On Sep 9, 2013, at 5:17 AM, Richard Golen <rgolen@HOTMAIL.COM> wrote:

the overflow tank gets completely filled. Sometimes, the coolant level is so high that coolant sprays from the vent hole on the top of the tank.

The tank slowly goes back to normal level if the van sits for a day or so, or if I let it idle for a while after the engine is cooled down.

While driving, the temp gauge is in its normal position. I've also bled the system a couple of times using a "bong".

Any ideas as to what could be causing this?

My nickle is that your blue pressure cap is going/gone south on the main pressure tank.

bob