grand voyager water probs
 

hi im a newbie wih my first voyager its a 3.3 grand voyager on an x plate [2000] model and i love it but its losin water out ov the overflow on the expansion tank and i have to put bout a litre ov water in the rad every three or four days and also no heat in cabin???? checked the head all is ok, been told it cud be thermostat but cant find it and noticed that the housin aint got a gasket on so losin a little water from there but when took the thermo housin off i couldnt find a thermostat inside??? does this mean its been took out??? please help someone its drivin me mad not knowing also i checked heater matrix and thats all ok too HAS ANYONE GOT ANY IDEAS PLEASE