sounds like the radiator is clogged and has overheated the motor to the point that the head gasket has failed.

Roy

Do you have to add water often?
Additionally, have a shop to test the cooling system for the presence of combustion gases, a sign of a blown head gasket or warped cylinder head.
You can do the test yourself, but the test strips can be expensive in some locations. In someplaces you can order them from your local autoparts stores in small quantities for around $10. Other places you'll have to buy them in large quantities for around $75 (so its just a matter of how inexpensively you can get the test strips). The tests are easy to do, just follow the directions on the package.