it's starting to give me the s**t, what happens is the low water light comes on so i top up the level to about 1/2 way up the expansion tank, all is well for a while then i find the level slowly drops until once again the low level light comes on again, it doesn't seem to drop any further if i don't top it up, it seems to get to a level where the light comes on and stays there at that level

the light comes on when you 1st start up, after driving for a couple of k's the light goes off

i replaced the level switch and float about 6mths ago, so that's not part of what's happening

anyone else have this problem too?

Are you sure its not continuing to drop? Sounds like your topping it up when the light comes on.
Check for a leak around the reservoir and the hoses attached to it.
Do a pressure test if you cant find a leak.
Check oil for coolant contamination.

Have you looked for any tell tale sign of coolant leaking? Most coolants leave a stain

I am having the same problem and mine does relate to replacing the float, thats where its leaking from, I'll fix it one day.

have you checked the oil for a milky discharge? hehe, sounds porno-ish.

Don't alarm bells start ringing when you have to keep topping up the expansion tank?

Sounds like you might only have a leak when the system is pressurised, and when the cooling system pressure falls to a certain level, the leak stops.

It could be leaking into the head, a compression test might show that. If not that, check all the hoses for leaks. Specially the 2 o-rings (into thermostat housing and into back of water pump). The one in the water pump can go on leaking for ages and no one will find it, as it drops water straight to the ground. Doesnt hit the block and burn and leave marks.

Check on top of the alternator for whitish marks, or get a torch and look into the back where the hose meets the water pump and see if there is any green coolant sitting there waiting to drip out.

Seen this happen on 3 cars in a week, and no one could find the fault until they looked right into the hose joint.

A bloke at work had the same problem. It would drop to just below the sensor and then sit there (and would not drop anymore). In the end it was the easiest fix. He removed the wiring plug and presto, no more annoying light.

I had the same proplem in my AU
It turned out it was the radiator cap

Also check radiator top and bottom hoses.
Fairly easy to spot leaks there.
Probably easiest way to check if it's an exterior as opposed to internal leak is to park it on dry ground overnight and check for a puddle in the morning.