My son has a 1988 Fiero GT with a stock 1995 Camaro 3.4L OHV upgrade. It has a 180 degree Tstat and had the oem 235F fan switch. The engine on highway runs 190-200degrees, according to stock temp gauge. But lately noticed that as we got into traffic, the temperature starts creeping up. Past 235, no fan on. Reaching into red area on temp gauge, no fan on. Used to come on. No coolant lines dented or dinged. Coolant full. Radiator, I believe is original, so it is on the list for replacement.

So, with engine off, but keyed on, I did an A/C turn-on check, and electric fan comes on. Pulled fan switch connector, grounded it, fan comes on. Ok, I figure fan switch bad. Ordered Rodney Dickman's 210/200 fan switch with idea I'd be buying some traffic cooling insurance by doing so. Took old 235 fan switch out; the threads had quite a bit of a whitish sealant on them. Cleaned out the manifold threads out as best as could and put in the 210 fan switch with dielectric grease on both connector and switch. But no change, same problem - electric fan does not come on by itself when temperature goes above 210 or 235 or red zone. So, put A/C on while driving, electric fan comes on, and lo-and-behold the temperature starts coming back down to 215-220 range in traffic.

I'm at a loss. So, I'm left with the following possibilities:
1.) Is the fan switch connector making weak connection to the fan switch after 32 years, but good enough when I jam a wire into it to ground it? Therefore, replace connector?
2.) I've heard of parts being bad right out of the box. Could I have a new but bad fan switch? Is there a way to check fan switch itself?
3.) Could there be just enough of the old sealant in the manifold's fan switch threads to be preventing the grounding? Seems unlikely, but any suggestions on better way to clean threads without ruining manifold threads?

Anything else anyone can suggest that I'm missing here before I go and buy connector and another fan switch? Or do you think it's got to be one or the other?
Any ideas are appreciated. Thank you.
Brian

The temperature gauge and/or sender are notorious for reading incorrectly. A scanner (or WinALDL) will tell you the actual coolant temperature as seen by the ECM.

I have the ScanConverter software that reports coolant temp. So, tomorrow I'll give that a try and see what it reports.

Threads should be clean. No tape or grease. That stuff may make a bad ground.

[This message has been edited by Gall757 (edited 05-30-2020).]

Initially, I had put a small amount of Teflon tape at top of threads, per Rodney Dickman's install instructions, figuring I didn't want any leaks. But when fan still did not work, and checked this forum and several others on the topic, most guys said don't use any sealant or tape, unless have to because of a leak. So, took switch out, got the small amount of tape out, and retested with no sealant and no tape. I did not appear to have any leaks, but was once again disappointed that fan did not come on.

quote Originally posted by fast99999: I have the ScanConverter software that reports coolant temp. So, tomorrow I'll give that a try and see what it reports.

To get an idea if the sensors for Coolant and Manifold Air temperature are both okay, tomorrow morning when the car has sat all night, turn the key to ON but don't start the engine. The temperatures reported by both of those sensors should be very close to the outside ambient air temperature.

I'll do that. Good check idea. Thanks.

quote Originally posted by fast99999: ...but was once again disappointed that fan did not come on.

You're probably going to find that the fan's not coming on because the coolant hasn't reached a high enough temperature. It's only May. You're in New Jersey, not Arizona.

That's true Patrick, about 85 today. But I am running an older radiator too, so I figure I'm not running the most efficiently either. Thought about using an infared thermometer too pointed at the fan switch, but not sure the thermometer would get any closer to a real value or not considering tolerances on infared thermometer.

Patrick, I think you are 100% correct. Another case of temperature gauge outta-whack.

I put the ScanConverter on and monitored the Coolant and MAT from start up to long idle, and found the following non-linear data for gauge:

C=Software Coolant Temp, M=MAT, G=Gauge Temp

C=68, M=78.8, G=Below 100 (Before start up - Close to ambient temp of 70 at this moment outside this morning)
C=144.4, M=77, G=140
C=167.9, M=78.8, G=170
C=177, M=80.6, G=180
C=200, M=78.8, G=220
C=216.5, M=82.4, G=Beginning of Red Zone
C=220, M=91.4, G=First 1/3 of Red Zone FAN CAME ON!! (Fan switch is original 235)
C=215, M=95, G=Beginning of Red Zone FAN WENT OFF. (Oem fan switch seems to be working as designed.)

So, dash gauge has non-linear track and clearly not accurate at the higher end of the scale. Gonna take for a ride later to see performance & verify same for on road. But what a relief! Even with 32 year old radiator, still seems to be doing just fine. I haven't used the software for so long, forgot I had it until you mentioned it.
Thanks again Patrick for the suggestion.

quote Originally posted by fast99999: Thanks again Patrick for the suggestion.

You're welcome.

Since you've ordered it, you may as well use Rodney Dickman's 210/200 fan switch when you receive it. A lot of us run that fan switch, just to have the fan come on a little earlier than with the factory 235°F switch.

quote Originally posted by Patrick: Since you've ordered it, you may as well use Rodney Dickman's 210/200 fan switch when you receive it. A lot of us run that fan switch, just to have the fan come on a little earlier than with the factory 235°F switch.

Agreed. Even when "everything is working as it should" it's unnerving to see the temp gauge swing up toward the red before the fan kicks on.


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[This message has been edited by fierosound (edited 06-01-2020).]