Overheating issue

[socrates60]

Here we go again. As I stated in previous posts when I had the engine rebuild done I opted for a dual electric fan setup with the "upgraded" NA radiator from Z1. The car did fine while the weather was cooler, but now that we are in the HOT summer down here in SC I'm having an issue with car running hot with the A/C running. After driving around for about half an hour the temp gauge will creep up to around the 3/4 mark. It doesn't go any higher, and if I turn the A/C off the needle will go back down to slightly below halfway.

My mechanic seems to think that despite the upgraded radiator from Z1 it may not be doing the job of cooling; his suggestion is to put in a Mishimoto TT radiator with the bracket from Z1 that takes care of the mounting issues. I've read all the posts about the downside of the electric fans but he still thinks they will do the job. I really don't want to go through the expense of changing over/back to the stock fan clutch/fan setup.

Just wondering if anyone has any input on this. Through him I can get a pretty good price on the Mishimoto radiator and the bracket cost from Z1 is minimal. The cost of going back to the stock setup is quite a bit more.

Thanks in advance.

[nissanfreak12]

You need to find stronger fans. You will still overheat with those electric fans and the mishimoto radiator. The condenser creates so much heat, you need a strong fan to pull the cooler air through it and the radiator.

Electric fans are great, they just need enough CFM to do the job. Below are a couple fans that will do the job because they are 2 speeds and have a better pitch than smaller universal fans.

Taurus SHO Fan
Mark VIII Fan
MIshimoto Fan(this is still iffy by some owners)
Maxima Fans
Jeep Grand Cherokee 5.9 Fan(same speed as the SHO fan)

There are more, but these are ones off the top of my head. Most require modification to fit, except the maxima fan. Its a direct fit to a NA radiator.

[socrates60]

Thanks for this. Just wondering--I know you said the Maxima fan is a direct fit for an NA radiator, but right now my plan is to put the Mishimoto TT radiator in the car. What about the fit for that, or do you recommend one of the other ones? Would the Mishimoto fans be a better option? It seems like when I was looking on the Mishimoto website their electric fan setup for a TT was just a single large fan versus the dual ones I have now from Z1.

One other thing--on the Maxima fan are those from particular years of Maxima's? Like the early 90s models?

[DCaff300ZX]

Let me throw this out there- perhaps you are missing one thing. I fought a cooling issue due to slow air infiltration into the cooling system with my NA for about 2 years, that despite all efforts persisted until eventually presenting itself as a leaking heater core. Crud from years of circulation of coolant from the rad settles in the lower end of the inner cores in the middle near the spout out, plugging it enough to inhibit flow and adding a catalyst for corrosion of the core and finally a leak that explained how air keeps getting into the closed cooling system and causing the creeping heat levels that shutting down peripherals will often help up until the leak finally presents on your tunnel carpet. Another possibility for air infiltration is a bad rad cap (fairly common), and not bleeding the system for air or incompletely due to rad replacement with a non-OEM rad with no upper bleeding screw setup. The correct bleeding procedure is very important for the Z32: running the fan on high with the rad cap off and full of fluid, as the engine reaches temp ensure no bubbles or pulses and full condition then cap the rad, then open the bleeder screw on top and being aware of the spinning fan, pinch the upper hose until coolant JUST hits the top of the bleeder hole (ensuring no air in system) hold 6 seconds and recap the bleeder. This ensures circulation through the core and system and NO air in the coolant...if problems occur again check for air. When safely opening the rad cap later you should have fluid right there and no air space...if air space, you have a small leak in the core, or core hoses most likely, or pin leak in the rad or even possibly corroded core hard pipes.
Use a pressure test and check for a longer period of time (when hot, and until completely cooled) and check for ANY change- my leak was so small I'd only on a few occasions ever smell coolant in the cabin, and despite the cooling problem and efforts to fix it never suspected the core until it leaked onto the floor.
As for dual electric fans and sizes and all, I myself and my Z mechanic do not believe in the dual electric fan setups and the fact Mishimoto only uses one shows that air flow is generally not the issue with Z32's, it's radiator air flow blockage (FMIC, other), air in the cooling system, and/or incorrect tuning setups that more often cause/lead to cooling problems rather than even the stock clutch fan- my 400+ HP tuned Z runs cooler than stock on a complete OEM cooling system (actually still has it's original clutch fan), always, no matter the outside temp (been out in 94 degree heat for hours) and I actually need to find a way to add about 3-4 degrees of engine heat for best idle and low end operation- so I really doubt your issue is with cooling fans and fan size/output.
Hope this helps!

[socrates60]

Thanks!! I'll certainly look into this.

[socrates60]

I need some input from all of you much smarter guys about the overheating issue. The car has had the Mishimoto radiator and the Mishimoto TT fan installed in it(the car's an NA), but I am still having an overheating issue. The latest problem is this--after driving the car for about half an hour with the A/C on and running the temp gauge never went above the halfway mark, but as soon as I turn the A/C off the gauge shoots up to the top. Shouldn't the needle start going down when the A/C is shut off? It's only the middle of August here in SC and we still have a lot of hot days left to go, and I don't relish the idea of having to drive around with no A/C. I did drive the car this morning for about 45 minutes with the A/C off and no problems.

[nissanfreak12]

Could somehow the electric and AC are connected so when you shut off the AC, the fan shuts off? Do you still have the front e-fan still attached that came from the factory?

[socrates60]

nissanfreak--no, I checked that; the fan will still stay on when the A/C is shut off until the car cools off enough for it to shut down on it's own. From what I've observed without the AC running it will kick on when the temp gauge hits about the halfway mark. As for the aux fan, it's still there. It's actually set to come on whenever the AC is turned on, not to wait until the coolant reaches the specified temp. I drove it this morning around town (it's still pretty warm and humid) with the AC running, then shut it down when I got back home and parked. The needle stayed the same, about halfway, and I let the car run for awhile afterwards just to see if it would creep up--it didn't.

[DCaff300ZX]

It could be due to the aux fan, which does do some good work when it is deployed but as noted, normally only does so when the AC is turned on and temps rise.
I can only speculate, but increased fan output if yours is wired to run constantly and then is turned off might cause a spike of temp for a minute or so, but I'd assume it wouldn't pin the temp gauge...very odd, especially if as your latest post mentions nothing went wrong the next time out.
Have you double/triple checked the rad for ANY air? Done pressure checks, long term ones waiting an hour or more for pressure changes? When my NA's heater core finally went out it had been an on and off temp spike situation for months, often with long stretches of no temp spikes but then suddenly they come back after enough air got in, and a hotter day/longer drive.
With the fact nothing obvious is showing, only thing left to do is double/triple checking things and more detailed tests...the bane of the Z32 IMO.

[Mishimoto]

I need some input from all of you much smarter guys about the overheating issue. The car has had the Mishimoto radiator and the Mishimoto TT fan installed in it(the car's an NA), but I am still having an overheating issue. The latest problem is this--after driving the car for about half an hour with the A/C on and running the temp gauge never went above the halfway mark, but as soon as I turn the A/C off the gauge shoots up to the top. Shouldn't the needle start going down when the A/C is shut off? It's only the middle of August here in SC and we still have a lot of hot days left to go, and I don't relish the idea of having to drive around with no A/C. I did drive the car this morning for about 45 minutes with the A/C off and no problems.

hey Socrates60,

Thank you for the post.

If you are having any issues with one of our products, we will be happy to assist you with troubleshooting and resolving the issue.

Feel free to contact us directly at [email protected] so we may better assist you.

Best Regards,
Mishimoto