Just got 2004 audi a6 2.5 v6 tdi first thing on a morning when stone cold starts no problem but if I go for a drive and let it cool down it just turns over and eventually starts with a cloud of white smoke I put a full set of ngk plugs this didn't make a difference so I looked at the temp sensor unplugged it and it fired straight up o replaced this with a aftermarket seemed ok so was happy till it started again so I bought a original Audi one with new o ring and the problem is still there only when been ran and left to cool down but if its overnight left will fire straight up thanks in advance