The waterpump is always pressurizing the radiator. The thermostat is on
the return line from the radiator. Coolant won't flow through the
radiator unless it has somewhere to go. The open bleed screw gives it
somewhere to go even when the thermostat is closed.

Mark

David Brodbeck wrote:
>
> Dennis Haynes wrote:
> > The cooling system should not be opened or bleed with a warm engine.
>
> Hmm...but how can you bleed the radiator properly unless the thermostat
> is open?  I get basically no flow until it starts to open, and that
> doesn't happen until about 190 degrees F.
>
> --
>
> David Brodbeck, N8SRE
> '82 Diesel Westfalia
> '94 Honda Civic Si -- For Sale