2012+ Coolant System/Overheating

PogiFlip

Hey guys! I've tried researching everywhere and there doesn't seem to be a thread specific to the issue I'm having.

Issue/Background: It all started this summer when I noticed my A/C would turn off by itself after some normal driving and then idling. This would happen usually on hot days here in AZ. My coolant temperature would gradually increase after 10-15 minutes idling. On really hot days (116 degrees per the car), the same coolant temp increase would happen WHILE I'm driving on the freeway going 75-85mph. All this would happen while the AC is on. With AC off, the temperatures are normal. Temperatures would usually max out one or two dots before the "H" and the AC turns off to protect the engine. From there, with the AC off, the coolant temps would decrease at a faster rate (versus the increase I've experienced) and the AC would come back on and the cycle repeats. With the idling scenario, driving after idling would decrease the temps to normal. After I turn off my car, I would hear some gurgling inside the cabin coming from the engine. This turned out to be bubbles from the coolant system which believe is a result from coolant moving from the engine back to the expansion tank.

I've attempted to use a lisle coolant funnel to burp the coolant multiple times and the same gurgling and bubbles is still present regardless of all the attempts. Maybe I'm supposed to burp from the expansion tank? I finally tried to seek help from a reputable shop here in AZ specializing in Nissan/Infiniti and the mechanic believes that the source of the air bubbles/leak was coming from this small hose on the driver side with a loose clamp so he tightened that out. The mechanic noticed that the coolant system was different from other cars he worked on and figured that around 2012 Nissan decided to go with a modified coolant system where the reservoir tank is pressurized and sealed along with the rest of the system and the reservoir tank is now an expansion tank similar to what BMW utilizes. There is an extra hose connecting from the bottom of the tank to the engine/coolant system. Also, the cap on the reservoir tank is pressurized as opposed to the radiator cap located more near the engine. I learned the hard way by trying to fill coolant from the non-pressurized cap and noticed my expansion tank was filling up to full instead!

The coolant levels are fine and stays at max when the car is cool. Coolant is OEM Nissan blue. I replaced the non-pressurized rad cap and that didn't help. Mechanic says the pressurized cap is fine, especially the car being fairly new. Coolant system is OEM except that I was told the coolant system is connected to my turbos to cool them. The heater immediately pushes good heat when turned on. The previous owner confirmed that the gurgling happened to him but the overheating never did. He told me that a lot of people ended up using the OEM radiator because it works fine without issues and AC functionality. I didn't confirm if he was referring to FI people or NA. He actually looked into installing a CSF radiator but the AC didn't work right and it leaked everywhere so he decided to stay OEM thinking AC is a must in AZ (and I agree)!

The shop I went to is leaning towards aftermarket radiator and fans, he noticed that the coolant temps stayed the same and when you turn off AC the temps shoot straight down suggesting not enough rad fan pull to cool the car. The previous owner suggested looking into the Ecutek tune but the mechanic said the tune looks ok because he noticed that the fans are kicking earlier than OEM temp thresholds and high/low fan speeds are working fine. He also said that the coolant system I have with the expansion tank should self-bleed itself since the reservoir tank is connected to the system and the bubbles should leave by itself which it did when we bled it at the shop, so no vacuum fill occurred. He didn't check the pressure in the system because he was fairly confident it was the loose clamp. Per the mechanic, the hose itself showed dried blue coolant and the leak wasn't apparent because it would drop on the heat sheild above the turbo and evaporate before hitting the floor.

So far, it doesn't seem like the resources local to me know what's happening exactly and so I've come to the forums for some assistance! I apologize for the lengthy post. I appreciate your time in reading and responding to this thread! Thank you so much!

Questions:
1. Is anybody familiar with this newer coolant system? Is the gurgling or moving of coolant from the engine to expansion tank normal for this coolant system after turning off the car?
2. When burping the coolant system, should I do it from the expansion tank instead of the other cap location closer to the engine? This was suggested by my mechanic.
3. Any help/ideas about the overheating issue?

Vehicle:
370Z 2015 Nismo
Fast Intentions Twin Turbo System
GT2860RS Turbos
2 Tial Q 50mm BOVs
FI Front Mount Intercooler
Greedy Oil Pan
Bosch 1000cc Fuel Injectors
Ecutek Flex Fuel Tune by SpecialtyZ
Walboro 485 Fuel Pump
Setrab 34 Row Oil Cooler
FI Front Tow Bar