Coolant Pours Out of Rad Fill Neck

[SEMORiverHills]

1998 Venture, 3400, just completed head gasket job on 12/6 (head gasket was bad at cylinder # 1).
Last night, I went to test the protection level of my coolant with one of the ol' cheap 5-ball test tubes, to make sure that my coolant mix is potent enough, given that I did a fill/drain with water, fill/drain with Prestone Super Flush and water, then another fill/drain with water, before putting in the actual coolant mix. I was worried that an excessive amount of plain water may have remained in the system, and might dilute my coolant too much. I mixed the coolant 70/30 to be on the safe side of things, but I wanted to test it anyway just for peace of mind.
Well, when I went to remove the radiator cap (engine stone cold), coolant started to run out of the filler neck and onto the ground. I quickly capped it back off again, then removed the cap once again. Same result: coolant running out of the fill neck (best way I can describe the flow rate is like if you were pouring it from a pitcher).

In my estimation, this can't be normal. My reservoir bottle was filled to the 'Full When Cold' line, so no overfill situation there. Any ideas on what might be causing this, and how concerned I should be?

Also, one additional question: when I drive the van, the coolant never rises in the reservoir from the 'Full When Cold' mark. This concerns me a great deal, since on my 1995 Grand Prix 3100, there are two marks, 'Full When Cold' and 'Full When Hot,' and the level always rises from one to the other.

Thanks so much in advance for any insights!

[LMP]

With the recent multiple emptying and fill-ups you have made, some air might still be trapped in the system and leaves some void for the expansion of fluid, hence if does not have to flow out ....so I'd not be totally worried at this time.
Now just know that air IS soluble in water and it WILL eventually be carried out to the reservoir and released at each operation cycle and after a limited number of heating and cooling cycles, your cooling system should be totally air free. Releasing the purge valve on top of the thermostat housing will accelerate the process by removing some of the void so expansion can now force some of the coolant to and then from the tank.
Extensive "air extraction" procedures as often recommended are just needed if one wants the system air free right from the start, specifically to avoid what you experience now, which should be finished soon.
I wish it ends there after the efforts you have already made.

[SEMORiverHills]

Thanks for the input, I totally agree that any air trapped in the system should eventually migrate to the reservoir bottle and then out. I did bleed the system using the bleed screws on the thermostat housing and the other near the water pump per procedure, but I'm told that procedure itself often isn't enough, as there is a corner of one or both of these heads where air tends to collect and is very difficult to 'force out.' A reputable local dealer told me to just keep a close eye on the temp gauge, and that what air remains would eventually work out of the system, just as you have described. There is something to be said for the peace of mind that comes with a second opinion!
On another note, should I be concerned about the fact that the coolant level in my reservoir bottle never rises at all after a driving cycle? This is the first vehicle that I have encountered of which that level does not rise from some level when cold, to some higher level when hot. Any insight you could provide there would be most helpful.

Thanks again!

[LMP]

Originally Posted by SEMORiverHills

On another note, should I be concerned about the fact that the coolant level in my reservoir bottle never rises at all after a driving cycle? !

Yeah as said in my first reply, I think the air "void" is enough at this time to accept liquid expansion so it does not need to migrate to the reservoir.
I would simply drive the vehicle with the radiator cap loosened...so no compression of air could occur hence it will have to expand and push the excess to the reservoir. This will help purge the sustem.

[j cAT]

if you did not put the proper amount of coolant [antifreeze ] in system and ice formed in engine this will cause coolant to be pushed out as the ice expands. before flushing with water when not draining engine find capacity of your cooling system. then when draining system take note how much you can drain out. on 94 s10 6cyl. this system has 15 quarts capacity only 10quarts can be drained out this means i must put in 100% antifreeze because 5quarts of pure water is traped in engine and heater. this ends up being about 65% coolant 35% water for maximum protection. i hope this helps.........