Mercedes Benz repair: mercedes sprinter 312d turbo, blown head gasket, exhaust gasses

Question
my van has been overheating i have changed the thermostat but it still tends to overheat although not as bad also i seem to be loosing water but cant see any leaks heater still blows hot and the sender unit is ok any ideas would be much appreciated thanks
year of van is 1996

Answer
Where are you loosing water? Is it coming from the overflow tank? If you are losing water through the overflow then your system could be pressurizing from a blown head gasket or a pinhole in the cylinder head that is releasing exhaust gasses in your cooling system and pressurizing the sytem forcing coolant out through the overflow.