I have a 2003 S-type R and I have been having problems with the heat. Anywhere from 72 mild heat to 85 decently hot I doesn't stay hot, it eventually cools down, no matter how high I set it, it's very intermittent and doesnt consistently blow heat, majority of the time its ambient to cool air, anybody have any ideas?

 

I would suspect the AUX coolant pump. It is on the passenger side of the radiator below the DCCV. First I would check the coolant level. Also does the engine temperature look and act OK?
The symptom is usually good heat at high speeds but poor to no heat at low speeds or stop and go traffic. With the car stopped try raising the engine speed to 2000-2500 rpm's. Hold it there for several minutes with the heater running. Do you get heat now?
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