The tips are pretty much worthless, let me put on my Julie math hat
the tanks are underground, so the temp variance will be minimal even on a hot day. You can feel this by when you pump the gas the handle will become cooler. In addition this variance is pretty small in quantities under 20 gallons. For a couple thousand gallons it would add up, but in our cars the amount against the loss of convenience would not really make it a factor.
These are the numbers that I found as defined by US gov.
231 Cubic inches at 60 degrees = 1 gallon gas
234 cubic inches at 80 degrees = 1 gallon gas
I would doubt that gas would change outside that variance in underground tanks, but here is the math at 3 dollars a gallon.
(3/231)*100 = Percentage of difference about 1.3%
20 gallons of gas at 3 dollars = $60
601.013 = 60.78 or a potential savings of 78 cents. So assuming you fill up 2 times a week you would save at most .7852*2 or $54.78 a year. Wow that is 31,000 miles a year at 15mpg… so lets half that and call it $26 bucks a year assuming the gas is measured at 231 ci/g and is pumped at 80Degrees F every day. which I doubt would happen all year round. So realistic savings would be more like 10 bucks a year at most.
Hmm a little larger then I thought but the math works out, yes it is a difference but even in the extreme I do not see it as more then a $10 savings a year if you drive 15k miles a year.