybe that little piece of information contains something useful.
Rick, I know you love working on cars, and are always a great help here on the board, but I worry you might be getting a little to touchy-feely with that gas nozzle. 
I know this doesn’t exactly apply to what your asking , but l believe it’s worth sharing. You should keep at least a quarter tank of fuel in your vehicle. The ability of the fuel to provide cooling to the pump , however limited ,does make a difference in how long your pump will last. Living in Las Vegas and having sold hundreds of in tank pumps I assure it does. I know this won’t help a lot of you but anywhere it gets blazing hot it holds true.
That’s because typically cooler temps will “oversupply” the stated quantity -liter or gallon-(a disadvantage to the seller) if not corrected so, sure nuff, its corrected in Canada.
Here in the USA where most gas is sold during the hotter summer months a hot uncompensted pump will “undersupply” (an extra profit for the seller). So amazingly compensation is all over Canada but almost nonexistant in the states.
Just fill up when it is most convenient for you.
The 50 cents or whatever you might save by filling up when it is cooler is not worth the hassle, in my experience.
[Gollum]He wants the precious. Always he is looking for it. And the precious is wanting to go back to him… But we mustn’t let him have it. [/G]
I’d say the best time to fill up is some time from Monday morning to Thursday afternoon. That’s when they always jack up the price for the weekend.
Yeah i thought the cooler = more was either overly optimistic or out of date. Good to know that running your fuel really low can damage the pump.
Another consequence i’ve heard of running the fuel too low is dirt being too concentrated and messing with your filter. This is probably another urban legend from way back.
Ooh, i’ve just thought, if your tank is nearly empty and you fill up, the quality of the new fuel will be almost 100% uniform. There was a serious issue in the UK a few months ago with tainted fuel wrecking exhaust sensors on hundreds of cars. The ones that weren’t affected where those that were just topping up on a 1/2 full tank.
I suppose the economy aspect of running a ‘lighter’ vehicle is seriously outdone by the potential damage costs.
Good advice. But more like .5 cent.
It is deminimus.
As long as there is liquid fuel in the pump it has cooling. If it a two pump system and the intank prepump fails, then the main pump can fail shortly there after. Running the tank low with a failed prepump might shorten the time before failure, but it is the failed pre pump that is the problem, not the tank level.
You worked for Volvo as I remember it. The big three are too cheap for anything like 2 fuel pumps and they are the only vehicles I have experience with. Two pumps would be a redundancy. It’s funny though, although what you are saying is absolutely true it makes me think of an aircraft. But that’s Saab.