[Vwdiesel] Foamy expansion tank but no big pressure issues??

[Will Taygan]

I've got 1000 miles on this completely rebuilt 1.6NA in '82 Westy #2,
and I'm trying to figure out what's going on.  PO blew his engine
because the coolant leaked out from "somewhere."  I replaced all the
hoses, but not the steel lines, radiator and heater core.

Radiator stays topped off with coolant, it'll push out a little if I
open the bleeder valve right when I start the van.

The coolant reservoir gets a little bit low while driving even 20 miles
or so, and it's not pulling fresh coolant from the overflow tank.

I put a pressure tester on the system, and didn't see any pressure
buildup in 3 mins (well, when I revved it and it started heating up I
saw the pressure drop on revs and go up when let back to idle).

There are obvious bubbles/foam coming from the octopus hose to the
expansion tank.

I always assume this is a head gasket issue, but dang, it's not
overheating (drove it 75 miles today), and it's not having pressure
issues.

I don't see any obvious leaks when pressure testing the system, although
it does drop a teeny tiny bit (maybe 1 psi over 2 mins?)

I need the van to be reliable to travel remotely with small children
this summer, pulling the head isn't a huge job - more of an issue is
that my rebuilder's on vacation.  Furthermore, I'd rather get the rings
all broken in before I open this thing up again.

Any other possibilities/experiences that WEREN'T a blown head gasket??

Thanks,

Will in Alaska.