The Car Doctor in the video “How I Can Feel Pressure In My Coolant System”, discusses why you should never change the coolant in the radiator when the engine is hot. The coolant in the radiator gets extremely hot when you run the car or vehicles. The coolant has water in it, and it heats up to a high temperature when you are driving. If you were to open the radiator cap or remove it when the engine and radiator are hot, boiling water would spray out. You can be seriously injured if it hits your hands or face.
This is how high-pressure coolant systems work.
If you plan to change the radiator coolant in your car, truck, or vehicle, make sure it is cold and you have not been driving around. High pressure coolant systems can heat up to hot temperatures, making it dangerous to change the coolant after driving. When the radiator and engine are cold, you can remove the radiator cap and put in the coolant. If you are not mechanically inclined, it is better to have your local garage add fluid or flush out your radiator. They have the tools to do the job correctly on high pressure coolant systems.