Nissan Repair Questions? Ask a Mechanic for Answers ASAP
Hi There, This is Clay, I'm a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description most likely the heater core is leaking. What's the model of this 2004 Nissan?
Let me know.
All I can really do is speculate with out a model or at least an engine size. You can pinch off the heater hoses on the engine side of the firewall to stop the antifreeze from filling up the HVAC assembly under the dash. Once the heater core is blocked off it would be a good idea to do a Block-Check to make sure there are no exhaust gasses in the cooling system in case the vehicle has been run hot.