Not true, the cap can stay off at all time, it as nothing to do with
"Flow". But it works both ways; I did both over the weekend. I fill and
empty the van twice; bleeding with the cap close the second time and the
result was the same. But anyway, my bleeding was fine. The problem was a
faulty NEW OEM thermostat and a faulty NEW # 1 temp sensor. Luck was not on
my side this weekend...

Revving the engine is the key to a good bleeding, closing the cap when
engine is at 2500 RPM and shutting down the engine give a burst of
pressure, it help getting rid of the air pocket.

But that's irrelevant; I am going in prison for my sin...
Ben

87 GL, now call the beast
http://www3.sympatico.ca/huotx/engine1.htm