How to safely connect a 1.8v push-pull output to a 3v MCU input?
You could use a zener diode and resistor.







simulate this circuit &ndash; Schematic created using CircuitLab

Pick a Zener voltage between 1.8V and 2.75V. Pay attention to the tolerances to make sure it won't sink current simply from the 1.8V output of the gauge. Also make sure it has a low enough Zener voltage to keep the gauge's pin at a safe level.

For example, pick a diode with a 2.2V Zener voltage. If you want to keep current less than 10mA, you'd need 110 ohm resistor. This assumes the MCU high output is 3.3V, and it can safely drive 10mA of course.

\$\ {3.3V-2.2V\over 10mA}= 110\Omega  \$

EDIT: This assumes the gauge has some reasonable source impedance. You may want to add another resistor of the same value between the diode and the gauge A schematic/datasheet would be helpful. However, at that point, you're at the same component count as a simple, MOSFET level shifter.