With all the electronics the insane engineers are forcing on us, this may no longer apply to your car, but in the past, the dash gauge and the Engine Computer used two different temperature sensors. Sensors for the dash gauge are notoriously inaccurate, but all that's important with those is you notice when there's a sudden change from what you're used to seeing. Sensors for the Engine Computer are much more accurate, and since there will never be two sensors exactly alike, the computer will learn its characteristics by comparing it to other sensor readings and operating conditions.
The only way to know for sure if the engine is reaching proper temperature is to connect a scanner to view live data. That will show you the signal voltage and the corresponding temperature that the computer has calculated. Normal temperature will be around 195 to 220 degrees. If the thermostat is opening too soon, you'll see somewhere around 170 degrees or less.
Wednesday, July 9th, 2014 AT 10:46 PM