just checked header tank and found to be empty, checked a week ago and was o.k no visible leaks ,just drove it 5 miles let cool and checked again all o.k , engine running o.k and at normal temp any sugestions could it be that the cap wasn't sealed properly has anyone else had this happen

What MY have you got?
I know that the rubber seals can harden and that lets out the water, its probably just something as simple as that.

Tony:D

it's a 94 , your theory sounds good

Check the coolant pipe to the turbo. The plastic connection to the resovoir goes like paper pulp and the hose eventually breaks off.