I bought, an a4 s line 1.9tdi 2006 model, four months ago. It has 87000 miles on it with a full service history. On christmas eve, I noticed steam, coming out of the exhaust. The coolant level has dropped to the minimum level. The car never over heated and no loss of power and there seems to be no white stuff in the oil. An ideas what could be the problem? Really bad timing, all the local garages are shut! And it is one month out of its warranty.