Exhaust in my radiator

[Randberg at aol.com]

My son was driving my '89 100 when it overheated and water began leaking into 
the drivers and passengers shoes. The car quit so we let it cool and drove it 
hone 10 miles, the next day. I figured it blew the heater core so I 
disconnected the heater hoses under the hood and hooked them together. The 
car starts, runs but there is exhaust in my radiator reservoir. Do I have a 
blown head gasket, or is it the steering wheel nut (The nut behind the 
steering wheel - ME). I am 2 seconds away from trashing the car but I really 
like it. ANYONE???