[urq] boiling coolant after shutdown

[Ed Kellock]

It's very cool here this morning for a change so I decided to drive
the urq to work.  I had the heater valve wide open and the engine
temperature never exceeded normal, the cooling fan did not come on,
even with a minute of idling after reaching work.

Inside the hose from the neck on the front of the head that goes to
the top of the radiator, the coolant was very obviously boiling.  Is
this even remotely normal?

History: On June 25th, at 3am, I was on my way to meeting everyone to
go up the road to the Pikes Peak Hillclimb.  I had been driving the
car regularly prior to that and it was running great.  It was cool,
jacket weather still in fact, and I drove very sedately for about 5
miles, stopping off at a 7/11 for some coffee.  When I restarted the
car to leave, the coolant low level warning was on.  A leak had sprung
under the clamp on the lower rad hose at the thermostat housing.  I
refilled and drove a few more miles to the meeting place.  I stopped
and refilled and then drove a short bit more where I finally ditched
the car at the gate of Pikes Peak and rode up with Bruce Bell.  Later
that day, I retrieved the car and drove very carefully and
uneventfully home where a couple days later, I replaced the offending
hose with a spare from Ben Howell (Thanks Ben!) along with a new lower
temp thermostat and a new thermo-time switch at the back of the head. 
The next day I drove to work and another leak sprang, in the hose that
goes from the bottom of the coolant recovery tank to the bottom of the
radiator. I replaced that.  The next day the throttle cable came loose
from the pedal in a store parking lot during a hail storm, which being
the third strike in less than a week signalled the beginning of the
cooling off period between the urq and I.  Since then I have only
driven the car home from that store, one quick trip around the
neighborhood a week or so ago and then to work today.

The boiling in the hose was present back on June 25th, but I figured
it was merely a product of my low/leaking coolant tribulations then. 
Now, the system is leak free, with a new thermostat, which obviously
opens earlier and causes the car to run cooler, and the temp on my way
to work this morning was sub-70 and my drive was not spirited, except
for one light blast short-shifting into 2nd, then 3rd, to keep the
boost from falling off.  That wasn't more than a couple hundred yards,
followed by at least a half mile of 4th and 5th at 40 mph or so.

If you've read this far, thank you, and I appreciate any thoughtful
input you may have.  I'm thinking head gasket, but I tend to be
overreactive and paranoid sometimes, so I'm hoping that's the case
again this time.

Ed