Could cold fuel cause bad MPG?

[Ben]

I have only managed to get just over 400 miles out of the last couple of tanks. I usually get 500.
In the summer I put an inline filter in, to rule out air getting into the standard fuel filter housing.
Now I am wondering whether due to the drop in temperature over the last couple of weeks, the fuel is below an efficient temperature?

Could this be the cause of such bad MPG? I would have thought once the engine was warm the fuel would get heated when in the pump, but maybe the standard filter housing is still required?

Thanks for any input, Ben