The dipstick blows out because you have too much crankcase pressure, (not to be confused with oil pressure). This pressure comes from the combustion process, you know, when the gas ignites. Some of the gasses ALWAYS leak past the piston rings into the crankcase. This is called 'blowby'.
You have too much blowby. It may be time for an engine rebuild.
The holes on the rear of each valve cover (about this size of your finger) that have a hose on them that 'Y's into the pipe on the throttlebody is what helps 'relieve' that pressure.
Those hoses may be plugged, and/or the passage into the throttlebody may also be plugged.
The pressure MUST be vented out.
http://www.cygnusx1.net/supra/librar.../ec/EC_05.html
Carb spray, coat hanger, drill bit, bottle brush, etc. You figure it out as you go.