Typically with cars made in the last ten years, if you don't tighten the gas cap enough, the check engine light will come on (mine does) so the car should give fair warning.

As for filling up at the coolest time of the day, I've heard gas doesn't expand/contract enough to make a difference in our car engines.

Ummm, if you get 30 miles/gallon, then 147 million gallons would power your car for 4.41 billion miles.

Also, I don't buy the 'pump when it's cool' thing as the gas is stored (and pumped from) underground, and the air temp will have virtually no effect on the gas temp. It won't warm up enough to matter until after it has already been pumped.

Right, thanks for fixing my calculation. 4.41 billion miles is larger than the distance from the sun to Pluto.

I suppose we'll need some sort of "independent verification" claim on the gas volume tip. If there's any sort of difference, it's must be very small. Found something. Here are the numbers.

The problems seem to stem from the storage temperature, which I would assume from the article is controllable. Storage temperature would be independent of the environment theoretically, so instead of worrying about the weather, it sounds like (if this article is correct) you want to find a station that stores gasoline at the same temperature it receives it or pays for it.

I actually encountered the "coolest time of the day" thing last week. Even though I normally fill up before 0900 EDT, I didn't get a chance to do this last week (or maybe the prior week). Whenever it was, it was during the recent heat wave in DC.

Anyway, I filled up and topped off (as I always do, don't bother arguing the point with me). I turned the nozzle upside down to drain the last amounts of gasoline into the tank. (This was recommended by the WSJ a few months ago. Instead of letting the fuel leak out when putting the nozzle back, you get most of it into the tank. This is extra gasoline that was pumped, which you are paying for, but typically doesn't make it into the tank. Small but I notice the difference in terms of leakage.)

Anyway, once I started the engine again, I noticed that the indicator was slightly off the full mark. Usually, it is slightly beyong the full mark (intentionally). This was sometime around the hottest point of the day, after 1400 EDT. Now, the difference is not monumental but it was very visible. I can't and likely won't measure it but I know what I experienced. The time of day does make a difference.

I have to make a comment about topping off. And no, its not going to be some environmental point about how you mess up the environment.

The fact is that topping off is bad personal finance, because the fuel pump's vapor recovery system just sucks the gas back into the system--it doesnt go into your tank.

So you're paying for gas you dont get.

The fill up at the coolest time of the day thing refers to your own tank of gas, the one IN your car. The gas in your tank heats and expands as vapor is formed through out the day. The heat is not only from the ambient temperature but also from the fact that your car heats up as you drive.
If you fill up at a "hot point" in your day, or after you have driven for a while, gas vapors will leave your tank when you take the gas cap off. Some leakage can not be prevented, which is why you don't smoke at the pump. However if you fill you tank first thing in the morning, before your car and the ambient temperature warms up, there will be a very small amount of savings.
The reason Khyron's tank didn't fill "overly" full as he/she likes it, is there was most likely a pocket of gas vapor inside of his/her tank preventing it from filling. While that pocket of vapor was small, it was large enough for Khyron to notice.
I apologize for using he/she, I do not know gender. Sorry.

I question the driving 55 thing, too. I have a 1998 Jeep Cherokee. It's bit of a hog, but I bought it in late 1997 and I remember filling up once in the summer of 1998 in Dallas, TX for $0.78 per gallon!

Anyway, I get my best mileage if I drive at 44 MPH or at 68 MPH. It is significantly better at either of these two speeds than any other speed, including 55.

It may seem counter-intuitive to some, especially those that know little about cars. But in my case, my engine has to rev higher in a lower gear to maintain 55. A higher revving engine burns more gas. When I get to 68, it moves up to the next gear and the engine revs decrease. So I get to go faster and burn less gas.

I have the built in computer, so I can see mileage in real time and on average. So I think that the best speed for any car in terms of mileage must be unique to each car, although many may in fact be around 55 MPH. I don't know.

I have a simple one - turn off your fog lights if you don't need them! Some people turn on every light their vehicle has, to help them be seen, even in broad daylight on a clear day. I will say that Daytime Running Lights (DRLs) make your car safer, and turning on the headlamps with the tail lights might be even better, but to also add in the fog lights is just a waste of energy. They don't add anything to safety as far as other drivers seeing your vehicle, as their light is aimed at the ground. Try standing in front of your car with the lights on and the fog lights on - the fogs just don't stand out anywhere near as much. even DLRs, which are low wattage, are amimed high - not at the ground, they do more than fog lamps at as littel as 5 watts each.

This mostly applies to factory Fog Lamps - if you are using aftermarket ones wired on thier own switch for your DRLs, instead of using the headlamps - that is fine. But, most factory setups won't turn on the fog lights until the low beams are already on.

Further, at night, most driving experts will say not to turn on your fog lamps unless there is poor weather or some other situation where they actually help - on a clear night, they just light up the area right in front of the car, and cause the driver to look there - instead of looking further down the road where the headlamps are illuminating. This causes reduced reaction times to conditions, as too much attention gets focused to close to the vehicle, instead of down the road at the far end of the normal headlamp beam..

Again - if you need them, use them - if not turn them off- that is all I am trying to say.

For those that feel that using lights on a car are for free, think again. Every electrical load increases the work that the alternator must do to create that electricity - nothing is free! Most fog lamps are in the neighborhood of 35 watts each- so at 60+ watts is a small load, but over the course of a year, it could easily result in a few gallons of wasted fuel. Even for $10 - I'd rather it be in my pocket rather than the Oil Companies or OPEC...

Walt