So a few day ago, the heat in my 2013 g37x started getting cool. First starting the car, and the first half hour driving, it was hot as can be at like 75. I noticed it started getting cooler, turned it up to 77-78, it was hot again, then started to get cool. Every time it started to get cool, id turn it up, it would get hot, then start getting cool. If i shut the car off for a short time and get back in, it does the samething fairly quick. If it sits for a couple-few hours, it will work great for a half hour or so. It seems to not matter whether its city or highway, it acts the same. The coolant level is good, the temp guage is stable. No overheating or temp dropping. Not sure what the issue is. Was thinking a door blend actuator or the control module, but they seem to be working.

 

Hello:

You've described that the air being blown in via the HVAC is not hot, but the door blend actuator only controls how much air is let into the cabin, not the temperature of the air. Have you checked/replaced your thermostat? Heat is supplied to the cabin via the hot coolant from the thermostat into the heater core, and if the fan is working in the heater core then your thermostat probably needs replacement.

How a Car Thermostat Works

Good luck!


Rick

 

Im familiar with how the heat is made and gets into the cabin. Reason im not convinced its the thermostat, the air does get hot, and stays hot for awhile. It only starts to get cool after 30-40mins, regardless of city or highway driving. If the thermostat was stuck open, i dont imagine it would get as hot as it is, then cool down after awhile. Usually when the thermostat is stuck open, it doesnt get as hot, and doesnt get to operating temp, since the coolant just keeps circulating. It doesnt stay in the engine to cycle hot coolant out and cold/cooler coolant in. The coolant temp guage gets to full operating temp and stays there. Its almost as if a sensor thinks the temp in the cabin is getting too hott, then allows cool air to come through to cool the cabin down. Its not set on auto though.

 

Thermostats can stick open, close, or just stick. It's fairly quick to replace. If the car is on manual (non-auto) heat I wouldn't expect the air temperature to vary unless the coolant temperature is varying. Remember that your engine temperature gauge is heavily buffered in the mid-range.

You might want to check these videos:

Generic: Nissan-specific:
That assumes of course you have no codes.

Good luck!


Rick

 

I know how to replace a thermostat, i have done a few of them. I do have a fair bit of automotive experience. Whats throwing me off/why i dont think its the thermostat, one it gets so hot and stays hot for so long, but once it starts blowing cool, when i turn the heat up, it does get hot again, stays hot for a few minutes, then gets cool, can turn it up again, itll get hot, then itll cool. If it was the thermostat, one would think once it started to get cool, it wouldnt get hot again when you turn it up. It doesnt get hot on its own, if you leave it at say 75, once it cools, it stays blowing cool until you turn it up. Its acting as if its stuck in auto mode, eventhough its not in auto.

 

Sorry, in retrospect I don't think I was very clear. ave you looked at the two videos? Neither was about the thermostat, both were about recalibrating the climate control and door blend actuator. I think there are still cases where it may be your thermostat, but the two videos I sent were directly to offer an option that may address how the climate control is reacting without changing the thermostat.

Good luck!


Rick

 

i skimmed through one of them as i was in the middle of something at that time, but it seemed like it was only for recalibrating door blend actuators, and didnt seem to appear it would work for my car as it didnt have the same buttons/set up, then i forgot to watch to go back to them later. Ive also never been a fan of scotty kilmer 🤣 i will try the resetting a climate control and see if that works.

Sorry, my mind has been all over the place the last couple weeks. when this problem started, i was actually bringing my 13yr dog to the vet for xrays a couple days after getting lab results back. Found out shes anemic from internally bleeding. She has a tumor on her liver, and one on her spleen, and thats the one that was leaking/causing the internally bleeding. Ive havent done much of anything after work except spending time with her, cooking for her, and just trying to keep her as happy and as comfortable as we can until the unfortunate moment when the tumor ruptures and kills her. Shes been an amazing, super fun, super loyal dog, huge part of my life and my side kick the last 13yrs, so its been really tough. Shes a tough old girl, she still seems to more good moments than bad now that shes on meds to stop/slow down the bleeding, so it doesnt seem like its time to put her down yet. Im dreading that moment more than anything. She will be the 3rd dog we've had pass within 2 years. The last one was may or june from liver cancer, he was 11. the previous, his littermate/sister was January 2024. She was seemingly pretty healthy, i went out for a couple hours, came home and she was dead, she 10. Now the first of the 3 we got within a year is on her way. Its always such a tough thing to go through. But anyways, thank you for your help and bearing with me. Once i try the reset i will post back how it goes. Thanks again