Drew
Sorry about your problem, it sounds bad.
your coolant is probably going out through your exhaust pipe through cracks
or a leaky head gasket
It's even worse in the case of a rear engined van if also the pressure is
pushing air into the cooling system you can get a thing called an air lock.

In this case the coolant won't circulate past the trapped bubble and you
will overheat probably ona hot day in heavy traffic. Other readers can give
you details for sure.
good luck

Gnarlodious

Drew Bedford wrote:

> I'm experiencing dissapearing coolant. Here's the scenario: I fill the
> cooling system, bleed everything I can and close it up. Then I drive
> about ten or fifteen miles, pretty heavy traffic and hills, and the
> blinking red light comes on. The coolant tank has dropped by two-thirds.
> I check the overflow tank, thinking the coolant cap is faulty, but
> nothing there. I've checked all the coolant pipes, head gaskets and
> connections for leaks. There are none visible. The only place I see
> water/coolant is a fine oily mist out the tailpipe. This has happened
> for a while, but is now getting worse. What's up?