Engine running hot

Couple things first. If the engine runs hot, what does that mean? Can you get a picture of the gauge where it shows where it is running hot? Then do you know what thermostat he installed? They have different temperature thermostats so he may have put one in that opens at a higher temperature.

Let's start with this and go from there. Thanks

https://www.2carpros.com/articles/symptoms-of-an-overheating-engine