Cadillac Repair: 1997 Cadillac DeVille DElegance, blown head gasket, replacing head gaskets

Question
1997 Cadillac D'Elegance model, 4.6 liter engine. It was running a little hot, so I took it in to a mechanic and he said it needed a water pump and a thermostat. Then he called and said it needed a radiator and a housing that was pitted. He fixed everything, said it was running fine to the tune of $1700. I the picked the car up drove it about 10 miles and watched the temperature rise above 250. The light came on and said turn off engine. I was on the freeway, so I coasted off to the side and turned it off. I cautiously opened the radiator cap from the side with a rag and it blew out a bunch of gunk, sawdust looking stuff and clumps of whta looked like calcium. I called the mechanic, he towed it to his shop, put in a new thermostat, flushed the engine and said it was still overheating and that the head gasket was now blown. The mechanic said he called the dealer and the dealer told him there was now way to replace the head gasket and that the car needed a new engine. This is a nightmare. The car wasn't bad the way it was, and now it's ruined. What I need to know is: 1) Does this repair scenario make sense?; 2) Is it possible to replace a head gasket, and if not, why not?; 3) How should I handle this with the mechanic? Many thanks...  

Answer
It would appear to me that the FIRST thing you would check for was a stuck thermostat and then test for a blown head gasket. Appears your mechanic isnot very good at diagnosing engine problems and you most likely did not need all thoses parts.

Why the dealer does not want to replace the head gaskets is most likely because he does not want to do the job and would rather sell you another brand new engine where he can make a bigger profit.

Shop around to some larger automotive repair facilities about replacing head gaskets.

tom