Cool fuel is denser than hot fuel, same with air, the molecules get closer together when cooled.
The main reason why everybody wants a cool air intake and a cool can for their carb.
The denser the fuel/air < the more bang you get.
On another note: hot fuel aeroates more, kinda like how a hot beer/coke foams up which in turn makes the pump less accurate.
I used to work at a brewer (coors) for 7 years, you had to keep the beer and the filler around 33 degrees in order to keep from getting short fills.
Cp