Headgasket leaks also cause things like the coolant recovery bottle overflowing even long before the engine is fully heated. This occurs as the added pressurized gasses leak into the water jacket from the compression and power strokes (in 4 stroke language)and overcome the psi setting on your radiator cap.
Then when you shut down the engine, the pressurized cooling system forces coolant into your now dormant combustion chamber. If the car sits for a while, this coolant will slowly leak past your piston rings into your crankcase. If you start up your engine shortly thereafter, the coolant will be blown out your exhaust.
You can check for a leaking headgasket by taking your van to a good radiator shop. They have a device that they can place over your open radiator cap while the van is running to chemically "sniff" for hydrocarbons in your coolant.
Alternatively, you can pull all your spark plugs and look for one or two that look dramatically different than the others. If you're leaking alot of coolant, people have diagnosed a bad headgasket by pulling all of the spark plugs after a hot shut-down and then holding a pieces of colored of paper (that easily shows presence of a liquid) over all plug holes. Then disconnect the coil from the distributor (so there's no spark) and crank it over. If water spray comes out of a specific spark plug hole, you'll know which of the two headgaskets to replace (in a v6 or v8). When the ECU sees no spark, it should disable the injectors, so you'll know it's not gas.
A compression test could also help diagnose a bad headgasket.
