you might be able to help me , is it normal that after the engine has been run for a while & cooled down that the top inch or so of the radiator to be empty of water ?
zetec 1.8 by the way

If you have it, (the car), set up with a header tank, then no, rad should be full at all times. If the header tank is set too low, this can occur. I had the same problem, and raising the header cured it. Regards Ray

This can also happen if you overfill your rad.
When hot, water expands and has nowhere to go so it is vented via the rad cap. Also air in the system can cause you to lose water.
A pressurised expansion bottle is a good way around this but make sure that it is higher than your engine and that the larger bottle inlet is spliced into your lower rad hose and the smaller pipe is attached somewhere in your top rad hose.
This will help to bleed any air out.
I have a K series engine with a head bleed, so I also attached this to the smaller bleed pipe.