Hello, can anyone help me or give me some advice please.

About 3 weeks ago whilst taking the kids to school i noticed a ploom of white exhaust fumes coming from my 406 hdi, i got home and sure enough mayo in oil filler cap, head gasket! The next day i cleaned the oil filler cap out, topped the coolant up with water and it started fine, no white exhaust smoke. I drove it to the garage who said it didn't seem like the head gasket had gone. They told me to change they thermostat, which i did.

now i have been driving it for 3 weeks; no loss of power; no white smoke; no mayo; the heater/climate control work fine; temperature guage is normal, 90 degrees when fully warm.

The problem is I'm having to top up about a litre of water every day. Also i bleed the cooling system every time too, some days it has a lot of air other days a little.