Bleeder valve opening on its own

[Hatzenbach]

Hi,

I am trying to troubleshoot high coolant temperatures (210 ~ 220) and
* replaced thermostat with lo-temp LN thermostat
* replaced water pump

So now I had to bleed the system. For convenience I left the plastic cover (the one which hides the bleeder valve) off for the moment.
This afternoon when I came back from lunch my water temp was 215 F, all fans were running at full speed and when I opened the rtrunk I noticed that the bleeder valve had opened on its own (it basically popped out as if I had manually bled it) - is this normal?

[very~worn~944]

This is normal. When the system builds pressure it opens the valve....have you checked your antifreeze level? The wrong ratios can cause high temperatures as well.