Cadillac Repair: 1994 cadilac sls overheating, 1994 cadillac sls, blown head gaskets

Question
Hi. I just got a 1994 Cadillac sls v8 4.6 140000 miles.. The car is over heating: I check the termostat it fine rad has been flush. The water pump belt is fine. When I start car it can run forever at 190 deg. Then when I drive it for about 10 to 15 mins at about 40mph it go  up to 210 deg and then back down to 190deg.. but when I get up on it over 50mph and higher the temp shoot up real fast untill it reaches 255 plus engine coolant MSG comes on. When I pull over my fans are both working but I notice my top rad hose is hard and hot. Like it fill with air lock. I know Cadillac have a bad history of blow head gasket.. I know I could take out the spark plugs and run air to see if bubbles come out the rad cap I don't have the tools to do that though.. So if I take it to a shop what do I need to ask them to do to see if it the head gasket? And also does any of that gasket repair stuff that you can buy at auto stores work at all? Or is it a waste of money..

Answer
This sounds EXACTLY like blown head gaskets due to stripped head bolt threads in the engine block and is very very common.

PLEASE do NOT put any type of sealant in the cooling system as you will NOT solve your problem, You will be adding to it.

Have them do an air pressure test via the spark plug holes and watch for bubbles with the radiator cap off.