>The tester is screwed on in place of the pressure cap and then pumped up
>to pressurize the system, with the engine stopped.  Then you start
>looking for leaks and watching the pressure guage.  For very slow leaks, you
>can leave it pumped up all day until enough coolant has leaked to be
>visible. 
>

This struck me as a really expensive but useful toy.  Why not take an old
inner tube and cut the valve stem out of it, leaving the brass pipe nice and
bare.  Disconnect the overflow tube at the overflow reservoir and insert the
valve stem and clamp it in.

  A bicycle pump would inflate the system I think, allowing you to put it up
to its overpressure setting, 16psi, before it blows back. 

 If you wanted to monitor the pressure drop, then you would have to disable
the pressure relief spring somehow. Maybe get a junkyard cap and make it
into the pressure tester.  Buy one of those snazzy electronic tire gauges
and check pressure 'til bored, then go check tire pressure too.  Let's see
you do that with that $120 gizmo.

Tim (Scrooge) Smith, bah...