I have found the distance remaining varies on how I have been driving.
For example, yesterday it said 90 miles to empty as I got on the
freeway (I live about a mile from the freeway). After a few minutes
it was up to 110 miles to empty. So it seems to track your recent driving
habit to predict the number. I suspect this is the best way to go when you
have one or two gallons left and most people probably use this readout as
they get near an empty tank. When you have a full tank it is less precise
because the further into the future you try to predict the less accurate
your prediction will be (you could spend the next 5 days in city
driving or the next day on the highway -- the system has no way of
knowing this and the distance to empty would vary greatly between
the two conditions).

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