Temp Gauge issues 2018 Equinox

[adevl24]

Temp gauge takes 15 minutes to get to "normal." It doesn't fluctuate, just slow to respond. Dealership has replaced the battery sensor and now the thermostat. Little backstory, car also shakes/vibrates when idle, which is why they replaced the thermostat. What can be causing the temp gauge issue? Or is it not an issue, and it's just a norm for my car?

 

[Big Papi]

Without going into a short, book length explanation, the gauge is lying to you by design. An old school add-on gauge that reads directly from a water temp sensor will give you a true and accurate reading. The dashboard integrated PCM controlled one is designed to fib.

 

[Severum17]

Without going into a short, book length explanation, the gauge is lying to you by design. An old school add-on gauge that reads directly from a water temp sensor will give you a true and accurate reading. The dashboard integrated PCM controlled one is designed to fib.

Go to the short book length version. Why would it do this?