Sluurp! Gurglwgurglegurle...

[alloydog]

Or:
I thought fuel tanks/filler caps had air vents.

We've been having some pretty hot weather recently - about 32'C, which is hot for Finland. Last week, we drove up to see the Mrs's folks. It was about a 500km drive. The temp hit the low 30's and the humidity was very high. The air conn had to work seriously hard.
The fuel consumption for the northwards trip was pretty bad - we normally get the full journey in less than half a tank. But this time it drank nearly 2/3rds. When I opened filler cap, it made a load slurping noise followed by gurgling. I checked it later in the day and it made the same noise.

It acted like there was a vacuum in the tank. Does this sound right? I though there was supposed to be some sort of air vent in either the filler cap or the pipe between the filler and the tank.

Anyway, the temperature has cooled a bit - it is now mid-20's, and the noise no longer occurs.