1985 GT 2.8l - The radiator fan will NOT come on when the engine reaches temp.
The fan DOES work with the A/C switch on and also when 'hotwired', so the fan itself and relay are good.
I've replaced the coolant fan switch (the sensor next to the t-stat housing with the one-wire connector), but it did not help.
The temp gauge works properly as well.

Thoughts on what I can check next?

Thanks,
Dan

Although I don't know too much about this, my understanding is that the fan will not turn on until the temp gets to 235. Are you letting it get to that temperature?

[This message has been edited by IMSA GT (edited 11-12-2023).]

quote Originally posted by IMSA GT: Although I don't know too much about this, my understanding is that the fan will not turn on until the temp gets to 235. Are you letting it get to that temperature?

235 seems high, but I don't know the temp either. I let the engine get to 225, which was high enough for coolant to spew out of the coolant overflow tank (has a new cap).

EDIT**: After some more research, the switch kicks on the fan at 230. I never let it get that high, mainly due to the coolant spewing from the tank. Maybe it was overfilled, I dunno.

I'm going to ground the connector at the switch to make sure the wiring is good.

[This message has been edited by dhardison (edited 11-12-2023).]

Coolant coming out of the overflow?
Seems like you have a bad radiator cap.
Check the hoses when the engine is running and warm. Are the hoses fairly rigid? If not, you haven't the right pressure in the cooling system.

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"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM

quote Originally posted by Frenchrafe: Coolant coming out of the overflow? Seems like you have a bad radiator cap. Check the hoses when the engine is running and warm. Are the hoses fairly rigid? If not, you haven't the right pressure in the cooling system.

nice call as said is "boil over" & dash gauge reads < 250°F... If true, yes something is wrong but can be more then rad cap problem.

Coolant mix is first to test w/ any "float" tester because below 50/50 mix will easily "boil over."
Example: Any that put premixed coolant after flushing will have weak coolant because system has a lot of trapped water.
watch https://www.youtube.com/watch?v=GW-iI9Vgx58 Note that old coolant may be Ok for boil/freeze but lost anti rust & other additives that any float types can't tell.

That even w/ 15-16psi non-vent rad cap...

See https://web.archive.org/web...erocave/coolfill.htm & rest of section

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

I believe the schematic will help and check the coolant temperature switch wiring



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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 11-13-2023).]

Thanks to all for the replies/info. Here are some updates from my end.

- I grounded the radiator fan switch at the connector and the fan comes on, so the wiring is good.
- I tested the coolant and the freezing point shows well above a 50/50 coolant/water mixture
- I fired up the engine and let it come up to temp long enough for the high-temp idiot light to illuminate on the dash, but the fan never came on. It also did not puke anything out of the front tank, so I may have just had it overfilled. The coolant hoses were tight, so it's building/holding pressure.

At this point the only way to get the fan to kick on is to engage the A/C or hotwire it.

So, all the following is new (all from RockAuto):
Radiator fan switch
Radiator cap (engine)
Thermostat

I'll check the schematic and see what I can determine, but for whatever reason the radiator fan switch doesn't appear to be doing its job. Faulty (new) sensor possibly......

[This message has been edited by dhardison (edited 11-13-2023).]

quote Originally posted by dhardison: I'll check the schematic and see what I can determine, but for whatever reason the coolant sensor doesn't appear to be doing its job. Faulty (new) sensor possibly...

I assume you're referring to the fan switch.

A lot of us use Rodney's 210° on and 200° off fan switch.

quote Originally posted by Patrick: I assume you're referring to the fan switch. A lot of us use Rodney's 210° on and 200° off fan switch.

Yes, the radiator fan switch. I bought the following from RockAuto (https://www.rockauto.com/en/moreinfo.php?pk=929686&cc=1249040&pt=4312&jsn=5).

Thanks for the info on the Rodney Dickman switch. Sounds like it's worth a try.

quote Originally posted by dhardison: So, all the following is new (all from RockAuto): Radiator fan switch Radiator cap (engine) Thermostat

You must check the Rad Cap is a Non-vented Cap. See Rad Cap in Cave.
Do Not trust RA or anyone else, including "Stant" parts since since Stant is Gone.