Hoping that someone can provide some insight on this one. I replaced the water pump and the thermostat (cleaned the intake valves at the time as well) on my wife's Cayenne in April 2020. I had the coolant system pressure/vacuum bled by a shop that I trust, and the car has been running without issue for the past year. Recently, the CEL came on, the code of P0599 is showing up, and the car is overheating when pushed on the highway. Temp stays at 201F when idling and when driving around normally, but I can get it to climb to the 220+ range, if I accelerate hard on the highway.
I checked, and it doesn't look like this car has the solenoid actuated shutters for the radiator. I don't believe that it has the solenoid actuated water pump, either. There's nothing clearly blocking the radiator in the front. No coolant loss, and no milky oil. I'm honestly at a loss on this one, and hoping someone has some advice, before I just throw a thermostat at it and hope for the best.