2011 Cayenne S - P0599 Thermostat Heater Control Circuit High

[e36M3to996]

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.

[JFP in PA]

Welcome to RennTech 

 

Thermostat may have failed; I would check the hose running from the engine to the radiator when the car is running and warmed up; if it is cold, either the thermostat is stuck, or radiator is blocked.  You can check the radiator for blockage by using a non-contact pyrometer to see if some of it runs cold or cooler when other sections are hot.

[e36M3to996]

26 minutes ago, JFP in PA said:

Welcome to RennTech 

 

Thermostat may have failed; I would check the hose running from the engine to the radiator when the car is running and warmed up; if it is cold, either the thermostat is stuck, or radiator is blocked.  You can check the radiator for blockage by using a non-contact pyrometer to see if some of it runs cold or cooler when other sections are hot.

Appreciate it. I actually had to look back at my profile, as I saw this was my first post, but I've been lurking on here for over 10 years. Been a great resource, I should really contribute. 😉

 

I'll check temps across the radiator, but I'm fairly confident that the thermostat is opening at least some of the time, as it doesn't overheat when idling, and temps were in the low 90's, last time I let it sit. Really annoying, as it's one of those intermittent issues.

[deilenberger]

Did you use a Porsche water pump?  It sounds like a loose impeller or otherwise failed water pump.  Able to circulate enough coolant when idling, but not enough when under load.  Thermostats generally (not aways but usually) fail open.  And how are you reading the coolant temperature?   Hopefully not by the heavily buffered coolant temperature gauge - that's about as useful as an overheat-idiot light. If it reads hot something is really wrong.