Heater core not good. Can I still drive it?

Heater core not good. Can I still drive it? So my heater core is no good. I can hear the fluid and when I use the heat the windshield fogs up with an oily substance. But no leaking inside of vehicle nor any leaks anywhere. Can I still drive my car if I just don't use the heat and always keep the air to cold so I bypass the heater core. Can I still drive it?