Cadillac: Coolant loss/ head gasket, blown head gasket, coolant loss

Question
I have a '98 Deville w/northstar 4.6. It has 187266 miles on the engine. I've been experiencing problems w/ coolant loss.  We have replaced the water pump, thermostat, drivebelt and tensioner within the last days. With the intake manifold cover off, we were able to see some water/air bubbles at the rear head. Are we correct in assuming that it is a blown head gasket?  With the radiator cap off, after changing the thermostat, etc., the coolant did not bubble up until a lot of pressure was put on the engine as it idled. Once we backed off, the coolant went back down to normal.  How time consuming is it to do head gaskets, and can someone who builds hot rods, and works on 18 wheeler diesel engines do cadillac head gaskets?  How long can the car be driven with this problem, before it's completely out?  By the way, the car did overheat twice before we changed the thermostat, and water pump. Just for my own information; have you ever seen or heard of a northstar engine's starter housing busting while still installed?  A response is greatly appreciated.

Answer
it is your typical blown head gasket.

Yes, I have seen a few starter housing busted.

If you have EVER changed the engine coolant did you remember to put in the sealant pellets in with the anti-freeze to help seal the head gaskets as the manufacturer recommends ?.


Getting the back head OFF is a nightmare. With that mileage I would recommend pulling the engine and replacing all the gaskets and seals while I had it out of the car.