Cooling issue from hell

[Chickenman]

^ Yes, same old story with " Global Market " parts. Even Stant aren't what they used to be. OEM Nissan thermostats are the only ones I will now use. Same on my GM's and Audi.

Stant ( and other aftermarket ) hysterious is way off. IE: Slow to respond to opening and closing temp differentials. . I also found that the Stant " Hole opening " size was substantially smaller than OEM Nissan. 

Changing to a factory Nissan thermostat would be the quickest and cheapest thing to try. Edit: Notice you stated that you had a new OEM Thermostat. Is that an OEM Nissan Thermostat? 

Of course the factory gauges are often inaccurate as well, So get a Digital thermometer as others have mentioned. 

A fan shroud will certainly help maintain cooling at idle. At idle the Fan does turn, but not at full speed. This makes operating without a shroud much less efficient. 

Edited June 28, 2017 by Chickenman

[Chickenman]

Just as a reference point. I have a 1976 280Z NA.  3 core custom Copper Rad. New 180 F Nissan Stat, New OEM Nissan W/pump.  Factory 8 Blade Fan and Shroud ( 280Z AC fan ).  New Thermo-clutch ( Hayden ) Redline Water Wetter.

Temp Gauge normally sits in middle of the " E " in Temp. Stop and go traffic. On the Hwy it will drop to the left end of the " E " ( 60 to 70 F ambient ). With AC on, stop and go traffic at 90 to 95 ambient, gauge went up to left hand leg of the " M ". That's pretty darned good.

BTW, just got back from a 600 mile Cruise through the Cascade mountains and Okanogan desert region. Car ran as cool as a Cucumber even though it was stinking hot outside and AC was going full blast all the time. 

I should add that this is on a freshly rebuilt block and head that had been cleaned a High pressure Steam cabinet. There was absolutely no rust or scale in any internal water passages. So that has to be taken into account. FWIW. 

Edited June 27, 2017 by Chickenman

[siteunseen]

3 hours ago, Reptoid Overlords said:

Same thing happens to my ZX, gauge reads a touch high, but meat thermometer produces numbers within spec. When I first got it, it ran way hot. I decided to put the fan assembly from my parts car on and the temp went down in all conditions. One thing I noticed after switching fans was an audible fan noise once temp was reached that wasn't there with the original one. Do the early cars make that same noise when the fan is engaged?

I say that's the fan clutch but without a little more info I'm just guessing. The way I've always thought/learned when the car is cold you should only be able to get one or two at the most rotations of the fan by spinning with your hand. I've also read where they somehow lock up and spin continuously sounding like an airplane all the time.

[Patcon]

My best guesses. Head issues, bad temp gauge. Did you bore the engine? If the cylinder wall thickness gets too thin you can over heat problems...

[siteunseen]

I'm leaning to the timing adjustment just for shits and giggles. Also I can dial my potentiometer while driving and watch the temps go up and down. So maybe cleaning those connections might have an effect? 

[Zed Head]

5 hours ago, Z3P0 said:

the temp on the temp gauge reads too high for my liking. Looks like it's reading about 200-210 and my fan clutch is not kicking on. At start up it does but the coil doesn't hold up to help the fan pull air. This happens at idle. While I drive at highway or even regular speeds the temp goes dramatically down and stays at regular about halfway. But when the engine does overheat it stays at the temperature stated above. That tells me that my thermostat is working but it still over heats. I need help.

A thermostat that's stuck open will behave this way.  Coolant flow isn't controlled so overcooling happens at freeway speeds.  But it wouldn't cause temperature to go high.  Not enough air flow would though.  So a stuck open thermostat and poor air flow kind of fits the symptoms.  The thermostat STOPS flow it doesn't cause it.  The thermostat is there to increase engine temperature.  People get that backward often.  So the signs actually show that the thermostat might not be working properly.

If the head gasket is bad it will typically overpressurize the system, from leaking exhaust gases, causing fluid loss.  If it's an air flow issue, opening the hood typically has an effect.  

Here's something that I don't think was mentioned - is your heater core bypassed?  That can cause overheating by lowering the coolant flow through the block and head.

[Chickenman]

The fact that the new Thermal clutch fan is NOT engaging, at what you figure is 200 to 210 degrees is an indication that the engine may not be running as hot as you think. At this point, I think I would buy a decent Mechanical temperature gauge and temporarily plumb it into the system so that you can get some factual data while actually driving. Factory electrical Temp gauges can be  notoriously inaccurate as already mentioned. Certainly a conundrum...  

Edited June 28, 2017 by Chickenman