I am running a 2020 L84 crate motor in my 71 Lemans. It has the DOD delete LS6 lifter kit and running a LT1 spec cam. The Lemans has the factory gauges, which functioned fine before the swap. The 2014 PCM I am using uses a 2018 temp sensor (threading difference) in the stock location, the steam gauge in an adaptor where the block heater goes. I get a 30-40 degree F disagree between the two; the PCM sender reading at one time 240 F (!). Concerned of course, I pulled over and checked the engine temp with a laser temp gauge - calmly running about 180 - 200°. The ECM was being monitored by Torque Lite app on an Android.

I also noted a slight lesser disagree in my 2016 but reversed: gauge says 210° while Andy say 180°.

What gives?

 

I'd say your 2014 PCM / operating system is expecting the temperature resistance profile from a 2014 temperature sensor - which is different than the 2018 sensor you are running. Use an adapter from the Autometer gauges folks to eliminate the threading difference and then put a 2014 sensor into the hole.

As an aside, I also see significant front-to-rear temperature differences in the LS engine poked into my 70 El Camino. But . . . it REALLY is about 20 degrees hotter at the passenger side rear corner than the drivers side front corner as indicated by an infrared thermometer. Thusly, some of what you are seeing could actually be true.

Rick

 

I ran this same drill again today with the L83 powered GMC; still big gauge/scanner disagree but the gauges stayed at 210.

I am just going to run both vehicles as the gauges seem to be accurate enough to warn of thermal carnage.

Thanks