It does it @ operating temp, never when it starts, you are just driving along, suddenly you look on the rear view mirror and there it is, a thick cloud of white smoke..... takes 20 seconds and it's gone. You drive another 250 miles and nothing. I ruled out valve seals, since it always has clean starts, piston rings woud smoke almost all the time..... I'm thinking it could be a fuel inyection problem?? I have a brand new ECU, wiring harness, trigger points, pressure valves....they only thing I didn't get new were the inyectors. For some odd reasonn the air temp sensor (also brand new) messed up the engine so I disconected it. Could a bad inyector be casusing this?