Er.... those figures seem more or less correct to me.... I get around 430-450 miles per tank from my 99 S70 T5 if I drive it gently (don't ask what it is if I put my foot down!).

One thing that may be happening is that the computer calculates fuel remaining according to the last 20 minutes driving. So if you've been stuck in traffic the figure should drop and then rise again when you get clear. If you were in heavy traffic before you filled up then you will get a low reading (same if you were caning it too ;-) ). As for the temperature, the colour of your car can have a bearing on this. A dark car when sat will accumulate a lot more heat than a light coloured one. This in turn heats the air around it and you end up with a high temperature. As you start to drive, the car cools a bit due to airflow and the reading returns to normal. Same happens in heavy traffic too...

Alastair