Q: Heat Only Kicks In At Higher Speeds on 2003 Nissan 350Z

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The only way my heat will come on is if I punch lower speeds or without gunning the engine, I have no heat whatsoever. Does anyone know what this signifies or what the repair would entail?
(1) Answer
Customer Concern: When at cruising speed, would have heat. When came to a stop, the air temperature would cool down.
Tests/Procedures: 1. With the car fully warmed up and idling, raise the front of the vehicle in the air and check to see if the heat returns in the car. Check for an air pocket in the heater core if the heat returns.

2. Check the coolant protection level. If the coolant has recently been replaced, try thinning the mixture of the coolant. Add a little more water to the level.

3. Check the heater core for a restriction by using a water hose and attaching it to the heater core. The heater core should flow water very easily and water should not be spraying from the hose (if it did, that would be indicating resistance to flow).
Potential Causes: Incorrect Coolant Mix
Aerated Heater Core — Air pocket in the heater core.
Restricted Heater Core

Tech Tips: There have been a number of Nissan and Infinity vehicles that will not blow heat at idle. In many cases this happened after service work was performed, and draining some of the coolant and adding water would fix the problem most of the time.