Didn't see any bubbles while it was running. The water just expanded when the temp went up. It has never gotten hot with me. Of course I just acquired the car a coulpe of weeks ago and I am still finding stuff that wasn't address before I got the car. Will let you know where the water level finally goes to.
Can you watch the water level rise and overflow the overflow tube at idle?
I strongly agree with Jim that 1 1/2 gallons lost means something serious is wrong. This is not just a matter of letting it seek its own level; that would probably be completely dry and then, in short order, a trashed motor. This car should not be driven until this is fixed.
If you see no bubbles while the water is rising, there must be a blockage. It could be in either the radiator or the motor. I once had a shop rag left inside the head after an engine rebuild.
You can do a crude check of radiator flow by disconnecting the hoses, plugging outlet and inlet with a rubber ball or something, filling radiator with water, then timing how long it takes to drain after removing the outlet ball. Most sources say no longer than 4 seconds. IMO, this is not highly reliable but it should indicate if there's a serious blockage. Maybe while you've got stuff disconnected, you could try back flushing the block; maybe you'll get lucky and knock something out.
Another, even easier radiator check is to run the palm of your hand across the front of the radiator while the motor is warmed up and running. Tubes that are blocked will not be as warm as tubes with hot coolant flowing thru them. ALso, properly flowing tubes will be cooler near the bottom of the radiator.
It's time to have a serious talk with the guy who sold you the car: what, in detail, was its recent history? Could the block be full of rust, or a mouse nest, or ....?
As my family physician used to say to me, "You are what we refer to as 'an interesting case'".
Steve