For a game, Car Mechanic Simulator is pretty realistic. Most of the components, from every nut and bolt, including how they all go together, are reflective of how cars work in the real world. Just like IRL wrenching, you need to put things together properly, or it won't work. It's not just the mechanicals either, as the electrical and electronics, including aspects around restoring, tuning, and repairing cars are uncanny between the game and in real life. There are even fluid mechanics designed to make sure you don't spill your motor oil during a service! Granted, CMS isn't 100% realistic, but it's perhaps the most realistic car-wrenching sim yet.