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RESOLVED: Cooling System Troubleshooting

Old 03-16-2019, 02:06 PM
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RESOLVED: Cooling System Troubleshooting

Hey ThirdGen'ers!

While idling, I noticed that the Temp Gauge went up past the 220 mark but no Cooling fan. When the car reached the 3rd line, before the red zone I shut her off. There was no gurgling or boil over in the overflow tank, physical radiator was just reaching luke warm to the touch at best, and I could hold the upper rad hose bare handed. Grabbed the GMSM, used a fused jumper wire between the RED wire & BLK/RED wire terminals on the Fan Relay connector, fan came on instantly. Two questions...

1. If the Temp Sensor for the gauge is shot, can it show a false overheating condition and the motor not really be at operating temp to activate the fan switch? If it's wire from the connector is resting on a spark plug wire will it cause resistance issues leading to a false reading?

2. If anyone has ever changed a Radiator Fan Switch on a 92 or similar w/ 305 TBI how did you access it? Tried from below, but there were to many obstacles... Couldn't even reach the connector to disconnect it to attempt grounding it for further troubleshooting...

Last edited by 92RS-HeritageEd; 05-21-2019 at 09:30 PM.
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Old 03-17-2019, 12:54 AM
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Re: Cooling System Troubleshooting

on q1. part a - sensor is unlikely to fail safe. in other words, unpredictable. q1 part b, remove off wire and find out. but i would doubt it. most sensors operate over a voltage range that is converted to a reading. spark plug wire would cause a frequency reading issue if anything
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Old 03-17-2019, 06:53 AM
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Re: Cooling System Troubleshooting

My buddy has a 92 Z and his acts the same way. the fan does not come on until 240! The Other fan only comes on when he turns on the AC. GM programmed these cars to kick that fan on @ 235. I believe. His car does get hot, his gauge is accurate. I really don't know how that thing has not blown a gasket by now.

When I was having issues with my cooling system I purchased, for $5 on sale @ HF a inferred temp sensor, one of the laser ones. You can use it to get the temps of the head, rad hoses and the radiator itself. This will tell you if your temp gauge is working or not. That gauge may just be your only problem.
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Old 03-18-2019, 09:02 PM
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Re: Cooling System Troubleshooting

Anyone know how to remove the connector from the Fan Switch? It *looks* like a push-on connector BUT it did not simply pull-off and I do not want to damage it.
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Old 03-18-2019, 09:04 PM
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Re: Cooling System Troubleshooting

If it’s the factory connector squeeze and pull. The connector gets brittle with heat. If you need a new one here’s a link.
https://www.ebay.com/itm/Knock-KS-De...AAAOSwd9Za6d2k

Last edited by Tuned Performance; 03-18-2019 at 09:07 PM.
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Old 03-18-2019, 09:52 PM
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Re: Cooling System Troubleshooting

clean it off and put a strong light on it. you will see how it is anchored and what you need to do
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Old 03-21-2019, 07:34 PM
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Re: Cooling System Troubleshooting

Originally Posted by Tuned Performance View Post
If it’s the factory connector squeeze and pull. The connector gets brittle with heat. If you need a new one here’s a link.
https://www.ebay.com/itm/Knock-KS-De...AAAOSwd9Za6d2k
Finally got around to removing the connector, lt was the OEM connector and thanks to your instruction (as always) and LiquidBlue's suggestion of a shop light I actually got the connector off. Of course the plastic was brittle and had a chip in it but all-in-all it seems reusable. Next chance I get i'll slap the battery in it and ground the connector for testing. Hopefully the fan kicks on, then my issue will be a $9 fan switch vs a priceless wiring issue.
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Old 03-23-2019, 04:52 PM
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Re: Cooling System Troubleshooting

RESOLVED: Found out by moving the temp gauge sensor wire off of the #1 sp wire... gauge works as normal, a bonus is my cooling fan did come on in line w/ the correct gauge reading of just past the 220 mark!
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Old 05-24-2019, 08:55 AM
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Re: RESOLVED: Cooling System Troubleshooting

Is there somewhere on the forum some photos of the different sensors/switches from the cooling system ? I read a few topics about that but even if I'm starting to be familiar with the different elements of the system, I still don't know how they look like and where they are located on the engine.
I know where is the fuse box but it's almost the only thing I'm sure. I don't know exactly where is the relay (someone told me, I didn't have time to check right now), I don't know where is the fan switch or the sensor (sender) for the gage.

I think this is the fan switch and I'm supposing that in my case (similar to 92RS' case) it is faulty but I have to be sure that I'm looking at the right part and I must find a way to test it.


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Old 05-24-2019, 11:48 AM
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Re: RESOLVED: Cooling System Troubleshooting

Originally Posted by Flat-twin View Post
Is there somewhere on the forum some photos of the different sensors/switches from the cooling system ? I read a few topics about that but even if I'm starting to be familiar with the different elements of the system, I still don't know how they look like and where they are located on the engine.
I know where is the fuse box but it's almost the only thing I'm sure. I don't know exactly where is the relay (someone told me, I didn't have time to check right now), I don't know where is the fan switch or the sensor (sender) for the gage.

I think this is the fan switch and I'm supposing that in my case (similar to 92RS' case) it is faulty but I have to be sure that I'm looking at the right part and I must find a way to test it.

If I'm not mistaken... that's the AC High Pressure Switch you have circled. The cooling fan relay is on the firewall, driver side. I'll edit this reply with a pic shortly.



behind ESC Module thing in that bracket

Last edited by 92RS-HeritageEd; 05-24-2019 at 11:54 AM.
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Old 05-24-2019, 12:25 PM
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Re: RESOLVED: Cooling System Troubleshooting

Thanks for the relay pic Do you know where is that fan switch please ? I think that I located the sensor on driver's side head but I can't find the switch.
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Old 05-24-2019, 01:19 PM
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Re: RESOLVED: Cooling System Troubleshooting

Originally Posted by Flat-twin View Post
Thanks for the relay pic Do you know where is that fan switch please ? I think that I located the sensor on driver's side head but I can't find the switch.
Iirc, the FS is in the driver pass side head in the area of SP#4 and #6. The temp gauge sender is on the pass driver side by #1 plug

Last edited by 92RS-HeritageEd; 05-24-2019 at 04:04 PM.
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Old 05-24-2019, 02:39 PM
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Re: RESOLVED: Cooling System Troubleshooting

I thought it was the contrary (sender on drivers side and FS on passenger side).

And sorry about the next silly question but SP means ? (I'm not used to English initialisms yet).
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Old 05-24-2019, 03:34 PM
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Re: RESOLVED: Cooling System Troubleshooting

temp gauge "dash" is on driver's side, fan switch is on passenger side between 6-8 cyl near the manifold, the lower one is the knock sensor don't get these confused they look very similar
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Old 05-24-2019, 04:10 PM
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Re: RESOLVED: Cooling System Troubleshooting

Originally Posted by Flat-twin View Post
I thought it was the contrary (sender on drivers side and FS on passenger side).

And sorry about the next silly question but SP means ? (I'm not used to English initialisms yet).
My apologies, I was trying to help while on lunch at work so I was speeding through. BUT anyone who knows SBC's & their plug locations should have been ok. After all I did give the CORRECT physical locations... such as the gauge sender being by SP or Spark Plug # 1 which is on the Driverside, and the physical fan switch being by plugs #4 & #6 which is on the Passenger side. Also, as stated DO NOT confuse the Knock Sensor lol.
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Old Today, 11:32 AM
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Re: RESOLVED: Cooling System Troubleshooting

By the way, is there somewhere I can find the OEM part number in order to find replacements ? When I was working on my BMW we had something called RealOEM which allowed to find a part number based on schematics after entering the VIN (which would make sure the part fits the model, even if you have specific options). Is there something similar for the 3rd gens ?
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Old Today, 01:22 PM
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Re: RESOLVED: Cooling System Troubleshooting

You can figure it out from Rock auto usually. Or you have to look in the GM parts book, someone made a CD for it, a long time ago, and you could use it on your PC
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Old Today, 05:50 PM
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Re: RESOLVED: Cooling System Troubleshooting

Originally Posted by Flat-twin View Post
I think this is the fan switch
That is the Fan A/C pressure switch. For a TPI and v6 car, if the a/c works, it causes the ECM to trigger the fan(s, year depending) when you turn on the a/c. On a TBI engine, it is a redundant ground to the fan relay (it isn't needed). The a/c high pressure cutoff switch is mounted on the back of the a/c compressor.

Last edited by deadbird; Today at 05:58 PM.
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Old Today, 06:34 PM
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Re: RESOLVED: Cooling System Troubleshooting

Originally Posted by scooter View Post
You can figure it out from Rock auto usually. Or you have to look in the GM parts book, someone made a CD for it, a long time ago, and you could use it on your PC
Thanks I had the same answer from a French Facebook group, I didn't know that site, it's great !

Originally Posted by deadbird View Post
That is the Fan A/C pressure switch. For a TPI and v6 car, if the a/c works, it causes the ECM to trigger the fan(s, year depending) when you turn on the a/c. On a TBI engine, it is a redundant ground to the fan relay (it isn't needed). The a/c high pressure cutoff switch is mounted on the back of the a/c compressor.
Someone told me that it's the a/c pressure switch earlier but thanks anyway (I always appreciate to have an answer and see that I'm not ignored ).
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