What are the symptoms of a blown head gasket?

Answer

Blown head gaskets will most commonly cause a loss of coolant (anti-freeze) and as a result overheating of the engine. Another sympton could be water leaking into the oil which will give the oil a coffee with milk type appearance although this is much less common.

Addendum:

Also on the Chevy Venture a head gasket leak can develop such that exhaust fumes are pushed into the coolant system - the coolant will be displaced and expelled, first via the coolant reservoir then the van will overheat and dump the coolant right out of the pressure relief at the cap.

To test for this particular leak: when the engine is cold, remove the radiator cap, then start the vehicle. If coolant immediately start pouring from the top of the radiator, this could well be your problem.

I had this problem on my 2001 Chevy Venture and researched it on auto forums and found the answer in an obscure location. Just had the head gaskets replaced (along with the intake gaskets since this is also a common problem on these beasts) and everything is now good.

Answer

oil in the anti freeze
NO, IT'S ANTI FREEZE IN THE OIL.

Open the cap on the coolant overflow tank and smell the contents. If it smells like oil/gas or if the container is coated with a black oily residue on the inside, that equals blown headgasket. With the Subaru 2.5 engine, this is the most common scenario. The engine will usually run fine, but overheat often.
2 adjacient cylinders low compression White smoke (steam)from tailpipe when engine at normal operating temperature Coolant mixed with motor oil Motor oil mixed with coolant Run engine to normal operating temperature remove dipstick and let a drop of fluid drop on a hot engine part Oil will smoke coolant will sizzle