Originally posted by csnow
Perhaps the expansion tank is over-filled? Otherwise it should never come out the top.
I suppose there could be a leak in one of the hoses, or the tank itself.
...or the coolant tank cap isn't screwed on completely?
There are two sets of detents on the tank lip. If the cap isn't securely tightened past both sets of detents, you have insufficient tank pressure and it will manifest itself by trickling out when shutting off the engine.
Are your hoses collapsed when you shut down?