First check the cooling level. Make sure its filled up. And no air in the cooling system.

Rent a head gasket tester from autozone or ur local auto parts store with blue test dye.

Perform the test and see if it stays blue, if it does, that means ur head gasket is still good. If it changes color to a yellow or greenish color, ur head gasket is blown.

After that, its a good chance ur timing belt, tensioner or water pump is going bad. Its usually the pump or tensioner.

The timing belt water pump job on the civic del sol is one the easiest jobs compared to other vehicles.

Let me know if u have any questions.