Tried to bleed the air out of the coolant system per Bentley.  Bubbles of
air/coolant eventually come out of the bleeder valve but then....    nothing.
Book says coolant should come out w/o bubbles.  Tried this 4 times and it is
always the same.  On driving the gauge goes up to mid-way and the fan comes on
regularly but no overheating.  Previously the gauge hardly ever went near half
way.  Help