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ZackZ420 06-13-2018 08:10 AM

This has probably been posted before and I'm sorry, but my Z will get really hot really quick. If I'mkm driving it around it will be fine but when it is jus sitting at idle it will warm up. Then when it gets to 185 it will just keep getting hotter till it goes way past 220. And I noticed that my second fan doesn't come on. Even when I put the a/c on, which doesn't work anyways. Is it a faulty coolant sensor. System had rust in it. I flushed it 4 times with thermocure cleaner. I'm still scratching my head. Any thoughts?

PaulyC 06-13-2018 05:54 PM

Re: Overheating
Is your primary fan turning on? There are a couple of things to check here. First we can assume the thermostat is at least open and flowing or you would have an issue even when driving. So that points us to airflow which we are getting when the car is moving. If your primary fan is turning on I am suspicious the thermostat is sticking open. If your main fan is not turning on then we need to test the Fan fuse, relay and fan. The 1991 primary fan VIN F & VIN 8 is controlled by the ECU, which grounds the relay coil to turn the fan on. You can test this by grounding the Grn/Wht wire at the relay.

ZackZ420 06-13-2018 05:59 PM

Re: Overheating
Yes my primary (drivers) side fan turns on. But not passenger side and it gets hot and it even boiled over into reservoir

PaulyC 06-13-2018 06:45 PM

Re: Overheating
The secondary fan will turn on without the ecu and AC with a temp switch from the factory that will close at 238 degrees. If the temp is going above that then test the secondary fan circuit. You can jump the temp switch connector and second fan should turn on. If it still does not then check the relay, you can make a jumper wire and jump orange and blk/pnk at the relay connector which will bypass the relay. The orange is hot in run, jump it with the key off then turn the key on and the fan should start right away. The temp switch is located in the head between #6 and #8 cylinders.

If you get both fans running, still suspect the sticky tstat. Couple more things to consider there is a possibility we could be looking at a pump issue as well. If the coolant was real dirty the pump vanes could be dirty as well to the point of being inefficient at low speeds. You can try to bring the rpms up a bit while sitting still and see if it has an effect on the temp rise. This should go without saying but make sure the coolant is topped off.

ZackZ420 06-15-2018 06:11 AM

Re: Overheating
And if it is a pump issue, what kind do you perfer? Ac Delco or gates?

PaulyC 06-15-2018 06:27 AM

Re: Overheating
I’ve never had any issues with either of those two brands. I personally use AC Delco for stock part replacements whenever possible.

TallTim 06-15-2018 03:44 PM

Re: Overheating
Is the radiator cap good meaning building pressure? Having a spare is cheap insurance.

Is the rad in good shape (lots of bent fins, maybe old or corroded).

Is there junk in front of the rad?

2nd fan comes on around 230. Remove the wire from the pax side sensor and ground it, fan 2 should come on.

pfsteichen 06-22-2018 09:27 AM

Re: Overheating
My 92Z 305 runs too hot too fast. My air dam is in place and I'm not losing any coolant. Fans are on a switch. My radiator and water pump were supposedly changed by previous owner(I've driven car for 6 years) I turn the fans on when it heats to just over 200. I would like to be able to use my air but not now. Thoughts on what I should check?

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