See if this makes sense. I've had my '80 for 32 years. I always relied on the factory dash "idiot light" until about 3 months ago when I finally decided to install 3-way gauges. While I was at it, I figured, "Why not replace the original temp sensor that goes to my dash?" That way I'd really have two temp sensors (light and gauge). My temp gauge needle is always between 195 -200. But after about a month of having the new temp (idiot light) sensor replaced, it started glowing red. I figured it was a bad sensor, so I changed it this morning and the new one is glowing too. Ggrrr! It starts glowing at about 150 degrees and then stays full red when completely warm. The gauge needle never moves from 195-200. Does it make sense that the dash light sensor (sent from the lower side of the block) would indicate red, when my gauge needle (from the top of the manifold) stays consistent at 195-200? Ideas - other than just disconnecting the temp sensor wire going to my dash? ha.

 

Update: OEM sensor (idiot light) still glows red after warm-up even though my after-market gauge (needle) stays constant at 195 degrees. I did notice this morning the old trick of turning-up the heater seemed to lower the temp glow light intensity, but again my after-market gauge never moved past 195. Is there any explanation as to why my OEM temp sensor on the side of my block would seem to indicate high temps when my after-market needle gauge rides smooth at 195 on top of my intake manifold?

 

In 1980 they used a 180° temp thermostat. The 195° thermostat may be triggering the light. Try replacing the 195° thermostat with a 180°.

 

I completely agree with Mike (03SSLE)

195 is waaay to hot for that model year.

I would also go by the factory temp sensor in the intake manifold...

Convert it to an aftermarket one just to be sure. the temps are running correctly....

Besides...
That's why they call them idiot lights...

 

Thanks guys. I'll make it a point to change the thermostat back to 180 at my next opportunity. Wish I would've known that years ago. Like you said, at least I have the aftermarket Sunpro gauge in my intake which stays steady at 195. Thanks again.

 

UPDATE: After several cooling system drains and process of elimination, my problem was either the $10 Advanced Auto electric temp sensor or the wiring that goes to the dash light itself. I've gone through 2 sensors and messed with the wiring and connection over & over with no improvement. So yesterday I did two things: 1 - I replaced my T-stat from 195 to 180. It didn't resolve the original dash idiot light problem, but my car is running cooler - close to 20 degrees cooler. 2 - I bought another (single) temp gauge from AutoZone. I installed that one where the factory elect temp sensor was on the pass side of the block, and it stayed right at about 180. My other gauge to the manifold runs about 5-8 degrees cooler which I would expect since the temp sensor on the block/head runs a bit hotter right next to the cylinders. I'm not motorhead, just a guy who has tried to keep his '80 going since I got her in '83. But this one bugged me. No more electric dash sensor. I'll just leave the 2nd temp gauge in and use them both. It gets hotter than hell here in South Texas, and I like having accurate temps on my tiny little V6 229 w/ over 260K on it. Have a good day MCF.