Z overheating

[trandana]

Hey guys,
In this summer heat my z32 TT has been overheating especially on hills. I have noticed that I could drive perfectly fine on
the highway if it was level, but as soon as I hit a hill it the temp gauge starts to climb.
Before I start replacing parts trying to see what the issue is I would like to start in the right place.

The water pump was replaced with a OEM one 4 years ago (25,000 kms ago)
The thermostat was changed for a Nismo thermostat 25,000 kms ago
Has a Mishimoto radiator (7 years old) with a 16 psi rad cap
Has coolant line bypass


It has no coolant leaks and was just pressure tested 3 days ago.
My first thought is a clogged coolant hose, in need of a coolant flush, or air bubbles in the cooling system

Any other suggestions?

Thanks!

[RED_DET]

I would presume air in the cooling system.

[trandana]

Also, after I fix the overheating issues, I have been looking at possibly getting a 25 row oil cooler and a SARD high performance radiator.
How much of a decrease in temperatures might I get from these?

[NolimitZ32]

You wont get a decrease in engine temps unless you change your thermostat which isn't recommended because the engine is designed to run at a certain temp (non track dedicated). You will get more efficient cooling but I can't really quantify it for you maybe someone else can. As for the overheating issue I am with RED, you need to park the car on a level surface and burp the system with the car running and heater on full blast.

[RED_DET]

As previously mentioned, for a daily driven car and even spirited driving, the upgraded oil cooler and radiator won't change things. Track use, then we are talking about a different story and even then the OEM components if cared for properly and good condition will do the job.

[RubyRed300ZX]

The uphill issue is most certainly air in the system.

As for thermostat temp, I believe the Z uses a 170 or 175 degree temperature thermostat. Some previous owner may have replaced it with the more typical 190 or 195 degree thermostat common to other car manufactures. Though it's also possible it was installed upside down with the jiggle at the bottom (meaning it needs to be clocked 180 degrees).

[trandana]

So I learned today that I havn't been bleeding air out of the cooling lines properly lol
but I also noticed that the AC fan is completely broken and never turns on.
On days like today where its very hot out, regardless of wether or not the AC is on, that fan should be coming on and its not.
And On days like today under these conditions is usually when it overheats. And it was today. could it be that the car is trying to
turn that fan on and its not, causing the car to overheat?
I will be replacing that fan, but in the meantime I bled the lines properly, and there was definitely some air bubbles popping up. After a while they stopped coming up and the coolant leveled off and stopped going down.
I took it for a test drive and things were fine, until i turned the ac on and the temp started to rise, and worse when just idling in the driveway and car was getting less air flow. The temperature during the drive wasn't that hot, only about 17 Celsius. I shut the car off and I can hear a boiling/bubbling noise coming from the rear of the engine.
I'm guessing it's the coolant boiling or more air bubbles? I will continue to burp the air out each morning, but could that ac fan/motor failure be the main cause?
Also, I know these are symptoms of a bad fan clutch, but when spun by hand it only rotates about a half spin or less.

[trandana]

So I took it to Nissan suspecting the aux fan was the issue, and they confirmed that. They said that the aux fan was actually disconnected because it wasn't working anymore and vibrating like crazy.
The lazy previous owner simply disconnected it without replacing it. (Thanks for not telling me when I bought the car)
So im ordering a new one, hopefully that will solve it. All the air bubbles seem so be gone now.