[mrnickleye]

I've been there, done that. It boils over like that when the coolant level in the engine (not the bottle) is too low to keep the engine properly cooled.

When you shut the engine off, the coolant then touches very hot spots inside the engine and boils rapidly. This creates a sudden large amount of pressure, thus pushing coolant into the bottle.

Mine turned out to be a BHG. Very tiny (I found it when I looked the gasket over closely) hole at #6 cyl was allowing combustion gasses into the cooling system, and pressurizing it so much that I was losing coolant into, and out of, the bottle, while I drove.

The gauge read normal while I was driving. Then, as I slowed down for traffic, the gauge shot up a bit, then went back down as I was able to speed back up. This happens because the hotter coolant touched the sending unit and made the gauge jump up.

In the morning, fill your radiator up, and bottle 1/2 way. If it starts and seems to run ok, take it by a shop After school to have a 'block test' performed to see if you have a BHG.