Car quickly overheating

1993 Pontiac Bonneville, 180,000 miles.
Hi guys, recently have started having problems with my pontiac with overheating to temps of about 240-250 with only about 3-4 minutes of city driving. It also has started blowing white steam under the hood when it hits these temps. When I check under the hood, the radiatior and coolant container both do not appear hot as if you could take the radiatior cap off without burning yourself, yet, when I feel the block it appears to feel hot. Also, the steam seems to be coming from the bottom of the car and not exactly from the radiator. It has taken 3 gallons of antifreeze in the past week and will occasionally start to make a "boiling" noise and radiator fluid will boil out after the car is stopped. Any help you guys could give would be greatly appreciated. Thanks.