Don’t open the radiator cap until it is cool Note that an overheated engine may have a coolant that is as hot as 260 Fahrenheit. Inside the system is sealed. Unfortunately, once it is exposed to air, it will boil and can cause severe burns to you.

The most common is a metal push and turn cap. This cap is typically round in shape with ears sticking out from each side. To remove this type of cap, push down while simultaneously turning the cap counter clockwise. These caps can be found at the top of the radiator itself or close by depending on the type of engine.

On all vehicles that have a reservoir you add it to the reservoir, unless it is totally empty, then you can add it to the radiator directly. Once the radiator is full you will want to finish topping it off through the reservoir. If you just need to add because it is loww, then always use the reservoir.

You should never open the radiator cap while the engine and coolant are hot. Opening the radiator cap while the coolant is that hot can cause the boiling coolant to surge out of the radiator and cause third degree burns on any skin it gets on – yours. So, wait for the coolant to cool before opening the radiator cap.

Typically though it should be left to cool for 1-2 hours before it’s cooled sufficiently to open the rad cap safely. If you’re actually trying to check the coolant level then you probably need to wait more like 3-5 hours (as if the coolant is still warm it will show a falsely high reading due to expansion).

It’s dangerous to remove the pressure cap from the radiator or coolant recovery system reservoir while the engine is still warm. Never remove the cap from a radiator or coolant recovery system reservoir when the engine is hot. Adding cold water to a hot engine can crack the engine block.

Never Open a Hot Radiator Cap Wait until your car’s engine has cooled down completely before opening the cap, or simply check the coolant level before turning on your engine. If you can see coolant in the radiator, and it’s near the top (approaching the cap spout), then you don’t need to add any additional antifreeze.

Can I add coolant/antifreeze to a hot car? In instances where an engine has overheated, causing a breakdown, there may be a need to add fresh coolant/antifreeze to the cooling system. However, you should never add coolant/antifreeze when the engine is hot, and instead wait for it to cool.