...yea that was a typo, my last sentance should have read:

doesn't the rad cap seal SEALING DOWN TIGHT when cold?
I tend to open the spider tank and stick my finger in on a normal day,
and I feel water about 1" down from the top top edge, and never saw
any transfer to or from the overflow bottle.

...but after taping over my rad and achieving 200deg temps on my
CHT probe (thus actually getting some cabin heat now!) I was pushing
water out of the vent hole in the overflow bottle. When I then checked
my spider tank when cold, none of the fluid pulled back in.... thus
leaving only 1/2" in the spider tank and a full overhaul bottle.

Thoughts? methods to test? I suppose I should pull the overflow line
off the spider tank and suck with my mouth to make sure fluid will pull back in. Does that overflow tube need to be FULL of coolant? Or
can air pockets exist in the tube going to the overflow bottle? Seems like even with air it SHOULD suck back in when it cools....

Lastly, it's 50/50 Dex.

Thanks guys! ~Wild