Went on a 30ish mile run on Saturday to take my daughter home and when I started the Saff outside her mums house she idled real rough and the street disappeared into a whitish fog cloud. Had to get home so I carefully pulled away with what felt like a misfire and still tons of smoke, got past about 2000rpm and engine smoothed out, no more smoke. then everytime I got stuck in traffic she obliterated everything behind her, but on the move no prob could rev through it. Kept at 60mph on motorway and she didnt miss a beat or overheat. When I got home I left her running and after about 10 secs she started running lumpy again and tons of smoke. I then left her alone overnight and checked coolant yesterday morning and it had dropped from just under MAX on Friday to under MIN. Everything points at HG. She s a DOHC with 134k on the clock and had a head rebuild and skim at 77k. Heard from someone on Sierra Owners Club site who had similar symptoms and found that his cyl. head was cracked Any ideas on sourcing a head if need be cos won t know if its f***ed until its off and Ill need to get one quick cos I live in the sticks where buses are nearly extinct! HELP!