Cant get air out of coolant!

[Ijusfarded]

Having this problem with both my 98 dc2 and 98 ek (y8)... Followed the service manuals for burping coolant, and even after an hour of burping (squeezing hoses, revving up, heater core open, etc...) I still cannot manage to get the air out (still bubbling). Cant find any leaks

Did a chemical block test on both cars, both passed... so there's no way the air can be a blown head gasket..

What are some possible reasons I cant get all the damn air out of both cars?

Edit: I have repeated this process for several days on the dc2 and driven over a hundred miles