Originally Posted by MikeS '06 330i
I always fill up when the tank is 1/4 full. Since your pump being submerged helps cool it, thus longer pump life, I never run the tank down to E.
^this. If you run your tank down close to empty frequently you will probably shorten your pump life.
I also usually fill up at half empty for a couple other reasons;
- It reduces the chance of condensation forming on the walls of the tank, which can be a bigger problem in the winter months. This is more important as I specifically avoid using any ethanol blends or gas line antifreeze, which is also alcohol based.
- Also, I have an x-drive, which puts a bit more weight over the front wheels. Keeping the tank full helps keep the car closer to a 50-50 weight distribution, and also provides a bit more traction to the back wheels on slippery surfaces (at the expense of more overall weight, of course).