bubbles in radiator

Not sure but if the radiator is staying cold it sounds like the thermosta isn't opening. Take it out and put it in a bowl of hot water an see if it opens. If it does you could be fitting it the wrong way or have a blocked radiator hose. Try running the car minus the thermostat the rad should start to get warm.
I stand to be corrected on this as I'm a pretty poor mechanic.

I think Navarman is spot on with the thermostat. If it's hot and the radiator is cold then the coolant isn't getting past it. Test it as suggested but if in doubt put in a new one.
Blowing bubbles back through the radiator seems to be a separate problem. It usually means a crack in the head or a faulty head gasket. Basically you are getting the bubbles from the gas leaking from one of the cylinders via a crack in the head or a faulty head gasket. I think the repair of the gasket might be a problem as there's a lot of pressure in the cylinders and the gasket needs to be perfect. Another test for this is to release all pressure from the radiator cap, replace the cap, wait a short time (30 seconds) and release the cap again - listen for escaping gas indicating a build up of pressure. Pressure is meant to buid up with heat but not as quickly as it does if there is a leak from a cylinder.
Good luck!

Gday ,

never reuse a head gasket, more then often you find yourself pulling the head of again, not to often they will work second time around, the only suggestion I can give you is to put a new head gasket on, on pray that the problem was re using the head gasket, as you had the head tested for cracks and I hope the valves checked and checked for any warp while you had it off, then chances are it is the head gasket.

Clive

Just a thought
Some engines require a special thermostat. Have you checked that
Ray

Just thinking outside the square here. Is it possible that you have put in the thermostat upside down on this engine?
Regards Andrew.

Hi there
This does sound like head gasket is blown and you will have to replace it for it will blow good and proper sooner or later,as for your thermostat you could try running a non standard that has a cooler opening temp or running it without one at all.I have run plenty of motors without them and the older the motor the better they run.My wife has a holden berina 1995 model i took the themostat out over 90000 kms ago because of overheating problems that no workshops could solve so instaed of just keeping on forking out money to fix i took out thermostat against advise and it has now done 274000kms.I have done it with toyota 4.2 diseil and other motors good luck