Add where you normally would, except, wait until it cools down some. Use caution when you remove the cap and turn your face the other way so that the hot steam does not get all over your face. If possible, use a gloved hand or rags because it will be extremely hot. Prepare to pour your correct mixture of antifreeze and water (seek owners manual) and run the engine while adding. If you don't run the engine, you could crack the engine block.
Your engine is too hot.
Engine coolant.
The water and coolant is put in the coolant reservoir for the location of this refer to the owners manual. It is best to do this when the engine is cold otherwise you run the risk of getting boiling water all over you. the mixture of coolant to water should be about 50/50.
To raise the boiling point of the coolant.
It is not recommended to put plain water in the engine coolant reservoir as a substitute for coolant. While water can temporarily help lower engine temperatures, it lacks the necessary additives to prevent corrosion, raise the boiling point, and lower the freezing point. If you must use water in an emergency, it’s best to replace it with the proper coolant mixture as soon as possible. Always check your vehicle's manual for specific recommendations.
in the coolant resivor
Pressurizing the cooling system raises the boiling point of the engine coolant. under normal conditions this keeps the coolant from boiling and having to be frequently topped off.
When the engine is cool
Cold boiling in an engine occurs when the temperature of the coolant drops below the boiling point due to low pressure, causing the coolant to vaporize despite being at a lower temperature. This phenomenon can result from inadequate coolant circulation, a malfunctioning thermostat, or air pockets in the cooling system. As vapor bubbles form, they can disrupt coolant flow, leading to overheating and potential engine damage. Proper system maintenance and pressure regulation are crucial to prevent cold boiling.
Coolant recovery tank
In the coolant reservoir in front of the engine.
1) Your engine is overheating and the coolant is boiling. Or 2) Exhaust is leaking into the coolant, probably through a bad head gasket or cracked head.