TOY: Temp help part 2

[Sean Flynn <sflynn@xxxxxxxxx>]

  Ok everyone, I've got a weird problem here that I hope someone can help
me with.  I have a newly recored rad, new thermostat, new water pump, new
rad cap and tons of coolant.  What happens is generally (but not always)
on startup the truck warms up like normal but the temp guage keeps
climbing.  I jump out and check the rad and it's cold - the tstat isn't
opening I suspect... which is why I've replaced the thermostat.  Still the
same symptoms.  Find that when I crack the rad cap, instantly the temp
drops to normal and stays there (and can feel heat entering the rad)... so
replaced the rad cap.  Still the same symptoms.  Sometimes if I play with
the heat level control it'll sort the issue out (sliding it to cold is
sometimes the cure, sometimes sliding it to hot) and the coolant will
start to flow to the rad.  Since this happened on 3 different thermostats
now, I can't believe I'm _THAT_ unlucky.  
  So what do you think?  Air trapped in the system is my only guess... but
how can I get it out if that is the problem?

	Sean