Operating temp (Page 1/3)
Rhodesia1977 AUG 02, 10:10 PM
I have a stock 1986 GT with 95k. I drive in an average air temp of 75 degrees. My fan comes on normally and all coolant tubes are good with no leaks. My normal operating temp is about 180 degrees via dash gauge. A couple of times while driving I have noticed that the high temp/ coolant dummy light will come on but very very dim. I can kind of see it when it's dark. I have checked coolant temps with a mechanical thermometer and the coolant is at about 190-195. No other signs of over heating occur. No codes from the computer when tested. A new coolant sensor was installed last year. Any suggestions? Thank you!

[This message has been edited by Rhodesia1977 (edited 08-03-2022).]

J Gunsett AUG 03, 10:53 AM
I had this happen to me also. This happened a coupe time but only in raining conditions. I am not sure if moisture was getting into the sensor or the wiring to let voltage go to ground.

Jack
olejoedad AUG 03, 12:28 PM
The fan is controlled by the fan switch, not the temp sensor.
The fan switch is located on the passenger side of the engine, on top, near the coolant fill.
greenturnedblue AUG 03, 01:02 PM
Do you have a 180 or 195* thermostat?
fierofool AUG 03, 03:20 PM
Your lower temperature reading could also be due to a slipped gauge needle. Does it sit on the round portion at the bottom of the thermometer symbol when the ignition is off and at ambient temperature? It should.
Rhodesia1977 AUG 03, 04:58 PM

quote
Originally posted by fierofool:

Your lower temperature reading could also be due to a slipped gauge needle. Does it sit on the round portion at the bottom of the thermometer symbol when the ignition is off and at ambient temperature? It should.



Yes it does. I checked the temperature at the thermostat housing with a laser thermometer and it said 198 and my needle said 195 so I believe the needle is close. I just wanted to know why my over temp light comes on very dimly sometimes. I check it at the coolant sensor and grounded each wire and my needle moves and my over temp light comes on fully. I don't know what kind of t stat I have as I am afraid to open it and then try to mess with burping the system and all that. I guess I'll just try to keep an eye on things. If my engine was overheating wouldn't there be the typical signs?
Patrick AUG 03, 08:29 PM

quote
Originally posted by Rhodesia1977:

I just wanted to know why my over temp light comes on very dimly sometimes.



I would think that light should either be ON or OFF... not illuminating dimly. I would suspect a possible bad ground somewhere.


quote
Originally posted by Rhodesia1977:

I don't know what kind of t stat I have as I am afraid to open it and then try to mess with burping the system and all that.



Keep in mind that when a Fiero is sitting level, the thermostat housing is the highest point of the cooling system. No air will be introduced into the system by removing the cap and/or thermostat.
greenturnedblue AUG 03, 08:58 PM
I dont think the dummy light is meant to come on until 230* and by that temperature damage has already been done. But, if your gauge says 195* and the digital thermometer says 198*, safe to say the gauge is correct and the car is operating in the correct range (stock thermostat temp is 195*).



As you can see, there isnt much else going through that C2 connector. It is puzzling how it is 'half on'. I would check if that C2 connector is loose, or wires are frayed and causing current to jump over, completing the circuit and illuminating the bulb. Maybe power from the door ajar light is crossing over? I would test resistance between pin 11 on the C2 connector, and every other pin. they should all be open and if there does appear to be resistance between pin 11 and another, it means current is crossing over from something else

As Patrick said, test resistance between pin 11 on the C2 connector (overheat light) and the main engine ground. then, you will see if it is grounding properly
Kevin87FieroGT AUG 03, 09:36 PM
If the engine is cool, you should be able to open the coolant fill port on the engine and easily swap out your thermostat. Doing this with the cool engine will greatly minimize or eliminate any coolant spillage. You might need pliers to help pull the stat out.

When putting the new stat in just go slow and you won’t lose any coolant. Make sure it’s fully seated. No need to “burp” the system when done.

Get yourself a new Stant Super Stat 195*.

Cheers
Fiero_Adam AUG 03, 11:01 PM
Maybe there's no light bulb socket in that spot and you're getting some light pass through occasionally?