Im fairly certain my head gasget has gone. In short; i am losing small amounts of coolant, the coolant system has been presure tested. I have got white creamy substance under the oil filler cap and a small amount on the dipstick. Occasionally i get lumpy idle when engine is cold, which i am told could be water being burnt off. If this is the case i will be getting a mechanic who i use for regular servicing etc to do the work. How many hours labour would a hg replacement take? I will be supplying the bits. What exactly will be needed?