Chevrolet Lumina Radiator Cap

I Put A New Water Pump, Thermostat, Rad. Rad, Cap.i Came Home Sat.2:30 And Sun. Morn. I Went Out To Check The Rad. And It Had Pressure In It...

Just Changed Thermostat And Radiator Start Car And Coolant Leaking (forced Out Under A Lot Of Pressure) Around Radiator Cap And Bottom Hose...

Heat Gauge Will To Hot Almost To Red Line For Shot Time Then Back To Normal And Runs Fine The Rest Of The Day.this Happens After Car Sit's...

There Is An Oily Sludge That Collects On The Radiator Cap Over A Period Of 4 Days Or So. The Oil Looks Low On The Dipstick But No Foam Or...