I'm losing about a gallon of coolant/water in about 30-40 miles of driving in about every couple of days. No more leaks from hoses and newer thermostat. I get a steady stream of coolant vapor from the overflow tank bleeder hose adjacent to the cap at operating tempurature (80-90C)

The most troubling test I ran is that I get a steady stream on large bubbles from of overflow reserved tank when 300TD is running with cap off. I needed to completely top off the reserve tank to get the bubbles. I guess it needs to be full to see bubble coming from hose coming from radiator.

Is this a definative sign that I have a cracked block, head or blown head gasket?

Are there any other test or symptoms to observe to confirm that the head needs to come off?