When the engine is cold, the thermostat will be closed and no coolant
will be going to the radiator. A radiator blockage should therefore not
matter nor be the cause of this problem. I'm afraid that one of the
heads is not sealing where it meets the cylinder. Possibly a foreign
object came between the head and cylinder before it was torqued. Since
it happens as soon as the engine is started, it may be possible to find
it with a leakdown test.

Mark

Stuart wrote:
>
> Chris,
>
> Did they flow test the radiator?  Something is blocked if it builds
> pressure from the water pump trying to move coolant when the engine is
> cold.  Find it!
>
> Stuart