expansion tank cap question

[hixsy]

right, ive done a reflush new pipes all that stuff, ive bought a new cap for the expansion just to be on the safe side.

with the old cap i could take it off and blow through it both ways, not freely but it would go through. when the engine was running i could see the coolant going backward and forward from the expainsion to the filler, since ive put the new one on its not doing it anymore. to blow through the new one in both directions is very hard, is this right? was it ok with the old one or is the new one working? my engine runs hotter with the new one on it and i cant see any fluid flowing between the expainsion filler when the new cap is on, ive ran it up to temp the rads hot and the thermostat pipe is too, i thought when the system got to pressure it would let the coolant back into the filler tank, but i can see no movement when i rev it between the 2 tanks. im confused yet again....

ive followed the coolant bleeding procedure i found on the brickyard forum, and it seemed better with the old cap, but surely a new cap should be right ?

thanks in advance