Useing water,
 

car 96 uk , new header tank (stainless) 1000 miles ago, checked water last week it was low >> nearly empty, filled it up, been out today 20 miles isshhh, low again, checked all the pipes all seem dry >> to me , any ideas, thanks Alan.

try and get it pressure tested at a garage. shouldnt cost much just to check.

Could be a weep from the radiator side /end caps. They are known to split and weep rather than pour out the contents.
good luck,

911

any more ????

Any steam from the exhaust?

Dont know anything about scooby engines, but the water is either being lost in the cooling system itself (you say its all dry) or in the engine.

Alan, if you cant see any obvious leaks then usually its the headgasket that has gone. I ran a Vito van for 6 months continually topping it up until it died. Long term, its best to sort it early as it works out more expensive when it completely dies :D