We are all quite familiar with how annoying it is to bleed a VQ35 cooling system, but I'm having a really difficult time here. I can't figure out if there's a leak somewhere, or possibly a blockage. I bought a 2006 G35X a couple months ago, and the seller told me that it was diagnosed as some sort of blockage that needed further teardown. I assumed a head gasket leak, but I haven't gotten a positive result on a combustion gas leak test. Maybe it's a super small leak and that's why, but who knows.
When I pressure test the system, it loses pressure slowly. I cannot find ANY leaks ANYWHERE. I vacuum filled the system, then topped it off with the bleed screw open. Then used a bleeder funnel with the front end raised. By the time it's hot and the thermostat is open, you can see bubbles rushing in through the stem of the funnel. That's what happens while driving, it just pushes the coolant into the overflow until it eventually pours out of the cap. It actually melted some of the core support since it was gushing over so badly. I've followed all of the suggestions of revving it, letting it idle, heat on high, etc. and that has not helped. I still have bubbles rushing in.
Interestingly enough though, the car has never overheated on me. I haven't driven it more than 20 minutes at a time though.

I think to be sure, I'm going to do a leak down test, but I just wanted to post this to get some ideas as to anything else I should check first.

 

I did a leak down test and can confirm that there is NO air escaping into the cooling system. Is there anywhere else than can be leaking and not show? Maybe a strange water pump issue? It definitely seems to be working, given the way the coolant level rises and falls as it's revved.