I'm working on a boat modernization project and I'd like to replace an analog temperature gauge with an Arduino-based digital solution. The sensor in question is a single-pole thermistor with a common ground to a engine block. The thermistor's resistance range is 15 ... 1000 Ohms.
The existing analog gauge has wires for the thermistor pole and the common ground. I can measure the varying resistance between these wires with my multimeter.
My Arduino Mega 2560 has its own stable 5V power supply that is not connected to the engine block common ground. My question is, is it possible to use an Arduino to read the thermistor in a realiable and safe way? If so, how about multiple thermistors that do not share the same common ground?