so my 04 350z overheated yesterday, upon pulling over the only problem i found was back pressure in the reservoir since there was a crack the tank cap and i had a leak out of the overflow. i also lost all heat from the heating system in the cabin. i replaced the thermostat which still has not fixed the problem since the thermostat seems to be staying closed. inbound hose to the heater coil is getting extremely hot but outbound is staying cold so just wondering if im correct in assuming that its either 1. water pump 2. clog in the heater coil/ leak in the coil or 3. air in the system? any other suggestions or help would be great as im obviously wanting to start from cheapest to most expensive fixes.

help would be greatly appreciated thanks everyone

 

Air in the coolant system. Burp the system and you will have heat and no overheating issues.

 

It's always air in the system, except when it's air in the system.